General IndyCar Open Setup Basics - 4
Open setup primer for road/street circuits
In my previous 3 primers, terms and uses were introduced for setting up the DW12 and IR-18 IndyCar. Although all of the information is pertinent to oval as well as road/street setups, there are some new terms and philosophies that need to be addressed. These are not new or necessarily specific to road/street courses, but they were not discussed before. In most of the cases, these new concepts were handled very well in the fixed setups we used as baselines in our oval setups. They were either a very minor issue, or were already given values that were appropriate and sound - by the baseline fixed setups that were our starting points.
In road/street courses, the speeds are much lower and the car is set up symmetrically since there are right hand turns as well as left. In an oval setup, aero grip dominates because wings are so effective. Also, asymmetry of the car is used - more tire pressure on the right side tires, higher ride height and stiffer springs on the ride side suspension and so on. On road/street courses, decreased speeds mean that the aero grip produced by wings is massively reduced. Mechanical grip now dominates in slow speed sections.
Recall from primer 3 that the downforce a wing produces is proportional to the SQUARE of the velocity of air moving over it. So, if the speed of the car is cut in HALF (like the reduction in speed from a superspeedway to a road course), the downforce produced by the wings is one FOURTH as much. This is why wing angles (and their physical sizes) are so much larger on a road course setup than on a superspeedway setup.
Also, although the driver is certainly an important part of going fast on an oval, I do believe that he/she is even more important on a road/street course. It seems that, although a proper setup is needed, the driver's ability is by far the most important variable here. Don't overestimate the ability of a setup to create a fast lap time on a road/street course. Don't underestimate the driver. Make sure you are either using the brake pedal or the throttle pedal - never coast. Also, be careful to have your front wheels straight before applying full throttle - the torque and power from the rear wheels will spin you out!
As in the case of an oval setup, we will always start with a well known road/street course fixed setup as our baseline. Our attempt will be to make it better or more suited to a driver's personal preference. All of the important variables will be addressed already for us if we choose a proper fixed setup. Then, based on particular track characteristics - bumpier, smoother, hillier, flatter, longer straights, shorter straights, etc. - we can use the following principles to "tweak" it just a bit.
IndyCar mandates the use of the road/street/short oval aerodynamic package for all road and street courses. Within this package, however, there are options. For example:
diffuser sidewalls/strake: optional (but suggested)
rear wing angle: 10.0 degrees to 46.0 degrees
In road/street setups, the 3 most important variables are grip, grip and grip!! Since aero grip is less important, we will spend our time understanding mechanical grip better. But first, a quick word about aero grip. Typically, we will want to add as much aero downforce as possible. Reason? Because of the reduced speeds, aero downforce is greatly reduced. You will want to compensate for this lack by adding as much as downforce as possible (without causing too much drag on longer straights). The only exception to this "rule" is if the road/street circuit has longer than normal straights (like the Indy road course or Road America). Also, since aerodynamic downforce really only becomes useful at speeds of 60 mph and higher, the other exception to this "rule" is if the road/street circuit has an abundance of slow corners (like Long Beach street circuit). In those cases, less than full aero downforce might be an option. Some trimming of the aero is possible, but generally the more grip produced by aero downforce the better. All of the items discussed in the previous primers are still in play. You will want to review all of the downforce tools from before - underwing and tunnels (and ride height), diffuser sidewalls and strakes, wickers (beam and wing) and upper wing angles. Also, as you analyze the downforce amounts, remember to use the "front downforce %" and "downforce/drag ratio" numbers in the "tires/aero" section of the GARAGE. After you have found a proper balance between front and rear aero, be sure to keep the "front downforce %" the same from before/after the change. If the balance is at 42% and you like that balance, make sure you keep that percentage the same as you make new changes to aero options.
Mechanical grip can be controlled by tire pressure, wheel camber, brake bias, ride height, springs, anti-roll bars and gearing (and some other, less important ways). Please see the document titled “Mechanical Grip in Corners” for a detailed discussion on these topics. A basic understanding is found below.
Work with the following:
1. tire pressure - they are much less than for an oval setup. Since lower pressures result in a softer, grippier contact patch and since tire temperatures are higher on road/street circuits (because of friction in the many turns), pressures can be up to 20 pounds less per tire. Also, they are usually symmetrical. In the case of rear wheel spin (whether from too much throttle input or oversteer), lower tire pressures in the rear tires may help their grip.
2. wheel camber - camber is a measure of how much the top of the tire is tipped in (toward/negative) or out (away/positive) from the center of the car. On an oval, the left front tire has positive camber and the right front tire has negative camber. As the car turns into a left hand corner, the car rolls toward the outside of the turn. This camber allows the inner and outer edge of the tires to contact the track equally. On a road/street course, all wheels have negative camber, to allow the outside tire's contact patch with the track's surface in a corner to be maximized.
The amount of negative camber can be analyzed by inspecting tire temperatures. After a practice run, you can determine whether the camber is correct by looking at the inner, middle and outer tire temperatures. The inner and middle temps should be within 3 degrees of each other and the outer will always be cooler. Since the outer edge of the tire is not in direct contact with the track on straights (or an opposite turn), expect the outer edge of tire temperatures to be less.
Also, since the front tires are being loaded in a corner more than the rear tires, the negative camber in the front will be more than the rear.
3. brake bias - a measure of how much braking pressure is applied to the front versus rear brakes. A number greater than 50% means more force is applied to the front than rear. If the car's rear end steps out on braking, the bias may be too far toward the rear brakes. Keep in mind, though, that a bias will create oversteer/understeer entering a corner. If the bias is at 58%, then the front wheels will brake with more force than the rears, may lock up first and not turn into the corner causing understeer.
4. ride height - a positive rake (the rear ride height is higher than the front) can create more downforce and grip, as it indirectly increases the upper wings' angles of attack. No more than a 1 inch difference between the front and rear ride heights is usually an appropriate value.
Any change you make to the car, whether it is tire pressure or spring stiffness (see discussion next) or even aero downforce will change ride height. Make sure the ride heights are the same - before AND after - any change you make to the car.
5. springs and dampers - on an oval, the springs need to be stiffer than on a road/street circuit. The forces and loads on the suspensions at 225 mph are so much higher than at 120 mph (or less). So, the springs will be set to levels much softer than on an oval. Also, slower corner tracks (or bumpy ones) will require softer springs than a track with faster corners (or smoother surface). You do not want to be in a car with stiff springs on a bumpy highway any more than on a race track. Stiffer springs work better on a smooth course with faster corners. Softer springs work better on a bumpy course with slower corners. Also, stiffer springs will create a faster steering response, softer springs will create a slower, more sluggish steering response. Keep in mind that a change in spring strength will create a change in ride heights.
Stiffer springs create more attitude control and less roll in a corner. Softer springs create more mechanical grip. Typically, springs are set to a higher (stiffer) value in the front wheels (for better roll control) and a lower (softer) value in the rear wheels (better grip and traction for the powered wheels).
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 more rear grip. Additionally, a softer front spring can decrease an understeer condition in a corner.
A disadvantage of using softer main springs is the possibility of the car "bottoming out" from acceleration, braking and/or aerodynamic downforce on a road/street course - especially at the beginning and end of a long straightaway. The 3rd spring can be used in conjunction with softer main springs to keep the car from scraping the bottom. The 3rd spring gap is used to control how far the main springs compress before the 3rd spring is activated.
Dampers can reduce compression (bump)/expansion (rebound) forces in the 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 springs oscillations and unwanted motions.
In the iRacing garage, in 'Dampers' section, you will see the 16 total damper settings listed. Very confusing negative 'click' numbers are used to show the amount and speed of the dampers. Rather than attempt to figure out the negative values and what they mean, use this rule of thumb:
use the right arrows to INCREASE (more) damping - i.e., stiffer
use the left arrows to DECREASE (less) damping - i.e., softer
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) dampers are 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 dampers would need to be decreased and reset to values that are slower than -15 clicks - perhaps to -17 or -18 clicks. Also, suppose the rear springs need to be softer, say 800 lbs. Then, the corresponding dampers would need to be increased and reset to values that are faster than -7 clicks - perhaps to -4 or -5 clicks.
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.
The documents titled "Mechanical Grip in Corners", "Mechanical Balance in an IndyCar", and "Major Suspension Units on an IndyCar" contain a much more detailed description of main springs, the 3rd spring and dampers.
6. anti-roll bars (ARBs) - indirectly, ARBs can help with mechanical grip. Although they are much less effective on an oval, ARBs on a road course serve a very important purpose - namely, they help balance the right amount of horizontal chassis roll. A softer front ARB creates more front tire grip, at the expense of less steering response. A softer rear ARB creates more rear tire grip, at the expense of more understeer and less rotation through the corner. Finding the right balance between soft/stiff front and rear ARBs can significantly affect how the car responds through a corner. A softer front ARB and a stiffer rear ARB can be used to help rotate the car through a corner - creating more grip on the front tires compared to the rear tires.
7. gearing - first gear can be a problem when maintaining grip out of a corner. As you apply throttle, especially out of a very slow corner, there is so much torque from the IndyCar turbocharged engine that rear wheel spin can be an issue. Making the first gear a bit taller or exiting the corner in second gear may help with wheel spin/grip. Also, 6th gear may be used on long straights. Make sure it is tall/short enough to give maximum power for the end of a long straight.
Finally, there are in-car adjustments you can make during a practice or race. The weight jacker is NOT an option to control oversteer/understeer. It is disabled in road/street configuration. However, the anti-roll bars are available and can help with control issues. Review the previous primers if you need to, but use anti-roll bars with understeer/oversteer issues in corners. Remember 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. You will need a total of 4 open buttons to program the front/rear ARBs as a unit.
Also, there is a push-to-pass feature invoked for road/street circuits. You can assign a button on the steering wheel (use one of the weight jacker buttons you are not using!!) to the push-to-pass. Each push of the button will provide an extra 50 horsepower (or so) for about 25 seconds. Most road/street races allow 10 pushes per race.
The push-to-pass button can be programmed in the "OPTIONS" section of iRacing, under "CONTROLS".
NOTE: THE RIGHTMOST NUMBER ON THE ROAD COURSE STEERING WHEEL DISPLAY INDICATES THE NUMBER OF REMAINING PUSH-TO-PASSES.
In addition to push-to-pass for power control, you can choose different fuel mapping positions during practice or a race. Found in the "drivetrain" option in the GARAGE, map "1" is full rich/maximum power, 2 through 5 are for green flag fuel saving, 6 and 7 are alternate throttle/power shapings (at full power), and map "8" is for maximum fuel saving under yellow flag conditions.
You will need 2 buttons on your steering wheel (or keyboard) dedicated to fuel mapping positions. Each button will be used to select a fuel map position (either up or down). They can be programmed in the "OPTIONS" section of iRacing, under "CONTROLS".
NOTE: THE MIDDLE DIGIT ON THE OVAL AND ROAD COURSE STEERING WHEELS DISPLAY INDICATES THE FUEL MAPPING SETTING.
The following fuel mapping information may help you decide which one to use:
fuel position 1 - max. rpm = 11,930 max. fuel rate = 43 grams/second
fuel position 2 - max. rpm = 11,789 max. fuel rate = 42 grams/second
fuel position 3 - max. rpm = 11,540 max. fuel rate = 41 grams/second
fuel position 4 - max. rpm = 11,305 max. fuel rate = 40 grams/second
fuel position 5 - max. rpm = 10,636 max. fuel rate = 40 grams/second
(above fuel positions 1-5 use a linear mapping algorithm: 10 % throttle = 10% power, 50% throttle = 50% power, 70% throttle = 70% power, etc.)
fuel position 6 - max. rpm = 11,929 max. fuel rate = 43 grams/second
fuel position 7 - max. rpm = 11,925 max. fuel rate = 43 grams/second
(above alternate fuel positions 6-7 use a progressive (non-linear) mapping algorithm: 10% throttle = 5% power, 50% throttle = 35% power, 70% throttle = 60% power, 90% throttle = 90% power, etc. This allows for less power output from the lower throttle inputs; more power output from the higher throttle inputs)
fuel position 8 - max. rpm = 10,914 max. fuel rate = 22 grams/second
From the above graph, it can be seen that fuel positions 1 - 5 use a linear throttle/power relationship - and a reduction in maximum power from positions 2 to 5. However, fuel positions 6 - 7 use a non-linear throttle/power relationship - and no reduction in maximum power.
This non-linear throttle/power curve for fuel positions 6 and 7 can be used to help control wheel spin out of a slow-speed corner onto a straightaway. Since wheel spin is a function of engine power (RPMs and torque), less power output with the lower throttle amounts can keep engine power below wheel spin thresholds. Also, notice that maximum throttle creates maximum power output - so, you are not losing any power, just redistributing it (less power with lower throttle input, more power output with higher throttle input).