Warning you need to be good at maths.
Ok guys and girls. Here’s the formula to work out your spring rates for the car.
F= chosen frequency
MS= sprung mass (kgs)
MR= Suspension travel rate
K= Spring rate
K=4 x pi squared x F x square root MS x MR squared
Frequency = 2-6
Low downforce (superminis, city cars, hatchbacks, saloons, estates, trucks, vans,) = 2-3.5
Med downforce (Sports and super cars Ferrari, Lamborghini, lotus etc) = 3-4.5
High downforce (FIA/MSA race/touring cars/single seaters) = 4.5-6
Suspension travel rate
1.25, 1.35, 1.45 choose which rate fits the your style. The higher the rate the stiffer your springs.
Sprung mass
2506/4=626.5 (284kg)
(Total weight / 4 wheels= Sprung mass).
Chosen travel rate
1.45
Chosen frequency
2.5
Put it together
4 x PI squared x 2.5 x square root (284)x 1.45 squared =3496.99
Spring rate =349.69nm (after dividing 3496.99 by 10)
Add or subtract the difference in weight distribution
So for 43/57 it should look like this.
Front
349.69 - 7%=
Rear
349.96 +7%=
The result should be the perfect Spring rate for that car to deliver optimum weight transfer while minimising dive, maximising grip.
Example set ups
Soft set up (Ferrari 250 Berlinetta Lusso)
ARBs
12.16
9.41
Springs and ride height
249.6
239.5
8.1
7.9
Damping
6.5
6.8
6.8
6.3
Hard set up (Toyota Supra)
ARBs
26.52
18.16
Spring and ride height
572.9
713.4
6.0
5.8
Damping
8.3
7.9
5.6
4.9
See how with the softer set up I set the ARBs softer to allow the body to roll loading the tyres?? I’ve also got a higher bump stiffness to control the pitch and drive, allowing me to set the rebound lower to smooth the ride. So the damping is controlling the ride over all stability, ARBs are controlling tyre loading and springs are allowing more movement to give more grip using all 3 springs efficiently. You’ll need to run more camber at the front with a lower caster to rule out excessive camber while turning.
The hard Set up we see the opposite effect. I’ve got a much bigger ratio between bump and rebound. If you boost the rebound on stiff springs you’ll be skating over the track instead of griping to it, so we reduce the bump, increase the rebound to give a more complaint set up. What we also do it because we with this set up don’t want as much roll, we boost the ARBs considerably to provide a “flat ride” this will let you run with less camber putting more of the tyre on the track at any time generating extra grip. To compensate for the reduced camber however we need to boost the caster angle to aid turn in and exit grip.
The stiffer set up creates a less compliant car that is also much less predictable. Just as fast in the right hands but much harder to score consistently quick laps with.
Fixed.
