Ok, I have the coil-overs installed on my Cooper, and they work great. But, the car still has a fair amount of understeer. I have never owned a front-wheel drive vehicle and have managed to confuse myself on all this... (even though I am a mechanical engineer) Can someone post a quick summary on how to adjust a suspension to reduce understeer? I figure I need to change the dampening a bit in either the front or the rear, but it seems like it's different than a rear-wheel drive. Any info would be appreciated!

 

The least intrusive way to do it would be to increase the roll stiffness in the rear by increasing the diameter of the rear anti roll bar.
Alternately, increasing the stiffness of the rear dampers will do the same thing, but at a cost. The ride!

 

Softer in the front, stiffer in the rear.

A swaybar in the rear will make even a larger difference than the coilovers.

Feel free to contact me if you have any other questions.

Randy
720-841-1002
randy@mini-motorsport.com

 

I agree, stiffer in the rear.

However, since you have a coil over system, I would first try to stiffen the rear via spring preload and by adjusting the rear dampers to a stiffer setting. In my experience, it is much better to stiffen the rear via the springs and/or dampers than with a bigger sway bar. It is a myth that a stiffer sway bar will not degrade ride quality as much as stiffer springs. The sway bar is a spring and the only time that it is not as intrusive as stiffer springs is when both wheels go over a bump at the same time; how often is that in practice? At all other times when the wheels are going over bumps independently you will feel the stiffness of the swaybar. Worse is the fact that a swaybar connects the wheels while springs/dampers do not. This means that when one wheel goes over a bump, the swaybar will cause the opposite wheel to be affected; negating to some degree the benefits of an independent suspension.

I believe the rear wheels will have better traction, equal if not better ride, and reduce understeer by adjusting the rear springs/dampers rather than the swaybar.

I should say nothing is cast in concrete when it comes to suspension adjustment so in the end you have to experiment a bit. My main point is that since you've spent the bucks for a coilover setup, tune it first before going down the swaybar route.

I went with the rear swaybar because I only changed over to the H&R springs. If I had coilovers, I would have tuned them first.

Good luck and let us know what end up doing!

 

coilovers are a mixed bag; you get a lot of adjustment, but typically you won't be changing the spring rate (or the dampening/rebound) unless you get more sporty versions). Presumably, the coilover maker has optimzed the spring rate choice to match his damper.

You have to adjust the ride height carefully to get even corner weights, but this will only affect the difference in LH and RH cornering. There isn't any way to affect front-rear weighting with the spring settings.

 

Thanks for all the info! I think I will try to soften the front a little and stiffen the rear a little. Sounds like that will have the desired effect, to reduce understeer.

BTW, my shocks are Koni, fully adjustable...

 

Koni yellows? They are fully adjustable, but only for damping. They are a very nice shock. Go all the way stiff in the rear, then back it off three full turns. Go five turns from stiff in the front.

If they are yellows, and they are the same as the 914 models, that set-up (3 from full stiff rear and 5 from full stiff in the front) should work great for the MINI! (The set-up on the mid-engined 914 was totally different however)

Randy

 

shock dampening is a dynamic setting; it will affect the wheel movement only during a change in wheel postion by slowing down the change to a tunable degree. the final postion of the wheel will be determined by the springs and coupling of the sway bar in rreaction to the cornering forces. the dampening will affect the transiton into the corner; once the cornering attitude is set, it has much less effect.

the physicist in me wants to tell you the spring force is related to wheel displacement, the shock force is related to wheel velocity, but of course car tuning is a seat of the pants thing.

understeer/oversteer is a matter of relative traction, front and rear, affected by tire friction, which can be influenced by air pressure, corner weight, scrub angle and power delivery. For example, a common advice to correct for understeer in a FWD car is to let up on the throttle and steer to the outside of the turn a bit (reducing scrub) so the front tires gain traction again

 

O.K. Now, how will putting light weight wheels & tires effect the handling and ride? By going to the light weight wheels that Randy sells and using non run flats, (about 6 lbs lighter than run flats), could we get the same effect as changing springs, etc.?