Suspension_Spreadsheet
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Suspension Tuning Calculations
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By Rob Robinette V10.0
Download latest version of this spreadsheet:
Suspension.odsSuspension.xls
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Enter values in blue, numbers in black are calculated. All Weights in lbs (NC Miata in parenthesis)
AutoMath.xls
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2480
Car Weight (2480 lbs for NC Miata)
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175
Driver Weight (175 average)
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50.4
Fuel Weight (100% Rear)
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Gallons US Fuel
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2705.4
Total Car Weight
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52.0%
Front Weight Distribution (52%)
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48.0%
Rear Weight Distribution
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1,381.6Front Weight
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1,323.8Rear Weight
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58.7
Front Track (58.7in for NC Miata)
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58.9
Rear Track (58.9in)
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Calculate Unsprung Weights
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Enter weights for one corner in lbs (NC Miata)
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Front Wheel (17)
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21Front Tire (21)
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25
Front Knuckle (25)
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7
Front Lower Arm 40% (7)
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20
Front Shock & Spring (20)
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14.3
Front Brake Rotor (14.3)
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8.3
Front Wet Brake Caliper (8.3)
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225.2
Total Front Unsprung Weight ( * 2)
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578.2
Front Sprung Weight Per Wheel
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30
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Rear Wheel (17)
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21Rear Tire (21)
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Rear Knuckle (23)
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14
Half Shaft 50% (14)
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4
Rear Lower Arms 50% (4)
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20
Rear Shock & Spring (20)
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9.3
Rear Brake Rotor (9.3)
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6.75
Rear Wet Brake Caliper (6.75)
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230.1
Total Rear Unsprung Weight ( * 2)
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546.8
Rear Sprung Weight Per Wheel
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455.3
Total Unsprung Weight (455 for NC Miata)
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2250.1
Total Sprung Weight = Total Car Weight – Total Unsprung Weight (2250)
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Front Suspension
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0.78
Motion Ratio (spring to wheel motion, 0.78 for NC Miata)
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15
º Angle Between Spring and Lower Control Arm (degrees, 15 for NC Miata)
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0.9659258263
Spring Angle Correction Factor = Cosine(Spring Anglel)
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165
Spring Rate (lbs-in or N-mm, 165lbs for NC Miata)
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97.0
Wheel Rate (lbs-in or N-mm) = Motion Ratio^2 * Spring Rate * Spring Angle Correction Factor
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76.91
cpm Suspension Frequency (cycles per minute) = 187.8 * SquareRoot(Wheel Rate / Sprung Weight)
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1.282
Hz Suspension Frequency (cycles per second) = Suspension Frequency / 60 (1.28 for NC Miata)
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54
Rear Suspension
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1
Motion Ratio (spring to wheel motion, 1.0 for NC Miata)
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15
º Angle Between Spring and Lower Control Arm (15 for NC Miata)
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0.9659258263
Spring Angle Correction Factor = Cosine(Spring Angle)
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158
lb-in Spring Rate (158)
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152.6
lb-in Wheel Rate = Motion Ratio^2 * Spring Rate * Spring Angle Correction Factor
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99.21
cpm Suspension Frequency (cycles per minute) = 187.8 * SquareRoot(Wheel Rate / Sprung Weight)
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1.654
Hz Suspension Frequency (cycles per second) = Suspension Frequency / 60 (1.432 for NC Miata)
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1.290
Front to Rear Suspension Frequency Ratio (1.12 for NC Miata)
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Roll Stiffness & Roll Couple
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200
lb-in Front bump stop rate* (200 for NC Miata)
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121.7
lb-in Front Bump Stop Wheel Rate (156)
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374
lb-in Front Sway Bar Rate (374)
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136.4
lb-in Front Sway Bar Wheel Rate (137)
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379.4
lb-ft-degrees Front Roll Stiffness = (12 * Pi * (Track Width in feet)^2 * Wheel Rate) / (180 * 2) + Sway Bar
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501.1
lb-ft-degrees Front Roll Stiffness + BumpStops = (12 * Pi * (Track Width in feet)^2 * Wheel Rate) / (180 * 2) + Sway Bar + BumpStop
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NC Miata 469 & 625 + Bump Stops
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100
lb-in Rear bump stop rate* (100)
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100.0
lb-in Rear Bump Stop Wheel Rate (87)
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106
lb-in Rear Sway Bar Rate (106)
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54.0
lb-in Rear Sway Bar Wheel Rate (54)
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439.0
lb-ft-degrees Rear Roll Stiffness = (12 * Pi * (Track Width in feet)^2 * Wheel Rate) / (180 * 2) + Sway Bar
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539.0
lb-ft-degrees Rear Roll Stiffness + BumpStops = (12 * Pi * (Track Width in feet)^2 * Wheel Rate) / (180 * 2) + Sway Bar + BumpStop
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NC Miata 345 & 432 + Bump Stops
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818.4
lb-ft-degrees Total Roll Stiffness = Front Roll Stiffness + Rear Roll Stiffness
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1040.1
lb-ft-degrees Total Roll Stiffness With Bump Stops = Front Roll Stiffness + Rear Roll Stiffness
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NC Miata 814 & 1057 + Bump Stops
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46.36%
Front Roll Couple* = Front Roll Stiffness / (Front Roll Stiffness + Rear Roll Stiffness)
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48.18%
Front Roll Couple* With Bump Stops = Front Roll Stiffness / (Front Roll Stiffness + Rear Roll Stiffness)
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*Bump stop stiffness only comes into play when the main springs are fully compressed at max suspension travel.
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NC Miata 57.6 & 59.11 + Bump Stops
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This table uses above values for sway bar rates, motion ratio, spring angle, sprung weight and track width
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Fr SpringsRr SpringsFr Wheel RtRr Wheel RtFr FrequencyRr FrequencyFr Roll StiffRr Roll StiffFRC
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16515897.0152.61.2821.654617.0491.055.68%NC Miata
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300196176.3189.31.7281.842815.8583.658.29%FM Stage II
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325275191.0265.61.7992.181852.6776.252.35%
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400336235.1324.61.9962.411963.0924.851.01%
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560336329.1324.62.3612.4111198.6924.856.45%
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500400293.8386.42.2312.6311110.31080.850.67%
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500500293.8483.02.2312.9411110.31324.545.60%
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600400352.6386.42.4442.6311257.51080.853.78%
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600500352.6483.02.4442.9411257.51324.548.70%
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600600352.6579.62.4443.2221257.51568.144.50%
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700400411.4386.42.6402.6311404.81080.856.52%
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