spring rates
Turbo Mini Forums

with the group buy im organising looking like it's going ahead I've just been thinking about spring rates for front and rear.

what spring rates would people think being a good starting point for a lightweight car aimed at track use?

will the added weight of me having my radiator in the boot affect the final spring rate that I need?


AW

Would it be better to run a stiffer spring or a softer spring?
I was thinking run stiffer spring if no one can confirm what springs to get, then adjust the dampers to be stiffer. Or will doing this just knacker the dampers?
Im going to run coilovers.

In boost we trust

One of the Allan Staniforth books (I've gone blonde and I'm having trouble remembering which one -- I think it's Competition Car Suspension) has a good section on selecting spring rates. It's a somewhat complicated process, you need to know what your motion ratios are (essentially the leverages your suspension arms) and you need to calculate your target frequency which will depend on what you'll be using the car for. Cushy street car is frequency of 0.6-0.7, track-day or rally use would be 0.8-1.2, track cars with downforce could be as much as 2.0-3.0.

There are formulas in the book for calculating spring rates from the other factors.

For the coil-over setup I'm using for my Rally Mini my starting point will be in the 325-350lb range in front, 125-150lb in rear.

I'm using a frequency in the 0.85 range.

t

Edited by andkilde on 24th Oct, 2009.

that's brilliant.

cheers for that.

Hey Andy

Having had a quick look at the Spax bracketry thread, you'll have to take the spring rates I quoted earlier with a grain of salt. If I use the Spax style lower mount I'll need significantly softer front springs. Spax lower mount places the lower shock pivot roughly at the ball joint, so you can ignore all my previous mumbo-jumbo regarding motion ratios, as they'll be 1:1 you can ignore them.

Gut feeling is I should be in the 225lb front, 125lb rear ballpark.

I'll run the numbers when I get a chance and report back.

t

theres some info in Alan Staniforth's race and rally car source book. ive got the book here but i cant get my scanner to work

i've got that book if you wan a lend Andy.