Nohachi's suspension ramblings thread

[NoHachi]

Spring stiffness: What works best stiff setups or softer ones.
Answer -> it depends

For starters..if you know your car, spring stiffness, suspension geometry, weights etc, you can calculate a "stiffness number" for your car (in actuallity it is the resonant frequency of an end of a car). This number is comparable between cars while springrates aren't even comparable between the front and rear of the same car.

Guidelines:
0.5 - 1.5 Hz for passenger cars
1.5 - 2.0 Hz for sedan racecars and moderate downforce formula cars
3.0 - 5.0+ Hz for high downforce racecars
from: http://www.optimumg.com/OptimumGWebSite/..._Tip_1.pdf

Examples in practice:

* 1990 Mazda Miata ~ 1.15hz front, 1.01hz rear
* Mitsubishi Evo VIII ~ 1.3hz front, 1.2hz rear
* Honda S2000 ~ 1.3hz front, 1.4hz rear
* GD Subaru WRX STI ~ 1.6hz front, 1.8hz rear
* Lotus Elise ~ 1.8hz front and rear
* C4 Corvette ~ 2.0hz front and rear
* Mazda RX-7 ~ 1.22hz front, 1.16hz rear
* Acura NSX ~ 1.6hz front, 1.5hz rear

AE86 values according to my model (disclaimer ->this model is NOT perfect, I'm just a hobbyist and make mistakes here and there. So maybe +/- 0.2 Hz):
Car - Spring rates F/R - susp.frequency F/R (description)
* Toyota AE86 1.8/2.2 ~ 1.3hz front, 1.5hz rear (stock)
* Toyota AE86 8/6 ~ 2.7hz front, 2.4hz rear (JDM-land)
* Toyota AE86 6/4 ~ 2.3hz front, 2.0hz rear (oldskull?)
* Toyota AE86 5.8/4.5 ~ 2.3hz front, 2.1hz rear (me and Ivan)
* Toyota AE86 3.5/3 ~ 1.8hz front, 1.7hz rear (best street setup?)

Possibly interesting setup values that I know off:
* 1990 Mazda Miata (1.6) ~ setup for stock class club racing on smooth tarmac tracks. Broke the class lap record during first training session.
2.28hz front, 2.09hz rear

*1993 Mazda Miata (1.9 turbo). Setup for Time Attack on Nurburgring Nordschleiffe (which is a very bumpy track, comparable to smooth streets).
Current best time 8min03 bridge to gantry. This years goal ~7.45 BTG and sub 8min full lap.
1.8Hz front, 1.8Hz rear

(note -> miata's, elises and other cars with double A-arms or other decent suspensions have good camber controll and can get away with softer springs)

If this interests you -> simple explanations here: http://buildafastercar.com/tech/Spring-Rates

[edit: some disclaimers have to be made:
(note -> miata's, elises and other cars with double A-arms or other decent suspensions have good camber controll and can get away with softer springs)
(note-> stock miata's are designed to corner on their bumpstops. New Mini's are similar in that respect. The bumpstops on a miata have increasing stiffness (up to 12kg/mm). Stock MX5 suspension frequencies therefor do not reflect their handling setup. They are far stiffer in handling then the freqs suggest.)
(note -> note that a stock AE86 seems backwards in regards to F/R springrate, this is compensated in roll (handling) by the swaybars (ARB's) ) This post has little to do with the "balance" of a car. It gets more complicated when you look at balance.