Suspension Assembly on an Indy Car

This primer will detail the theory behind the major suspension assembly on the DW12 and IR-18 Indy Car. It will also consider the use of the individual suspension units in controlling mechanical grip and balance. The primary suspension units detailed are the main springs, their associated dampers and tuning valves, the 3rd spring and the control arms that link the main springs to the 3rd spring. Also, anti-roll bars will be included in the discussion, since many of the concepts apply to anti-roll bars as well.

Before the roles of anti-roll bars and springs (and dampers) are examined, some important concepts need to be introduced. They are  inertia, weight transfer, chassis roll, forces in a turn and banking.

Weight transfer basics-

The concept of  loading/unloading of tire contact patches needs to be understood before any discussion of suspension units takes place. "Load" refers to an excess of force on a corner of the car. "Unload" refers to a deficiency of force on a corner of the car. These forces occur from  acceleration, deceleration, aerodynamics and turns - both flat as well as banked.

The property (inertia, explained below) causing loading and unloading, has both a vertical and horizontal component. Consider the following diagram for a loading force in a turn:

These 2 components create forces opposing each other. The horizontal component creates an "inertial force", pushing the car to the outside. The vertical component creates grip - a frictional force that opposes the outward "inertial force" and pushes inward. This is the balancing act tires play between the 2 forces. If the frictional force exceeds the "inertial force", grip is maintained. If the "inertial force" is greater than the frictional force, the tire's limit of adhesion is reached and grip is lost. This is shown in the following diagram:

Acceleration, deceleration and aerodynamic forces occur longitudinally (lengthwise) in a car. So, only springs and dampers can be used to control them. Forces in a turn occur laterally (crosswise) in a car - and are referred to as "roll" force. The vertical components are controlled by springs and dampers. The horizontal components are controlled by anti-roll bars. The two combined - both anti-roll bars and springs - create the total roll stiffness of the car in a turn.

Loading and unloading of a tire contact patch may not necessarily be bad. If the load amount on a tire is well below the limit of adhesion, then adding load might allow for more grip. Conversely, if the load amount on a tire is excessive (overloading), then removing load (creating unload) might decrease its tire wear.

While a car is braking, accelerating or turning, inertia from the car’s mass creates more or less load on a car’s corner and associated tire. Inertia is the tendency of an object to resist a change in motion. An object at rest resists movement. An object in motion remains in motion. Understand that inertia is NOT a force. It is sometimes incorrectly referred to as “centrifugal force”. When an object is in a centrifuge, it is the inertia of the object that causes it to get plastered to the outside of the centrifuge, not any force!! Inertia can create forces (loading and unloading forces), but it is a concept, not a force.

Any change in an object’s motion will exhibit inertia. For example, if a car is at constant speed or at rest, inertia is not invoked. However, in a turn, the car is changing direction, so its motion is changing. Inertia is invoked – and the car will resist that change in motion in the turn. With no force to oppose the inertia of the car (like friction from the track surface), the car will continue on a straight line at the instant it enters the turn. So, there must be some external force (to negate the effects of inertia) that will cause the car to turn into the corner – like friction from the track surface and/or banking in a turn.

The amount of inertia an object possesses is proportional to its mass and speed. So, the more mass an object possesses, the larger its inertia. Also, the faster it moves, the larger its inertia. On a fast sequence of right/left (or left/right) hand turns on a road/street course, inertial effects can be huge - especially on the front of the car.

Each time that inertia is invoked by a car’s change in motion, the loading and unloading process of tire contact patches from one tire to another tire will occur – referred to as “weight transfer”. So, inertia causes “weight transfer”. The actual weight of the car doesn't change or move around to different corners and tires, but if you could place a scale under each wheel while driving, you would see what appears to be shifts in weight at each tire. In reality, these changes are due to inertia, either pushing a tire into the track (loading) or lifting the tire from the track (unloading). All forces acting on the car are measured in units of pounds, so "weight transfer" is a common name for it - even if there is no actual weight being transferred to a car's corner. Even loading and unloading amounts from inertia are measure in units of pounds – and are referred to as “forces”. But inertia, by itself, is not a force – just a consequence of an object changing its motion. So, the loading/unloading process is not really caused by any force, but is sometimes called “inertial force” – a misnomer. “Inertial force” will always be put in quotes, just like “weight transfer” – so the reader is aware of the misnomers. It is a lot like using the phrase “centrifugal force” to explain the consequences of inertia. “Inertial influence” might be a better term – when you see “inertial force” think “inertial influence”…when you see "weight transfer" think "load transfer".

If a corner of the car is loaded by “inertial influence”, that means the corner “weighs” more than at rest or at constant speed. If a corner of the car is unloaded by “inertial influence”, that means the corner “weighs” less than at rest or at constant speed. Understand that in this case, the corner still “weighs” something, just less than what it would at rest.

Also, in a turn, the loading/unloading amounts have a vertical and horizontal component – so, inertia causes a downward/upward as well as outward/inward influence on the car’s corners.

Effect of load on grip level -

 In general, as load is added to a tire, the coefficient of friction between the tire and the track surface will decrease. This is known as tire load sensitivity and is due to the elastic properties of rubber. Consider the following table:

Notice that the coefficient of friction decreases as vertical load on a tire increases. Using this fact has huge ramifications on loading and grip level. With some physics principles, the coefficient of friction can be mathematically combined with load amounts and frictional force to create the single most important, fundamental relationship between vertical load amounts and grip levels:

Grip levels increase with increasing vertical load, but by a diminishing amount.

Putting this relationship in another way:

A tire’s efficiency in creating grip decreases with increasing load.

What does this mean? It means that adding load to a tire will increase its grip level, but not linearly. The more load that is added, the less the grip level increases. Adding twice as much load yields LESS THAN twice as much grip level.

This important relationship between tire loading and grip level can be seen in the following diagram:

 (The diagram uses Newtons as its unit of force/load measurement)

Notice that the green line relating vertical load to grip level is not straight - but curved to the right (its slope decreases). The relationship between tire loading and grip level is non-linear. This is a vitally important concept to understand.

The result of the relationship between grip levels and vertical loading has another related consequence:

A tire will lose grip as it is unloaded. A tire will gain grip as it is loaded. However, the amount of unloading/grip loss always exceeds the amount of loading/grip gain.

This fact will become important when controlling the rate of load transfer between opposing suspensions is discussed below.

Load transfer between opposing suspensions -

So far, the discussion on tire loading/unloading and the associated grip levels produced have only involved one tire. However, "weight transfer" (load transfer) occurs between 2 opposing suspensions in a car  (either front-to-rear, rear-to-front, side-to-side or diagonally). So, the loading/unloading concepts seen above will now be applied to 2 (or more) tires. A new, important result will be seen and lead to the fundamental property of "weight transfer" (load transfer) in a moving car.

Load transfer between opposing suspensions requires that one of the tires will be unloaded, while the other tire will be loaded. That is how load transfer works. Both suspensions need to be treated as a single unit to see how load transfer affects the entire system.

Recall the previous diagram relating tire loading and grip level:

Confused how it can be applied to load transfer?? Let's look at an example:

Let's say an Indy car, travelling in a straight line, has a 3600 N (800 lb) load on each of the rear tires. Using the diagram above, that vertical load equates to 4500 N (1000 lb) grip level. So, for the 2 rear tires, the total grip level for the rear tires is 1000+1000=2000 lbs. In other words, it would take 2000 lbs of lateral force to break the grip on the rear axle.

Now, let's put the Indy car into a turn. If there is about 50% lateral load transfer on the rear tires, then the outside tire would have an increase of 400 lbs or a total of 1200 lbs of load. The inside tire would have a decrease of 400 lbs or a total of 400 lbs of load. Using the diagram above, 1200 lbs of vertical load equates to 6500 N (1450 lb) grip level for the outside tire. 400 lbs of vertical load equates to 2200 N (488 lb) grip level for the inside tire. So, for the 2 rear tires, the total grip level for the rear tires is 1450+488=1938 lbs. In other words, it would now take only 1938 lbs of lateral force to break the grip on the rear axle. That is 62 lbs LESS grip level capability. Furthermore, the unloaded tire lost 512 lbs of grip potential, while the loaded tire gained only 450 lbs of grip potential. This is shown in the example below:

Now, let's do a similar example with the entire car. The first set of data is for an Indy car at high speed on a straightaway. The second set of data below it is for an Indy car at high speed in a turn. Total load is a combination of static “weight” of the car and downforce. Although the numbers are approximates, they are reasonable:

Notice that total vertical load has stayed the same in each case - total load is never reduced due to load transfer. However, look at the total lateral load (total grip level). The car has lost 81 lbs of total grip level capability. So, load transfer has caused a loss of total grip level in the car. Also, there is more grip level in the front of the car than in the rear of the car. Only running the car on a track will determine if the car is out of balance, but balance has definitely shifted to the front of the car.

 These examples provide data that support the following Rule of Weight Transfer:

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Weight Transfer (load transfer) creates a net loss of total grip on opposing tires.

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Of course, there are 2 sets of opposing suspensions on a car. Although load transfer is considered to be between 2 opposing suspensions, it involves both sets of opposing suspensions (front and rear or even inside and outside). So, load transfer (as a whole) occurs throughout the entire car and through BOTH sets of opposing suspensions.

If both sets of opposing tires (all 4 tires) are combined together and treated as one complete grip unit for the entire car, then weight transfer can be generalized into the following  General Rule of Weight Transfer:

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Weight Transfer (load transfer) creates a net loss of grip throughout the entire car.

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So, load transfer will affect the grip level of ALL 4 TIRES. The loss of grip is felt overall - throughout the entire car.

Also, there will most likely be a shift in the balance of the car. There are many possibilities for creating imbalances throughout a turn, especially on a road course. On a road course, extreme changes in speed and direction will create all sorts of imbalance possibilities. The front of the car may have more lateral load capability (grip level) than the rear of the car for a short, transient time - and vice versa.

But...what if we could somehow delay the transfer of load that causes all of these grip issues until the car is far enough into a turn that grip levels are not so compromised?

There is no way to control the AMOUNT of load transfer to a particular corner (and tire) of a car. Physics dictates the rules! But, the RATE at which the load transfer takes place can be controlled.

Delaying “weight transfer” (load transfer) -

From the previous discussions above, it is apparent that load transfer reduces overall grip level. Delaying load transfer for as long as possible will help maintain grip level for as long as possible. If the delay is long enough, the bulk of the time spent in a turn with too little grip can be minimized.

Although the topic of load transfer deals with its effect on one set of opposing suspensions, recall that BOTH sets of opposing suspensions are susceptible to load transfer. So, while the following discussion on delaying load transfer (to delay grip loss) applies to one set of opposing suspensions, the criteria will be applied throughout the entire car - and to BOTH sets of opposing suspensions. The following diagram illustrates:

To delay the load transfer as much as possible, slowing the unloading/loading process needs to be accomplished in the opposing suspensions. The unloaded suspension unit needs to discard its load as slowly as possible. The loaded suspension unit needs to accept its load as slowly as possible. Any increase in the unloading/loading process will speed up the load transfer - and reduce available grip levels in the associated tires.

How can load transfer to opposing suspensions be delayed? Consider the following 2 diagrams. The first diagram illustrates load transfer with a solid bar being used to support a weight:

In this case, the weight is supported by a solid bar. If a scale was placed at the base of the pedestal, it would measure an initial weight of 15 lbs - immediately. After 1 second, it would also measure the weight at 15 lbs. So, “weight transfer” in this case is immediate, with no delay. The load is immediately transferred to the scale.

The second diagram illustrates load transfer with a spring being used to support a weight:

In this case, the weight is supported by a spring of some arbitrary strength. If a scale was placed at the base of the pedestal, it would measure an initial weight of 0 lbs. After 1 second, it would measure the weight at 13 lbs. After 1.5 seconds, it would measure the weight at 15 lbs. So, “weight transfer” in this case is delayed. The load is NOT immediately transferred to the scale.

In both cases, the load is completely transferred to the scale. With a spring, however, the load is delayed. It can be shown that the STRENGTH of the spring will determine how long the load transfer will be delayed. A stiffer spring will delay the load transfer less than a softer spring. A softer spring will delay the load transfer more than a stiffer spring.

This important characteristic of a spring can be generalized to dampers and anti-roll bars (ARBs). All 3 suspension units have the ability to delay load transfer. The ability to control the RATE of load transfer to a tire by springs, dampers and ARBs has huge implications on maintaining grip in a turn.

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NOTE: - and this is important - there are many reasons for choosing stiffer settings on suspensions over softer settings. Responsiveness, balance, driver preference and so on can be of equal or greater value than limiting the rate of load transfer. The positives of stiffer suspensions may simply outweigh the negative consequences. In reality, delaying load transfer may have to take a “back seat” to other uses for suspensions in the car. But, it is still an intriguing concept to understand.

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Anti-roll bars, springs and dampers all help to control these loading/unloading amounts. Anti-roll bars control the horizontal (lateral) component. Springs and dampers control the vertical (longitudinal) component. It is crucial to understand that they cannot reduce the amount of  loading/unloading. The inertia of an object cannot be changed. Physics won't allow it. Suspension units can, however, control those “inertial influences”. This control can have profound effect on the grip level of the tire contact patches.

Finally, understand that the amount of "weight transfer" is solely a function of the amount of inertia. The greater the inertia, the greater the loading/unloading amount of tire contact patches from one tire to another tire.

Pitch and roll axes -

Consider the following diagram of the rotational axes that "weight transfer" (load transfer) acts through:

There are 3 possibilities for “weight transfer” to act through these axes:

1. Acceleration - At constant speed (or at rest), all four tire contact patches are in a neutral loading/unloading state. As a car accelerates, both front tire contact patches unload by the same amount and both rear tire contact patches load by the same amount. This means that "weight transfer" occurs from front to rear tires. There is now more load on the rear tires and less load on the front tires. After acceleration is finished, all four tire contact patches return to their neutral loading/unloading state. The inertia acts through the pitch axis of the car. It can be seen as the car's rear end "squatting".

2. Deceleration - At constant speed (or at rest), all four tire contact patches are in a neutral loading/unloading state. As a car decelerates, both front tire contact patches load by the same amount and both rear tire contact patches unload by the same amount. This means that "weight transfer" occurs from rear to front tires. There is now more load on the front tires and less load on the rear tires. After deceleration is finished, all four tire contact patches return to their neutral loading/unloading state. The inertia acts through the pitch axis of the car. It can be seen as the car's front end "diving".

3. Cornering - Before entering a turn, the car may be at constant speed, accelerating or decelerating. However, the lateral side-to-side (inside to outside) loading/unloading of all four tire contact patches is in a neutral state. As a car enters a turn, the inside tire contact patches unload and the outside tire contact patches load. This means that "weight transfer" occurs from inside to outside tires. There is now more load on the outside tires and less load on the inside tires.

As a car exits a turn, the opposite happens - the inside tire contact patches load and the outside tire contact patches unload. This means that "weight transfer" occurs from outside to inside tires. The excess load from the outside tires returns to the inside tires. Also, since the front wheels of the car are turning into and out of the turn, the outside front tire contact patch loads/unloads more than the outside rear tire contact patch. After the turn is completed, the side-to-side (inside to outside) loading/unloading of all four tire contact patches returns to their neutral state.

The inertia in a corner acts through both the roll and pitch axis of the car. It can be seen as the car's chassis "rolling".

Chassis roll is a natural byproduct of both vertical and horizontal components of  the loading/unloading amount from inertia in a turn acting through the roll axis - as well as spring strength and anti-roll bar strength. Therefore, chassis roll also has 2 components to it - a vertical component and a horizontal component. The loading/unloading of tire contact patches (or "weight transfer") occurs with or without chassis roll. If the springs and anti-roll bars had infinite strength and resistance, the same amount of "weight transfer" would still happen - just not chassis roll. So, chassis roll is simply the result of less than infinite resistance of the springs and anti-roll bars from keeping the chassis perfectly parallel in a turn - and is a natural consequence of inertia. For a given spring and anti-roll bar strength, the larger the “weight transfer”, the greater the chassis roll.

Chassis roll by itself is not necessarily bad. In fact, chassis roll is a visual clue that unloading/loading of the tire contact patches is being controlled. It results from the suspension being "soft" enough to allow the roll (and temporarily absorbing and delaying some of the loading/unloading amount), rather than the loading/unloading being imparted directly to them. So, chassis roll is visual proof that the suspension is doing its job. Understand that chassis roll does NOT cause "weight transfer" to occur. "Weight transfer" occurs because of the inertia of the car's mass - and happens whether chassis roll occurs or doesn't occur. Chassis roll is the RESULT of "weight transfer", spring strength and anti-roll bar strength - not its cause.

During chassis roll, the car's body is no longer parallel to the track surface - and neither is the suspension's geometry. Even though the suspension allows the wheels to be somewhat independent from the chassis, the extreme “inertial influence” in a turn (and the resulting chassis roll) can reduce the suspension's ability to keep the tire parallel to the track surface. At some point, the chassis roll will take the suspension beyond its limit of "give and take" - disrupting the tire camber and the tire contact patch will no longer be fully in contact with the track surface.

Too much chassis roll, then, can cause the suspension geometry to change - creating issues with tire camber and the tire contact patches surface areas.  Excessive chassis roll simply means that the suspension is too "soft" - too compliant. Over a longer run, excessive chassis roll can increase tire wear and lessen grip. It is the cumulative wear on the tires over several laps that will be noticed if chassis roll is too extreme. So, some chassis roll is desired - as it is proof that suspension strength is at a proper level. Too much chassis roll (from too little suspension support) however, will create grip issues over time.

So far, these potential issues with grip (“inertial influence”, "weight transfer", chassis roll, etc.) are found equally on ovals as well as road/street courses. A turn is a turn! But...

Other forces in a turn -

In addition to “inertial influence” from the car's mass affecting loading/unloading amounts (and grip), the track imparts its own opposing vertical force to oppose the vertical component of the loading/unloading force from inertia. The track is "pushing up" (or to be more precise, resisting the vertical loading/unloading force - including the car’s weight) against the bottoms of the tires. This force is equal and opposite to the vertical loading/unloading force on all 4 tire contact patches.

In addition to the vertical force from the track, friction between the 4 tires and the track surface creates a horizontal “centripetal force” that pushes the car toward the inside center of the turn. This force is derived from the vertical components of the loading/unloading force from all 4 tire contact patches and the coefficient of friction. Without this frictional force, the car’s inertia would keep the car moving in a straight line – and never make the turn! This is the “grip” that keeps the car turning in a turn.

At the entry to a turn, inertia unloads the inside tire contact patches and loads the outside tire contact patches. This creates more load on the outside tire and less load on the inside tire. In effect, the outside corners of the car “weigh more” than the inside corners.

At the exit to a turn, inertia unloads the outside tire contact patches and loads the inside tire contact patches. This process returns the excess load of the outside tires back to the inside tires. The outside corners and the inside corners of the car “weigh” the same as they did before the turn was entered.

Banked turns add a horizontal component to the track's usual opposing vertical component force (described above). This horizontal component adds to the frictional force already present between the 4 tires and the track surface. This additional force creates more horizontal “centripetal force” and pushes the car to the inside center of the turn with more force than a flat turn.

Since a banked turn possesses a horizontal component to its force, it can also reduce the horizontal component of the loading/unloading force on the car’s corners. This will indirectly reduce horizontal (lateral) chassis roll in a banked turn.

Consequently, a banked turn results in less horizontal (lateral) chassis roll than a flat turn. Conversely, a flat turn results in more horizontal (lateral) chassis roll than a banked turn. The amount of lateral chassis roll reduction is directly proportional to the bank angle. A higher bank angle results in a higher lateral chassis roll reduction. Remember that excessive chassis roll can impact the camber of a tire and reduce the tire contact patch size, affecting tire wear and grip.

In addition to adding a horizontal component to its usual opposing vertical force, a banked turn also adds a vertical component to the existing horizontal frictional "centripetal force". This additional vertical force adds to the existing vertical loading/unloading forces from inertia of all 4 corners of the car.

For this reason, a banked turn will result in more vertical loading of all 4 tire contact patches than a flat turn. This means that the outside tire contact patches will load more – and the inside tire contact patches will unload less – than a flat turn.

The increase in vertical loading from a banked turn can cause overloading - especially on the outside suspensions. This excess loading can cause excessive friction between the tire and track surface, resulting in excessive tire wear. The added friction can increase tire temperature and eventually, loss of grip.

To put it in simpler terms:   more bank angle = less horizontal (lateral) inertial influence = less horizontal (lateral) chassis roll = less suspension geometry change = less tire camber misalignment.

The following diagrams show the forces in a flat turn and a banked turn:

From a quick analysis of the above diagrams, it can be seen that a banked turn creates a horizontal component and a vertical component to the forces from friction and from the track. The horizontal components add together to help keep the car turning, rather than going straight ahead. The vertical components add together to increase load to all 4 tire contact patches. And, the resultant forces are larger on a banked turn than on a flat turn.

Also, the physical weight of the car will alter the loading of the suspensions and tires in a banked corner. Since the inside tires are below the center of gravity, and the outer tires are higher than the center of gravity, some of the static load (weight) is transferred from the outside to the inside - and is proportional to the bank angle.

Consider the following diagram of how the car's static weight creates more load on the inside suspension in a banked corner:

Notice that outside suspensions actually lose some load, while the inside suspensions gain some load from the banking. The additional load on the inside suspensions helps lessen some of the loss of loading from inertia in a corner.

Finally, a flat turn will possess much more lateral chassis roll than a banked turn - and will need to be controlled with a "stiffer" suspension (i.e. anti-roll bars). Also, the radius of a turn and its speed will affect overall chassis roll. A tighter flat turn with a higher speed will create more overall chassis roll than a flat turn with less radius and slower speed. For example, a one-mile flat oval has fast, flat, tight-radius turns. Thus, its turns result in a lot of “inertial influence” being present - and create a lot of chassis roll.

And, a banked turn will increase the “centripetal force”, helping the car “stick” to the track. This increased force is why less aerodynamic downforce is needed in a banked turn. The lack of downforce grip is made up by the increased horizontal force from the banking. Of course, the larger the banking angle, the greater the horizontal force - and the less lateral chassis roll.

Controlling all of this "weight transfer" and chassis roll is the key to maintaining grip in the tires’ contact patches.

Now, let's consider the major suspension units in detail:

1. anti-roll bars (ARBs) - used to reduce the horizontal (lateral) component of chassis roll during cornering (discussed in detail below). They add to the vertical roll resistance of the car's main springs without having to resort to an overly stiff spring. This will improve cornering grip by keeping the tire's contact patch fully on the track (rather than tilting away from the corner which would lift the inside edge of the contact patch of the outside tire). Also, anti-roll bars control the horizontal component of loading/unloading amounts from inertia in a turn.

The primary purpose of the main springs is to absorb imperfections in the track's surface - like bumps and curbs. However, they are also used to control the RATE of loading and unloading of tires from the vertical forces during acceleration, deceleration, aerodynamics and the vertical component of  loading/unloading from inertia in a turn. A secondary purpose is to control the vertical component of chassis roll. Since there is also a horizontal component of chassis roll, main springs need the help of anti-roll bars.

There are two anti-roll bars - one in the front and one in the rear of the car. Each tends to tie the suspensions on that end of the car together. For example, the front anti-roll bar ties the left front and right front suspensions together - into one unit. So, there is no control of right and left corners of the car separately - only the front control and rear control of the car.

Consider the following photographs of actual ARBs in an Indy car:

Notice that the thickness of the ARB blades is much less than the width of the ARB blades.  By rotating the blade plane from vertical to horizontal, fine adjustments of their strength can be made. Position 1 creates the softest setting and causes the blade plane to be vertical - offering less resistance to bending. Position 6 creates the stiffest setting and causes the blade plane to be horizontal - offering more resistance to bending.

It is generally accepted that it is better to reduce the stiffness, rather than increase it, to get a better handling car. Softer settings will keep lateral loading amounts more gradual, less abrupt. This will make the car "bend" into a corner, rather than "dart" into a corner. Also, softer anti-roll bars allow more lateral chassis roll in the corners, which can indirectly help with better grip capability. Of course, too much chassis roll can be detrimental, as discussed above.

Softer front ARBs will delay the loading/unloading process longer than stiffer front ARBs (and result in better grip capability but slower responsiveness at corner entry). Stiffer front ARBs will speed up the loading/unloading process more quickly than softer front ARBs (and result in reduced grip capability but quicker responsiveness at corner entry).

Anti-roll bar theory -

Anti - roll bars can affect the rate (but not change the amount) of the loading/unloading of tire contact patches in a turn. Also, the amount of lateral chassis roll needs to be controlled in order to keep the suspension geometry in "check". However, they can only control lateral (horizontal) "roll" amounts from the inertia of the car's mass throughout a turn. Acceleration, deceleration and aerodynamic forces - and the vertical "roll" amounts from the inertia of the car's mass throughout a turn - require springs and dampers to control them.

Understand that anti-roll bars cannot increase or decrease the amount of loading/unloading that occurs on a tire contact patch. However, they can temporarily absorb some of the energy created by the horizontal forces of  "weight transfer" in a turn. By decreasing or increasing the ARB arm strength, the anti-roll bar can allow the chassis to "roll" or "give" a little bit before the tire contact patch receives the load/unload amount. This, in turn, will keep the tire in proper contact with the track surface for a little bit longer. Then, after the anti-roll bar can no longer delay the process any further, the full loading/unloading of the tire contact patch will begin. This delay in the loading/unloading of a tire contact patch keeps grip in the tire for a slightly longer time - not by much, but it might be enough!

In a turn entry, delaying the unloading of the inside tire contact patches and delaying the loading of the outside tire contact patches creates another advantage. The delay in “weight transfer” from inside to outside will help turn the car more efficiently at turn entry. This delay keeps the inside tire contact patches “weighted” for a longer time.

The diameter, chemical makeup, position, etc. of the anti-roll bar arm determines how much its effective stiffness can be "fine tuned". Softer ARBs will delay the loading/unloading process longer than stiffer ARBs (and result in better grip capability). Stiffer ARBs will speed up the loading/unloading process more quickly than softer ARBs (and result in reduced tire grip capability).

The anti-roll bars can be adjusted with 4 separate, but related, items:

a. bar diameter - small (softer) or large (stiffer)

b. bar blade makeup - steel is stiffer than titanium

c. bar blade position - "1" is softest (vertical), "6" is stiffest (horizontal) and can be adjusted with in-car tools

d. ARB preload -  The ARB preload is a way to make the anti-roll bar system be asymmetric - that is, not the same roll strength on both suspensions the ARB controls. Either end of the ARB blade can be "twisted" a bit, so the inside suspension can be made stiffer than the outside suspension, and vice versa. The "twisting load" is measured as the preload amount (in ft-lbs. of force). This “twisting” is done while the car is static (in the garage), hence the name 'preload'. The ARB is quite literally preloaded with a “twisting force” on one of the two ends of the blade - usually accomplished by changing the mounting location (“drop-link position”) on that end. The "twist" produces a stiffer ARB on that corresponding half of the blade than on the "untwisted" half of the blade.

A "0" preload amount indicates there is no "twist" and that both suspensions are of the same roll strength (normal setting on a road course). A positive front preload amount indicates that the right side suspension is stiffer in roll than the left side. A negative front preload amount indicates that the left side suspension is stiffer in roll than the right side. (The rear ARB preload system is reversed).

Also, understand that although anti-roll bars cannot change the amount of loading/unloading in tire contact patches, they CAN change the amount of lateral chassis roll. A stiffer anti-roll bar will reduce lateral chassis roll - at the expense of speeding up "weight transfer" and reducing grip capability. A softer anti-roll bar will increase lateral chassis roll - but slow down "weight transfer" and give better grip capability. So, although the amount of lateral chassis roll can be changed by the strength of an anti-roll bar, the amount of "weight transfer" cannot be changed. "Weight transfer" occurs regardless.

However, too soft of anti-roll bar settings can cause too much lateral chassis roll, impact the camber of the tire and even cause the outer front corner of the car to bottom out in a corner. Conversely, too stiff of settings can result in poor handling in tight corners, with the inner tire actually lifting off the track surface.

Recall that a banked turn results in less lateral chassis roll than a flat turn. Conversely, a flat turn results in more lateral chassis roll than a banked turn. Excessive lateral chassis roll can impact the camber of a tire and reduce the tire contact patch size, creating excessive tire wear and lessen grip. For this reason, stiffer anti-roll bars are used on a track with flat turns than one with banked turns. Softer anti-roll bars are used on a track with banked turns than one with flat turns.

Also, remember that the radius and speed of a turn affect overall chassis roll. This fact may alter the anti-roll bar settings from above.

By far, the most important attribute of managing the rate of load transfer with anti-roll bars (used alongside springs) is their ability to differentially control front versus rear grip in the car. In choosing proper ARB and spring stiffness, the front grip level can be much different than the rear grip level - altering the dynamic balance of the car.

Anti-roll bar strengths on an oval -

If the oval has flat turns, both front and rear anti-roll bars are set to stiffer values than banked turns. Stiffer anti-roll bars will help limit lateral chassis roll.

If the turns are banked, horizontal “inertial influences” are reduced by the horizontal component of the force from the banked track - resulting in reduced lateral chassis roll. Both front and rear anti-roll bars are set to softer values than flat turns.

Some IndyCar engineers actually disengage the rear anti-roll bar on banked oval tracks - this illustrates how much lateral chassis roll is reduced on a banked oval. There simply isn't enough lateral chassis roll to warrant the use of a rear anti-roll bar.

Anti-roll bar strengths on a road/street course -

In general, the front anti-roll bar might be a bit stiffer than the rear anti-roll bar. A stiffer front anti-roll bar will help reduce the lateral chassis roll in the front of the car compared to the rear of the car - allowing the steering to be more responsive (at the expense of a bit less grip). Also, a softer rear anti-roll bar will help with better grip capability of the rear tire contact patches - the powered wheels. Since there is a fine line between proper chassis roll and too much chassis roll, the difference between front and rear anti-roll bar strengths will be important to consider.

If the front tires are not gripping properly and the car is sliding, rather than rotating, through corners, softening the front ARB may be one solution. In this case, the front ARB may actually be softer than the rear ARB.

So, you want to use the softest anti-roll bars as possible, but not one bit softer. There is a point where "too-soft" ARBs can make things worse. Anti-roll bars work together with main springs and dampers to control the lateral as well as vertical "roll" characteristics of the suspension. For example, using softer main springs will generally require stiffer anti-roll bar settings.

In-car anti-roll bar adjustments to control oversteer/understeer -

It has been shown that softer anti-roll bars delay "weight transfer" by slowing down the loading/unloading process of the tires - resulting in better grip capability. Stiffer anti-roll bars speed up "weight transfer" by speeding up the loading/unloading process of the tires - resulting in reduced grip capability.  Since anti-roll bar stiffness can be changed with in-car adjustments, loading/unloading of tire contact patches (and indirectly, their grip levels) can be altered while in the car.

If overall grip is an issue with all 4 tire contact patches, then symmetrically changing both front and rear anti-roll bar strengths as a unit will affect the front and rear of the car by the same amount. This allows overall grip to be controlled and "fine tuned".  Using softer front and rear ARBs together will help give better grip capability by slowing the loading/unloading process on all tire contact patches. Using stiffer front and rear ARBs together will decrease overall grip by speeding up the loading/unloading process on all tire contact patches.

This "on-the-fly" control of ARBs can be used by asymmetrically choosing opposing front and rear anti-roll bar strengths, too.  If grip is an issue with just one end of the car (and its 2 tire contact patches), each end of the car can use opposing anti-roll bar strengths. Using a slightly softer ARB on the front and a slightly stiffer ARB on the rear will indirectly create better grip capability on the front tires and reduced grip capability on the rear tires - helping to control understeer in a turn. Conversely, using a slightly stiffer ARB on the front and a slightly softer ARB on the rear will indirectly create reduced grip capability on the front tires and better grip capability on the rear tires - helping to control oversteer in a turn.

In this asymmetrical use of anti-roll bars, note that the front and rear bars work together, yet opposite each other. Soft front/stiff rear anti-roll bars help control understeer. Stiff front/soft rear anti-roll bars help control oversteer. Smaller numbered bars = softer. Larger numbered bars = stiffer.

Anti-roll bars summary -

a. anti-roll bars control the horizontal (lateral) forces and lateral chassis roll in a turn

b. for lateral forces in a turn:

- softer anti-roll bars delay "weight transfer" and slow down the rate of  lateral unloading/loading forces, slowing the rate of grip loss in tires

-  stiffer anti-roll bars hasten "weight transfer" and speed up the rate of lateral unloading/loading forces, speeding the rate of grip loss in tires

c. for lateral chassis roll in a turn:

- softer anti-roll bars increase lateral chassis roll

- stiffer anti-roll bars reduce lateral chassis roll

d. for flat versus banked turns:

- a banked turn results in less lateral chassis roll = softer anti-roll bars

- a flat turn results in more lateral chassis roll = stiffer anti-roll bars

e. for road/street course turns:

- stiffer front anti-roll bar results in less lateral chassis roll, more responsive steering, reduced grip capability

- softer rear anti-roll bar results in more lateral chassis roll, better grip capability

f. for understeer/oversteer control:

- stiffer front/softer rear anti-roll bars increases understeer (reduces oversteer)

- softer front/stiffer rear anti-roll bars increases oversteer (reduces understeer)

Anti-roll bars rule of thumb - The less a turn is banked, the stiffer both anti-roll bars should be. Flat turns require stiffer anti-roll bars. Banked turns require softer anti-roll bars. Try for as soft of anti-roll bars as possible (to delay "weight transfer" and slow the rate of grip loss). Be aware of "too-soft" anti-roll bars causing excessive lateral chassis roll. Also, on an oval, the front anti-roll bar should be a bit stiffer than the rear anti-roll bar.

2. main springs, dampers and the 3rd spring - the main springs are designed to compress under loading, then immediately rebound or expand as soon as the loading force is absent. However, springs will "overshoot" their neutral (static) state during these compression/rebound episodes - oscillating between compression and rebound until the static state is finally reached. This is the common "boing-boing-boing" motion you see in a spring. Dampers help minimize these oscillations - and can "fine tune" the main springs compression and rebound.

Consider the following diagram of a damper unit:

In an Indy Car, the damper shaft is longer and protrudes from the end of the damper unit a bit more than the diagram illustrates - to allow the main spring to wrap completely around it. It is the movement of this shaft that controls the movements of the main spring that surrounds and is attached to it. Dampers will be explained in detail below.

The 3rd spring allows for softer main springs to be used on a road/street course than without it. There are many advantages of using a softer main spring over a stiffer one. However, one disadvantage is that softer main springs might cause the car to "bottom out" under extreme pitch changes - heavy braking, heavy accelerating - or excessive aerodynamic downforce. The 3rd spring is designed to only be activated by these longitudinal (straightline) forces from accelerating, decelerating or aerodynamic downforce - and help maintain the proper ride heights. The 3rd spring will be explained in detail below.

An actual Indy Car rear suspension assembly is shown below. The front suspension assembly is similar:

Each main spring wraps around the metal shaft protruding out the rear of each damper. This assembly creates the spring/damper unit. Also, there are compression and rebound valves (seen as the circular knobs on the right side of each damper) that are used to fine tune the dampers. The valves are tuned by inserting an allen wrench into the top of each valve.

The 3rd spring (explained in detail below) is controlled by 2 control arms - one connected to each main spring. Notice that the only way the 3rd spring can be compressed is if BOTH main springs are compressed. If only one main spring is compressed, its associated control arm will move - but it will NOT activate the 3rd spring by itself.

Let's look, in detail, at each of the "players":

a. main springs and dampers - main springs are used to absorb imperfections in the track's surface - like bumps and curbs. However, they are also used to control the loading and unloading of tires from the vertical forces during acceleration, deceleration, aerodynamics and the vertical component of loading/unloading from inertia in a turn. Also, main springs work together with anti-roll bars to control chassis roll (its vertical component). Since tire grip is affected most in a turn, the bulk of the following discussion will be on main springs and their control of the car in a turn. The turn could be on a road/street course, or it could be on a high banked oval. The basics are the same, however a banked turn does create some exceptions that will be addressed.

The following is an actual vertical suspension trace for a lap around the Indianapolis Motor Speedway oval (nearly flat - bank angle of 9 degrees). The blue line is the suspension travel for the right front. The red line is the suspension travel for the left front. Similar traces are observed for the rear suspensions, too. Loading or compression (bump) movement is upward on the graph. Unloading or expansion (rebound) movement is downward on the graph:

An analysis of the graph yields some intriguing results. Notice that at the beginning of each turn, the suspensions move opposite to each other. The right front spring increases its compression amount - the left side spring increases its expansion amount. Then, both settle down and remain at nearly constant amounts of compression or expansion. At the start of the exit of each corner, again the suspensions move in opposite directions. This time, the right side spring increases its expansion amount - the left side spring increases its compression amount.

Notice, too, that the amounts of compression/expansion are greater for the right front than the left front spring. Also, on the straights, nearly constant amounts of compression/expansion are observed.

Similar results can be found for the rear suspensions.

Now, consider the following vertical suspension trace for 2 laps around the Texas Motor Speedway (bank angle of 24 degrees). The spring strengths were the same as the ones used in the previous trace for a flat oval:

Compare this trace with the one above from a track with flat turns. An analysis of the graph shows just how much a banked turn can alter suspension movements and associated loading forces. The right front spring still compresses/expands more than the left front spring. But, notice how much more the right front spring compresses/expands than the same right front spring on the flat turn - about 10 mm more.

Also, the left front spring shows very little compression/expansion - especially compared to the same left front spring on the flat turn.

Similar results can be found for the rear suspensions.

Now, consider a general lap around an oval race track - specifically, how the suspensions react to the loading/unloading of tire contact patches. Since we are analyzing vertical loading/unloading amounts, the discussion will focus solely on main springs.

On the straights, the car is in balance. All 4 corners of the car are at optimum ride heights. All 4 tire contact patches are at their optimum - downforce levels have been adjusted to give the contact patches proper grip levels. Suspensions are in a neutral (static) state - all are compressed from downforce, but are not changing in compression/expansion amounts. "Weight transfer" is not occurring, because there are no “inertial influences” acting on the car while it is at a constant speed along the straight. So, there is no loading or unloading of the tire contact patches from “weight transfer”. All 4 corners of the car are in balance.

At the instant the car enters a turn, forces begin to alter the car's balance. The forces (other than friction) acting on the car in a turn are from: 1) the transition between the straight and the banking in the corner (unless the corner is completely flat); 2) cornering of the car and its associated inertia (causing the car's chassis to roll to the outside of the turn); 3) decelerating into the corner and accelerating out of the corner; and 4) banking (if it exists). Some of these forces are actually destructive to others. For example, the banking will cause the inside suspension to compress, partially negating the expansion of the inside suspension from roll inertia. Other forces can actually be constructive to others. For example, that same banking will cause the outside suspension to compress, adding to the compression of the outside suspension by roll inertia. However, the NET result of all of these forces cause the inside suspensions to expand (rebound) and the outside suspensions to bump (compress) at the entrance to the turn.

The car is now out of balance. The inside tires have begun to unload more than normal. The outside tires have begun to load more than normal. Grip is beginning to be compromised.

At some point, very early in the turn, the unloading/loading causes the lack of grip to become critical. When the tires reach their limit of adhesion, they will slip.

After the initial loading/unloading phase, throughout the turn, the outside suspensions retain their compression and the inside suspensions retain their expansion. The initial entry into the turn increased expansion on the inside and increased compression on the outside suspensions. After this initial movement, all 4 suspensions retain the maximum amount of expansion/compression throughout the turn - until corner exit. So, from corner entry, throughout the apex of the corner, to corner exit, the car is imbalanced. The inside tires have been excessively unloaded. The outside tires have been excessively loaded. This situation is referred to as "weight transfer" from the inside to outside tires.

At the onset of the exit to the turn, the outside suspensions begin to expand back to normal, causing the outside tires to unload their excess load. The inside suspensions begin to compress back to normal, causing the inside tires to reload their excess unload.  The "weight transfer" goes from the outside tires to the inside tires. Suspensions return to their neutral state. The car is now back in proper balance. Grip has been returned to the 4 tire contact patches.

In all phases of a turn, however, the outside suspensions compress/expand more than the inside suspensions. At turn entry, the outside suspensions compress more than the inside suspensions expand. At turn exit, the outside suspensions expand more than the inside suspensions compress.  

In general, a flat turn will load/unload the outside tire contact patches more than the inside tire contact patches. So, in a flat turn, the outside springs compress/expand more than the inside springs expand/compress.

Also, a banked turn will load all 4 tire contact patches more than a flat turn. That means that the outside tire contact patches load more and the inside tire contact patches unload less – than in a flat turn. So, in a banked turn, the outside springs compress/expand more than in a flat turn. And, the inside springs expand/compress less than in a flat turn.

"Weight transfer" can be controlled by the location of the center of gravity (lower is better) and the rate at which the load is transferred to the tires. Springs cannot change the load amounts, but they can impact how much the suspension moves in response to the load - and dampers can "fine tune" how fast the load transfers to the contact patches of the tires.

Spring theory -

Springs can affect (but not change the amount of) the loading/unloading of tire contact patches in a turn. Also, the amount of vertical chassis roll needs to be controlled in order to keep the suspension geometry in "check". However, they can only control the vertical "roll" amounts from the inertia of the car's mass throughout a turn.

Springs are rated by their strength - specifically, how much force (in pounds) is required to compress the spring by one inch. The force could be caused by inertia from the car's mass, weight, force from the track surface (bumps, curbs, banking, etc.) and even from aerodynamic downforce. So, a 2500 lb spring requires 2500 lbs of force to compress it by one inch. In fact, even on a high speed oval, springs compress no more than an inch. So, all of what follows below is written to understand (and maximize the efficiency of) an inch of spring travel!

Understand that a spring cannot increase or decrease the amount of loading/unloading that occurs on a tire contact patch. However, a spring can temporarily absorb some of the energy created by the vertical forces of "weight transfer" - storing it as potential energy. By compressing or expanding, the spring can allow the chassis to "roll" or "give" a little bit before the tire contact patch receives the load/unload amount. This, in turn, will keep the tire in proper contact with the track surface for a little bit longer. Then, after the spring can no longer compress or expand any further, the full loading/unloading of the tire contact patch will begin. This delay in the loading/unloading of a tire contact patch keeps grip in the tire for a slightly longer time.

In a turn entry, delaying the unloading of the inside tire contact patches and delaying the loading of the outside tire contact patches creates another advantage. The delay in “weight transfer” from inside to outside will help turn the car more efficiently at turn entry. This delay keeps the inside tire contact patches “weighted” for a longer time.

Softer front springs will delay the loading/unloading process longer than stiffer front springs (and result in better grip capability but slower responsiveness at corner entry). Stiffer front springs will speed up the loading/unloading process more quickly than softer front springs (and result in reduced grip capability but quicker responsiveness at corner entry).

Analyzing how "weight transfer" is affected in a race track's turn, and looking at the previous suspension trace graph, some conclusions can be drawn about springs:

1. from corner entry, through the apex of the corner, until corner exit - inside tires unload, outside tires load. A softer-than-normal spring will temporarily absorb some the energy from the forces causing the "weight transfer" from inside to outside. This will keep the tires in proper contact with the track surface longer, slow the rate the car will become imbalanced - and delay the loading/unloading process.

2. from corner exit until the straight - inside tires load, outside tires unload. A stiffer-than-normal spring will not absorb as much energy from the forces causing the "weight transfer" from outside to inside. This will return the car more quickly to a balanced condition - and, speed up the loading/unloading process.

So, a softer spring is desired for corner entry until corner exit. At corner exit, a stiffer spring is desired. Unfortunately, springs cannot be changed in mid-corner, so a compromise needs to be made in the choice of spring strength. The damper affecting a spring will be able to "fine tune" it and effectively make it "act" stiffer-or-softer-than-normal when needed.

Spring strengths on an oval - 

Ovals present a unique look at the loading/unloading of tires (and the associated "weight transfer"). There is asymmetry involved, since the left side suspension acts much differently than the right side suspension. This asymmetry can allow for some interesting spring settings - taking advantage of the knowledge about left-hand-only turns.

On an oval, springs are set to a higher (stiffer) value on the right wheels and a lower (softer) value on the left wheels. This is due to left-hand-only turns - recall that outside suspensions compress/expand more than inside suspensions expand/compress in a turn. So, right side tire contact patches load/unload more than left side tire contact patches in a left-hand turn. Also, the right front wheel requires the stiffest spring and the right rear wheel requires a slightly softer spring.

If the turns are banked, the excess loading of all 4 tire contact patches and increase in “centripetal force” can be controlled with a decrease in aerodynamic downforce. In a banked turn, the inside suspensions expand/compress much less than the outside suspensions - if at all. So, on a banked oval, springs can be quite soft on the left wheels. The amount, however, is determined by the bank angle.

Spring strengths on a road/street course -

Road/street courses have about as many right-hand turns as left-hand turns. So, any advantage of using unique settings for a left-hand turn are negated by a right-hand turn. Symmetrical use of both front and both rear spring strengths will be used.

Typically on a road course, springs are symmetrically set to a higher (stiffer) value in both front wheels (for better vertical chassis roll control - at the expense of reduced grip) and a lower (softer) value in both rear wheels (better grip capability and traction for the powered wheels). Stiffer springs create more attitude control and less vertical chassis roll in a corner. Softer springs create better mechanical grip. Also, stiffer front springs are used on high speed, smooth tracks and softer front springs are used on slower speed, bumpy tracks.

In higher speed courses (where aero downforce pushes the car down more than on a slower speed course), stiffer springs will keep the car from bottoming out, allowing lower ride heights than with softer springs. However, softer springs can be augmented with the use of the 3rd spring. Choosing the right spring strength is a compromise and found with a lot of testing - and thought and analysis.

Also, understand that although springs cannot change the amount of loading/unloading in tire contact patches, they CAN change the amount of vertical chassis roll. A stiffer spring will reduce vertical chassis roll - at the expense of speeding up "weight transfer" and reducing grip capability. A softer spring will increase vertical chassis roll - but slow down "weight transfer" and give better grip capability. So, although the amount of vertical chassis roll can be changed by the strength of a spring, the amount of "weight transfer" cannot be changed. "Weight transfer" occurs regardless.

However, too soft of spring settings can cause too much vertical chassis roll, change the suspension geometry, impact the camber of the tire and cause excessive tire wear.

So, you want to use the softest springs as possible, but not one bit softer. There is a point where "too-soft" springs can make things worse.  Keep in mind that any amount of damping (see discussion below), even the minimum, will slow down the speed of the spring's compression/expansion. So, damping will effectively create a spring that reacts a bit "stiffer" than its actual strength.

If rear wheel spin is an issue (from excessive throttle input), especially out of a slow speed corner, a softer rear spring may help with better rear grip capability. Additionally, a softer front spring can decrease an understeer condition in a corner.

By far, the most important attribute of managing the rate of load transfer with springs is their ability to differentially control front versus rear grip in the car. In choosing proper spring stiffness, the front grip level can be much different than the rear grip level - altering the dynamic balance of the car.

Main springs summary -

a. main springs control the vertical forces and vertical chassis roll in a turn (as well as bumps and curb hits)

b. for vertical forces in a turn:

- softer springs delay "weight transfer" and slow down the rate of vertical unloading/loading forces, slowing the rate of grip loss in tires

-  stiffer springs hasten "weight transfer" and speed up the rate of vertical unloading/loading forces, speeding the rate of grip loss in tires

c. for vertical chassis roll in a turn:

- softer springs increase vertical chassis roll

- stiffer springs reduce vertical chassis roll

d. for flat versus banked turns on an oval:

- a banked turn increases vertical loading of all 4 tires and more “centripetal force” = less aerodynamic downforce

- a banked turn creates more outside spring movement, very little (or none) inside spring movement = stiffer outside springs, very soft inside springs

 - bank angle determines spring strength amounts

 - a flat turn creates more outside spring movement, less inside spring movement = stiffer outside springs, softer inside springs

e. for road/street course turns:

- stiffer front springs on both wheels results in less vertical chassis roll, more responsive steering

- softer rear springs on both wheels results in more lateral chassis roll, better grip capability

Main springs rule of thumb - On an oval, right side springs are stiffer than left side springs. And, the right front spring is the stiffest. If the oval has banked turns, left side springs are quite soft. Try for as soft of springs as possible (to delay "weight transfer" and slow the rate of grip loss). Be aware of "too-soft" springs causing excessive vertical chassis roll.

On a road/street course, both front springs are stiffer than both rear springs. And, both front springs have the same strength; both rear springs have the same strength.

Damper theory -

Dampers can control compression (bump)/expansion (rebound) speeds in the main springs. Front springs will compress under braking, while rear springs will expand. Also, front springs will expand during acceleration, while rear springs will compress. If a bump or curb is hit, the springs will oscillate wildly between compressing and expanding. Dampers can control how much and how quickly compression and rebound occurs in the springs as they expand or contract.  They quite literally "dampen" the speed at which the springs oscillate - in physical terms, dampers slow down the frequency of the springs' oscillations.

Without dampers, the main springs would effectively keep bouncing up and down, until the potential energy stored in the springs is dissipated. An undamped spring would also overshoot its compression and expansion points. Dampers help to dissipate any vertical movement in the suspension and keep the spring movements controlled. Also, they can "fine tune" the rate at which the tire is loaded/unloaded with forces from braking, accelerating and cornering - helping keep each tire in optimal contact with the track surface.

IMPORTANT POINT: A spring with NO damping will have no attenuation of its compression/expansion speeds. Adding ANY amount of damping will slow down that rate of compression/expansion. The minimum amount of damping available will slow down the speed by the LEAST amount possible. The maximum amount of damping available will slow down the speed by the MOST amount possible. It is a bit of a misnomer, then, to say that less damping will "speed up" a spring's compression/expansion speed. It won't speed up something that cannot be sped up any faster! By its nature, a spring with NO damping whatsoever has as fast of a compression/expansion speed as possible.

Just like springs, dampers don't limit the total load levels to the tires, but they do affect the speed of  how fast the suspension reacts to these load changes and how fast the tire's contact patch receives these loads. The ability of dampers to affect the amount of time it takes for the loads to the tires to transfer is important. A damper cannot reduce these loading/unloading forces, but it can control how fast or slow those forces transfer to the tire's contact patch with the track surface.

The damping force (strength) a damper provides is proportional to velocity. So, the faster the main spring compresses or expands, the larger the damping force. Conversely, the slower the main spring compresses or expands, the smaller the damping force. In other words, when a damper is compressed or extended slowly, the resulting resisting force from the damper will be smaller than when it is compressed or extended faster. Since a damper is basically a piston in a tube filled with hydraulic oil, it can create damping forces at a variety of different strengths. Simply put, the faster the damper piston is pushed or pulled, the more damping force the damper produces. Although the damper can react to an almost infinite amount of spring compression/expansion speeds, there are typically 2 broad classes of speeds the damper will need to react to on a race course. Relatively slow motions of the springs (which are driver controlled as in accelerating, decelerating and turning) occur on smooth sections of the track and create smaller damping forces. Extremely fast motions of the springs (which are road controlled as in bumps and curbs) occur on bumpy sections of the track and create high damping forces. These forces can be so high that the damper chamber might explode if not for a popoff valve.

 Therefore, there are really only 2 thresholds of speed the dampers will experience on a race track: low speed (piston velocities less than 1 inch/second) and high speed  (piston velocities greater than 1 inch/second up to 10 inches/second) - and they serve two very different purposes.

Low speed damping is used with smooth surfaces (from accelerating, decelerating and cornering loads causing the main spring to compress or expand relatively slowly). Generally, the low speed range of the damper (0 - 1 in/sec) will influence the transient handling of the car when it is subjected to driver-created forces from acceleration, deceleration and cornering.

High speed damping is used with bumpy surfaces (and have nothing to do with the actual speed of the car - the 'speed' here is how fast the damper moves in compression or rebound;  i.e. damper piston velocities). Generally, the high speed range of the damper (1 - 10 in/sec) will influence the response of a car to road-created forces from bumps and curb hits.  

Each damper has 2 components: a compression (bump) component and an expansion (rebound) component. So, each corner of the car is controlled by a total of 4 damper settings - low speed bump, low speed rebound, high speed bump and high speed rebound.

Damper settings can be adjusted with valves, allowing more or less damping force for each of the bump and rebound values. The more the damping force is, the slower the associated spring will compress or expand. The less the damping force is, the faster the associated spring will compress or expand. This, in turn, will affect the speed at which the spring moves. Since each damper has the ability to affect both compression and expansion speeds of the associated spring - and by completely differing amounts, the rate of loading can be different than the rate of unloading for each tire contact patch. In this way, the effective strength of the spring can be changed without ever physically changing the spring itself.

Let's look, in more detail, how dampers control the rates of compression and expansion of the springs and how that affects the rate of loading/unloading of the tires. Keep in mind that the contact patches of the tires with the track surface need to be kept as consistent as possible. As the car accelerates, decelerates, turns or hits bumps, those contact patches are constantly changing. Dynamic "weight transfer" is occurring throughout this entire process (due to the “inertial influences” described previously). Tires are being loaded and unloaded each time the car speeds up, slows down, turns or hits a bump, curb, etc.

Suppose a spring compresses. The tire will load in response to the force causing the compression. How fast the loading occurs is controlled by the corresponding spring and damper. This is where tuning of the damper strength comes into play. A stiff ("more") damper compression setting will speed up the loading process of the tire. A soft ("less") damper compression setting will slow down the loading process.

Now, suppose a spring rebounds. The tire will unload in response to the force causing the expansion. How fast the unloading occurs is controlled by the corresponding spring and damper. A stiff ("more") damper rebound will speed up the unloading process. A soft ("less") damper rebound will slow down the unloading process.

This is why dampers are considered "fine tuning" adjustments for springs. Both springs as well as dampers can control the rate of loading/unloading. But, a spring cannot change its strength level. However, a damper can change its strength level between bump and rebound settings - allowing for the spring to be "fine tuned". Basically, more damping will allow a spring to "act" stiff when it needs to be. Less damping will allow a spring to "act" soft when it needs to be.

In review, more damping will speed up the loading/unloading of a tire. Less damping will slow down the loading/unloading of a tire. And, having separate bump and rebound settings on each damper allows them to "fine tune" the corresponding springs they control. It should be noted, however, that excessively soft or stiff damper settings can produce the exact opposite effects. So, damper settings need to be set within limits.

Consider the following situations with damping:

1. more damping during compression (bump) - this will slow down the spring's compression (and the damper's piston compression will be slower). So, the load will transfer to the tire more quickly because it is taking the spring longer to absorb some of the loading force - and speeding up the tire's ability to be pushed into the track surface. Basically, the damper is "clamping" down on the spring more than normal, slowing its ability to compress. If the spring can't compress as fast, it can't do its job as fast, causing the load to "get" to the tire faster. Think in these terms if that sounds counter-intuitive: If there was INFINITE damping, then the spring would not compress at all. The spring's compression speed would be ZERO. So, the load would transfer to the tire immediately.

2. less damping during compression (bump) - this will speed up the spring's compression (and the damper's piston compression will be faster). So, the load will get to the tire more slowly because it is taking the spring less time to absorb some of the loading force - and slowing down the tire's ability to be pushed into the track surface. If the spring can compress faster than normal, it can do its job faster, absorb some of the loading force faster, and cause the load to "get" to the tire slower . Think in these terms if that sounds counter-intuitive: If there was ZERO damping, then the spring would compress with no resistance whatsoever. So, the load would transfer to the tire only after the spring was finished compressing. The load would transfer to the tire slowly.

3. more damping during expansion (rebound) - this will slow down the spring's expansion (and the damper's piston expansion will be slower). So, the load will transfer away from the tire more quickly because it is taking the spring longer to extend - and speeding up the tire's ability to be lifted from the track surface. Basically, the damper is "clamping" down on the spring more than normal, slowing its ability to expand. If the spring can't expand as fast, it can't do its job as fast, causing the load to "escape" from the tire faster. Think in these terms if that sounds counter-intuitive: If there was INFINITE damping, then the spring would not expand at all. The spring's expansion speed would be ZERO. So, the unloading of the tire would occur immediately.

4. less damping during expansion (rebound) - this will speed up the spring's expansion (and the damper's piston expansion will be faster). So, the load will transfer away from the tire more slowly because it is taking the spring less time to extend - and slowing down the tire's ability to be lifted from the track surface. If the spring can expand faster than normal, it can do its job faster, and cause the load to "escape" from the tire slower . Think in these terms if that sounds counter-intuitive: If there was ZERO damping, then the spring would expand with no resistance whatsoever. So, the load would transfer away from the tire only after the spring was finished expanding. The load would transfer away from the tire slowly.

Low speed/high speed damping on ovals -

Low speed damping on an oval is usually limited to matching damping strength to spring strength.  Cornering forces and their associated loading and unloading are much smoother and less abrupt than on a road course. Although the concept of delaying weight transfer is important on an oval, there isn't the quick left-right cornering with large changes in speed. So, low speed damping is of less importance. Using more damping on softer springs and less damping on stiffer springs is usually sufficient "tweaking". However, there will be asymmetrical settings used for the left and right side dampers - just as there are for the associated springs.

High speed damping will occur if there are bumps on an oval track surface. However, they will not impact the ability of the car to turn better (or worse) in a corner. High speed damping, though, can affect the tire contact patch as a tire hits a bump. Both high speed compression damping as well as high speed rebound damping occurs when a bump is hit - even on an oval. The spring strengths chosen to manage cornering loads may not be the best to handle bumps and curbs in the track surface. But, those springs can be "fine tuned" with the high speed bump and rebound damper settings.

With high speed damping, the time each tire spends in "bump mode" should be the same as the time spent in "rebound mode". Simply put, a tire that hits a bump in the road should spend equal amounts of time going up as going down! Managing low speed damping (for attitude control in a corner) and high speed damping (for bump hits) can be analyzed via telemetry software, such as Motec i2.

Low speed/high speed damping on road/street courses -

Since road/street courses have both right and left hand turns and street courses can be pretty bumpy, we will consider both low speed as well as high speed damping. Also, both front two tires will have the same damping settings. And, both rear two tires will have the same damping settings. However, this "perfect symmetry" between the left and right side damping amounts may need to be fine tuned. More about that possibility below. This symmetrical use of damping will be used on road/street courses - since turns are both left and right hand. The asymmetrical settings from the previous discussion on ovals (and their left-hand only turns) will not be used on road/street courses. A right hand turn would simply negate the special settings for a left hand turn.

Low speed damping can be used to fine-tune the main springs during transient cornering. Grip issues can be dealt with by altering the rate of transfer of the load to certain tires. Knowing whether a spring is in bump or rebound on a particular suspension and tire in question can help determine the associated damper settings. Through analysis of what each tire is doing in a corner, adjustments can be made to the low speed dampers. This possibility allows for myriad options. Using the ideas from the previous discussion on delaying weight transfer to a tire, mixing and matching bump and rebound low speed dampers can “fine-tune” grip levels. Difficult understeer/oversteer issues in a corner may have a solution found in changing bump or rebound low speed dampers on one or more springs.

High speed damping will occur if there are bumps on the track surface. However, they will not impact the ability of the car to turn better (or worse) in a corner. High speed damping, though, can affect the tire contact patch as a tire hits a bump. Both high speed compression damping as well as high speed rebound damping occurs when a bump is hit. The spring strengths chosen to manage cornering loads may not be the best to handle bumps and curbs in the track surface. But, those springs can be "fine tuned" with the high speed compression and rebound damper settings.

With high speed damping, the time each tire spends in "bump mode" should be the same as the time spent in "rebound mode". Simply put, a tire that hits a bump in the road should spend equal amounts of time going up as going down! Managing low speed damping (for attitude control in a corner) and high speed damping (for bump hits) can be analyzed via telemetry software, such as Motec i2.

Analyzing damper velocities -

The goal, of course - whether on an oval or road/street course, is to keep the four tire contact patches on the track surface for as long as possible, without too much load or too little load. In other words, we want all four tire contact patch loads to have as little variation as possible. Since a road/street course has about the same number of right and left turns and bumps are pretty well randomly distributed, there should be about as much time spent in compression damping as rebound damping for each of the front pair and rear pair of contact patches - both for low speed as well as high speed damping. On an oval, only left hand turns are navigated. Each corner of the car will have unique damping characteristics and front pair and rear pair contact patches will be unique - as described previously. However, overall, the time spent in being loaded should be offset by the time spent in being unloaded (for each tire) - regardless of an oval or road/street course. That way, the unwanted loading/unloading forces will be optimized.

For example, suppose one corner of the car spends more time in high speed compression than high speed rebound damping. That is a fancy way of saying that the wheel spends more time going down than going up from a bump hit! Then, that tire spent too much time being loaded. In this case, high speed compression damping needs to be made FASTER (with LESS high speed compression damping), so the loading time is reduced.

Time spent in compression (bump) and rebound for each tire contact patch can be evaluated by examining the "Damper Velocity Histogram" for each damper. The goal is to adjust compression times against rebound times until each histogram is symmetrical (or close). These histograms are available in telemetry software, such as Motec i2.

When a tire passes over a single bump in the track surface, there is initially an amount of positive damper velocity as the bump is hit. The damper is compressed. This is immediately followed by an amount of negative damper velocity as the tire passes over the bump. The damper is extended. To maintain balance on this corner of the car (and keep from having an imbalance in the amount of loading and unloading of the tire), positive and negative damper velocities should be as close as possible in magnitude and duration. This symmetry will minimize the tire contact patch variations.

Now, picture the above single bump hit for an entire lap around the track, where the dampers will react to thousands of bumps varying in magnitude. Additionally, there will be the low speed damping effects from inertial forces of acceleration, deceleration and cornering. If the chassis is balanced properly, the suspension will dissipate equal amounts of energy in bump and rebound movements. This balance should result in symmetrical damper velocity histograms for all four corners of the car.

Unfortunately, the real world is not so perfect. More bumps may be hit on the left side than the right side. On a road/street course, there may be more left hand turns than right hand turns. The result of a real world track and its forces may lead to asymmetrical damper usage. Fine tuning each corner may need to occur, so the front wheels "match" each other and the rear wheels "match" each other. This "match" may actually lead to a small difference in damping amounts. For example, more bumps on one side of the car may change the amount of high speed compression or rebound damping on that side. So, although the damper velocity histograms may look the same and "match", the left and right side damping amounts may be slightly different.

Consider the following damper velocity histogram for one corner of the car:

Notice that high speed damping is symmetrical (pink area)- there is about as much time spent in bump as in rebound. Now look at low speed damping (red area). There is more time spent in low speed bump than in rebound (but not by much) - noticed because the red area to the right of the dotted line is bigger than the red area to the left of the dotted line. To solve this imbalance, the amount of time spent in low speed bump needs to be less (or the time spent in low speed rebound needs to be more). So, low speed bump needs to be faster (less low speed bump damping) or low speed rebound needs to be slower (more low speed rebound damping). This change will make the histogram more symmetrical - and this corner's tire contact patch will have as little variation in loading/unloading as possible.

Underdamping and overdamping can have negative effects, too. Consider the following cases:

Bump component - 

During bump, the dampers and springs absorb the upward movement from cornering or road irregularities (the springs store some of it as potential energy), then the dampers go into rebound. If there isn't enough damping then the cycle repeats again until the car returns to the original ride height, with a bouncing motion to the car. Another trait of under damping is that loads go into the tire and suspension relatively slowly - this combined with the bouncing effect means a constant varying download force. Acceleration, braking or cornering in this state will also vary due to the various download rates, so it is important to have enough bump stiffness to be able to deal with these conditions.

However, if there is too much bump damping, then it is effectively like running no suspension and any forces will be transmitted directly to the chassis.  Over damping will result in an increase in the loads acting on the suspension and the tires. The handling will feel very harsh and hard. This is undesirable in both under and over damping settings as it will reduce the handling of the car and will affect acceleration, braking and cornering loads.

Rebound component -

During rebound (following the bump compression phase) the dampers extend back to their original positions, using up the released kinetic energy from the springs. The rebound stiffness needs to be set at a higher value than the bump setting as the excess stored energy is being released. If there is not effective damping on the rebound, the wheel will quickly return through the static level and start to bump again, with the bouncing effect unsettling the suspension with little control.

 However, if there is too much rebound damping, then the wheel could be delayed from returning its contact patch fully to the track surface - effectively, losing contact with the road as the force to push the wheel back down is slower to respond to the changing surface level. This will create less than optimal tire contact with the road.

So, what should be the setting for all 16 damping options in the car?? Not all dampers are used equally at a given track (Indy road course, for example, is as smooth as a billiard ball - high speed damping is not part of the equation here; Long Beach is bumpy - high speed damping is VERY important).  Also, all road courses have some braking/accelerating in a straight line (where all low speed damping may be in effect simultaneously).  And, most road courses have smooth sections and bumpy sections. It seems that there are so many options and combinations of which damping is used in a given situation, there is no magic formula.  However, softer springs require more damping. Stiffer springs require less damping.

In the iRacing garage, in 'Dampers' section, you will see the 16 total damping settings listed. Very confusing negative 'click' numbers are used to show the amount and stiffness of the dampers. Rather than attempt to figure out the negative values and what they mean, use this rule of thumb:

use the right arrow  -->  to INCREASE  (more) damping - i.e., stiffer

use the left arrow   <--   to DECREASE  (less)  damping - i.e., softer

NOTE: As with all negative numbers, -20 is a smaller number than  -15. So, a damping value  of -20 clicks is  LESS damping than -15 clicks. Conversely, -5 is a larger number than -10, so a damping value of -5 clicks is MORE damping than -10 clicks. THE BIGGER THE NUMBER, THE MORE DAMPING YOU HAVE SELECTED.

To put it in simpler terms, the more negative clicks you have "clicked on" (by using the left arrow), the less damping you have selected.  The fewer the negative clicks you have "clicked on" (by using the right arrow), the more damping you have selected. So, -20 clicks has 5 more clicks you "clicked on" than -15 clicks does, so -20 clicks has LESS damping than -15 clicks. Also, -10 clicks has 7 fewer clicks you "clicked on" than -17 clicks does, so -10 clicks has MORE damping than -17 clicks. Dang those negative numbers!! Remember, THE BIGGER THE NUMBER, THE MORE DAMPING YOU HAVE SELECTED.

For example, suppose the front springs are initially set to 1700 lbs and rear springs are set to 900 lbs. Also, suppose the corresponding  low speed compression (bump) damping is initially set to about -15 clicks in the front and about -7 clicks in the rear. Now, if the front springs need to be stiffer, suppose they are reset to 1900 lbs. Then, the corresponding damping would need to be decreased and reset to values that are slower (less) than -15 clicks; perhaps to -17 or -18 clicks. Also, suppose the rear springs need to be softer, say 800 lbs. Then, the corresponding damping would need to be increased and reset to values that are faster (more) than -7 clicks; perhaps to -4 or -5 clicks. Similar changes would need to be made for all 16 damping settings.

Moral of the story about springs and dampers?  If you change a spring strength from a current setup, you will need to change the corresponding dampers for that spring. Stiffer spring = decrease damping. Softer spring = increase damping.

b. 3rd spring - each pair of front and rear main spring suspension assemblies includes a 3rd spring, but it is only used on road/street courses. On an oval, there isn't massive braking and accelerating  - and aerodynamic downforce levels remain fairly constant. So, a 3rd spring is unnecessary.

The 3rd spring is a stiff spring that compensates for the desire of using soft main springs for cornering as well as bumps and curb hits, without having to raise ride heights. It will only activate during extreme pitch changes - heavy braking, heavy accelerating - or excessive aerodynamic downforce, precisely when ride heights can be compromised. In a turn (or over a bump or curb hit), the softer main springs will be active. The 3rd spring will be inactive. It is only when extreme pitch changes occur or aero forces are at a maximum that the stiffer 3rd spring will be active - keeping the car from "bottoming out".

Advantages of using softer main springs have already been discussed. However, one disadvantage of using softer main springs is the potential for "bottoming out" under heavy braking, heavy accelerating or excessive aerodynamic downforce - in a straight line before or after a turn. Normally, a road/street course turn doesn't exhibit these extreme forces. You aren't slamming on the brakes in mid-corner, for example. They occur only on the straightaways. Also, using a softer spring to combat bumps and curb hits means the car's suspension is more susceptible to these compression and rebounding forces. For example, with a high aerodynamic downforce setup and soft springs, the car's suspension may be compressed to the point that the underside bottoms out on the track surface.

It is important, then, to distinguish between a car in a turn (or over a bump or curb hit) and a car on a straightaway. If the stiffer 3rd spring could be made to only activate due to longitudinal (straightline) forces, then the softer main springs could be used by themselves in turns or bumps or curb hits. This is the purpose of the control arms.

Look again at the following photograph of an actual Indy Car suspension:

Notice that the 2 control arms attach separately to each main spring, then come together at the rear of the assembly - where the 3rd spring is located. If one main spring is compressed (or expanded), then the associated control arm moves - but not the other one. Only if BOTH main springs are compressed (or expanded) will BOTH control arms move, causing the 3rd spring to activate.

This is precisely what distinguishes a car from being in a turn (or over a bump or curb hit) or on a straightaway. Forces on a straightaway will compress (or expand) BOTH main springs together (either both front or both rear main springs). Forces in a turn will not. Bumps and curb hits will not. So, the control arms will dictate whether the 3rd spring activates. It only activates when both main springs reach a critical compression point (called the 3rd spring gap). As soon as both main springs compress to that point, the 3rd spring is activated and adds additional support as a main spring compression (“bump”) stop - but only at that critical point and beyond . In this way, you can use softer main springs yet have the luxury of a stiffer spring when needed - utilizing the best of both worlds.

You will see the "3rd spring" listed in the iRacing "Garage", in "Chassis", under "Front" and "Rear" (there are 2 of them located in the end of the front and rear suspension assemblies). With the addition of the 3rd spring in the front and rear suspension units on a road/street circuit, you can lower the stiffness of both front main springs to around 1200 to 1700 lbs. Likewise, both rear main springs can be lowered to around 700-1000 lbs.

Since the 3rd spring allows for softer main springs, yet still allowing for lower ride heights, the question becomes when to have the 3rd spring "kick into action", so to speak. How much should both main springs compress before the 3rd spring "takes over"? You could lower the ride height and lessen the 3rd spring gap - or you could raise the ride height and increase the 3rd spring gap. Which one is the best option to use?

An Indy car engineer told me to go small for a 3rd spring gap. There are many reasons, but the ability to lower ride heights with a small 3rd spring gap is most important.

Consider the following ride height data traces from 2 different 3rd spring gap options. The first trace uses a 3rd spring gap of 0.8 inches in both the front and rear. The second trace uses a 3rd spring gap of only 0.07 inches in both the front and rear. Both traces are for one lap at Sonoma Raceway:

Notice that the variation between maximum and minimum ride heights for a 3rd spring gap of 0.8 inches is about 3 inches. With a 3rd spring gap of 0.07 inches, that variation is reduced to about 2 inches - a full 1 inch less.

More importantly, notice the average ride heights in the two traces. The average ride height using a 3rd spring gap of 0.8 inches is about 1.5 inches, while the average ride height using a 3rd spring gap of 0.07 inches is reduced to about 1.0 inches - a full 0.5 inches less. That is significant - lower ride heights mean more downforce from the underwing.

Using the 3rd spring is a compromise - in the front as well as the rear. Main springs can compress by about 1 full inch under road/street course loading. Obviously, the softer main spring needs to be used as much as possible before the 3rd spring takes over. But, at some point, ride heights need to be raised if the softer main springs are used too long in a compression event. It seems the best compromise is to allow the 3rd spring to be released after about 0.030 to 0.100 inches of main spring compression. It is better to err on the smaller size gap than the larger size gap. A smaller size 3rd spring gap will keep the suspension from cycling back and forth between the main springs and 3rd spring too often during pitch changes.

One final word about the use of a rear 3rd spring. During acceleration out of a corner, the rear 3rd spring keeps the "squatting" of the rear of the car to an absolute minimum. This allows for a very low ride height in the rear (compared to the higher ride height required without the use of a rear 3rd spring). A lower ride height means more downforce is produced from the underwing of the car. More downforce means more grip from the rear tires - crucial on corner exit. In some cases (using an extremely small rear 3rd spring gap) the ride height can be lowered more than a half inch than without the use of a rear 3rd spring - greatly increasing the rear downforce and rear grip level.

See the photo below of a front suspension assembly. The 2 main springs are at the top of the photo. The 3rd spring is located just below them. Also, the nut on the bolt between the main springs and 3rd spring is used to adjust the 3rd spring gap. Notice there is a single 3rd spring to control 2 main springs:

Remember: softer main springs allow the suspension to compress and expand more easily to the track surface conditions and "inertial influences" on the corners. This will help maintain the maximum tire contact patch size as well as keep the tire from having to do too much work. The net result will be better tire grip in the corners, where the forces are at their extremes.  However, too soft of a spring can have negative effects on grip, too. If the car's balance is upset by accelerating, decelerating and cornering, a stiffer spring will help neutralize those forces. This is why it is said to "use as soft of a spring as possible, but not one bit softer". You must try different spring strengths. Start with stiff spring values in each corner. Then, begin to soften each corner's spring, and see what effect it has on tire wear, tire temperature (by investigating the tire data) and consistency of lap times over a longer run. Keep on trying different spring strengths and ARBs. It takes time and a bit of effort, but in the end you will have a faster Indy Car. It is quite literally a balancing act you will need to perform - a mechanical balancing act.