Just curious... what tire pressures are you using? As stated, the sidewalls are pretty stiff to begin with, and overpressuring the tires only makes things worse, in that it diminishes the damping action of the tires and feeds more motion into the suspension - perhaps more than the shocks can compensate for. It's not a bad thing to run tires just a bit above the specs - as I do in my MG - but it has higher-profile tires. I drove my MINI from purchase last December until about a week ago, thinking that the rock-hard ride was normal - turns out all four tires were about 5 psi over, and while that might be okay on a track day, it can get pretty tiresome just driving around town.

Cheers,

Spridget

 

I'll check that out, Spridget; thanks for the advice.

 

From what I remember it was a small circular metal object that moutned somewhere toward the bottom of the steering rack.

 

it changes the tie rod angle relative to the lower control arm angle. For no bump steer, they should be parallel and the same length.

Matt

 

But the Mazda and the BMW's are bigger and heavier than the Mini

 

In my case what really helped with bump steer was the JCW slightly lower suspension and larger sway bars. It's still there but not as much. Switching to non RF tires didn't help much. I think the problem is the weight of the car and the stock height as well. With stock suspension it sits too high and jumps all over the freeway. Try it with 3 more passengers, it'll sit lower and there will be less bump steer.

 

IT'S NOT BUMP STEER!!!!!!!

Anyway, you all are complaining about the MINIs chassis dynamics, it has NOTHING to do with the angle of the tie rod to the control arm. What is really happening to almost all here is that the dynamics of the tire sidewall is poorly matched to the suspension tuning, and the suspension can't do it's job properly.

But I can see that I'm fighting a loosing battle. If it happens in a turn, it's pretty much universally called "bump steer" on the boards, no matter what the real source is.

Anyway, there is lots you can do about it. Mostly having to do with softer tire sidewalls and lower tire pressures to start.

Matt

 

OK. So what is bump steer? I just got that term from these boards, but if I'm wrong I wanna know!

So what are all of the options, aside from and including softer side walls and lower tire pressure? Why would BMW put such poorly mismatched tires on their cars?? I switched to non-run-flats but I guess they're still too stiff, in this case?

I actually had a very heavy load in my car last night (three really big people plus a heavy load in the back) and the problem was definitely reduced, so I'm inclined to agree with some of the other posters that it's partly a weight/height issue, too.

On a side note (I apologize in advance - ha!) it's "losing", not "loosing". I'm a spelling ****; I fully admit it.

 

Yes, as the song goes, it encourages you to "keep your eyes on the road, your hands upon the wheel...."

 

I'm not sure if you have an LSD. But what you're talking about almost feels like what happens to me when i hit a bump, but i know its due to the lsd.

 

"Bumpsteer", technically speaking, is what I described earlier. A change in toe angle as a result of bump (up) or droop (down) in the suspension.

What Dr. is saying is that ACTUAL "bumpsteer" isn't the main problem.

I imagine overall, that is correct. Think about what happen if you're driving a Go-Kart, which has NO suspension, and you hit a bump... the whole thing "bounces" away from the bump because there's nowhere else for that force to go.

To translate that to the MINI, here are two things to consider, IMO:

1. Suspension that doesn't smoothly damp bumps: If the suspension doesn't smoothly or sufficiently damp undulation such as bumps, you will get a go-cart-like bounce that feels similar to geometry-induced bumpsteer. Runflats would obviously magnify the problem relative to "regular" tires as they offer less secondary damping of movements.

2. Lack of suspension travel: I've heard that MINI's have but an inch or two of suspension travel before they hit the bumpstops, and also that most cornering actually happens ON the bumpstops. Anytime you're riding on the bumpstops or hit the bumpstops due to a bump, you're essentially in go-kart mode... virtually no suspension.


If the above two items are the problems, what can a MINI owner do? (non-exhaustive list)

- Switch to non-Runflats for more secondary damping
- Increase spring rate: This seems counter-intuitive for better ride quality, but if the problem is that you're hitting the bumpstops, then stiffer springs/swaybars will help to avoid that. It's sort of the "airbag" idea... airbags may hurt, but its better than hitting your face on the steering wheel (bumpstop). Of course, stiffer springs with incompetent shocks/struts do little good.
- Upgrade Shocks/Struts: Along the same lines as stiffer springs, dampers that are firmer yet offer more controlled damping can offer better ride (avoiding bumpstops, etc) AND handling.

 

I have that book too - very informative and it describes how to actually measure true bump steer (caused by toe change as the wheels move up and down). I have some TSW springs on order: I will measure the bump steer on the oem springs first and compare it to the lowered car. There are many reports of reduced torque steer on MINIs that have been lowered, but they might actually be refering to the bump steer.

FWIW I don't notice much bump steer while cornering, though the car does tend to skip over bumps. I think that is more an indication of lack of rebound damping in the shocks. I've got koni yellows on order along with the springs, - I'll let you know if they help in that regard once I get everything installed.