I have been looking at coilovers for my 2006 MCS GP and I have a general question about spring rates. Many coilover setups have a higher spring rate in the rear than front, such as 7 kG (392 lb) in the front and 8 Kg (448 lb) in the rear, which seems backwards to me because the front has 60% of the vehicle weight. If I use some of the spring rate calculator programs I come up with something more like 7 Kg (392 lb) in the front but something more like 4.5 Kg (252 lb) for the rear for my Mini Cooper. Why do most coilover setups have such a high rear spring rate 450# verse the expected lower 250# when using 400# in the front? I have a couple theories but could be all wrong so I would like your inputs: 1. Just trying to stiffen the rear end to reduce understeer and assuming a stock size rear sway bar and no front camber plates. 2. If the car has a large adj rear bar, such as 22mm solid, and front camber plates (-2 deg or more) the rear spring rate could be closer to the 250# range.
The answer is number 1, but usually with a stiffer rear sway bar and camber plates. My spring rates are 400 on all corners (or will be I should say); but most are running 400 up front 450 rear to get to a slight oversteer for the track. I'd rather be closer to neutral, but it's really a personal preference thing, if you like sliding the rear out, then go with the higher spring rates on the back. If you're more point and shoot, go a little lower on the rear. Thing is, the rear end is very easy to catch on a MINI, so you can get away with a little oversteer. It all works together though--front and rear camber and toe, sway bar, tires, coilovers and springs, it all depends on your setup.
Thanks for the input. That makes sense. My car is a daily driver that I Auto-X but I want to lean to the softer side for street driving and compromise the Auto-X handling. I plan large bar and camber plates. Sounds like the 400#/400# range or even 350#/350# would make sense for me depending on coilovers.
Careful running too low of a spring rate. With a coilover you are reducing the amount of suspension travel you have available. Running too soft of spring will lead to bottoming out the damper.
I agree the MR is different front to rear. I believe the MR is about 0.99 (1) for the front and about 0.875 in the rear. I used those numbers in the spring rate calculators. I do not think I would go below 350 in the front, and I will only be dropping about 5/8-3/4". Do you think 350# is too soft?
350 still should be ok--it is for the KW V2's for example--but you always have make sure the spring rates are compatible with whatever coilover you choose.