Bumpsteer

[dmytro98]

After installing coilovers which lowered the car about an inch, but I never measured, along with adjustable upper trailing, camber and toe arms in the rear, I’m noticing a good amount of bump steer. I have got an alignment right after installing everything which led to about 2.5 negative camber in the front and 2.9 in the rear and basically 0 toe all around. I also have poly subframe bushings, and m3 control arms up front and I’m running 235 45 tires all around

[ShocknAwe]

Get another alignment.

Also recommend setting your height and F/R rake by ... Measuring.

[Biginboca]

Turner and SPL make tie rod ends that eliminate bump steer. With a 1” lowering I recommend you use the 1/4” spacer of what they include, this worked wonders for me with a similar lowering.

There seems to be a lot of ignorance about bump steer here and on the 3 series E9X forums, but it is real and with a 1” change in ride height you will experience it. The tie rod ends will eliminate it.

[dmytro98]

Is there anything that needs to be done to the rear to minimize bump steer?

[ShocknAwe]

What are you experiencing that you're calling bump steer?

Why or maybe better question is DID you specify or opt for -2.9 rear camber and zero toe?

Have you measured your ground to quarter panel clearance front and rear yet? Or ground to fender for that matter?

[dmytro98]

Any time I drive on a bumpy road the car darts all over the place. Also, the only reason I have so much camber in the rear is that without it the car rubs in the rear, and that's with my fenders rolled already. The 0 toe is to my knowledge it gives the car an aggressive turn in which is what I want, but I figure it could also be contributing to the bump steer. Also, I had the alignment shop set the ride height so I never measured the drop.

[tracer bullet]

You might not have what's normally termed as bump steer. You could of course, having changed some of the geometry, but FYI that might be the wrong term. You may have an alignment (i.e. toe) that you aren't used to or happy with. They aren't the same thing.

[ShocknAwe]

I like zero toe up front but it causes some tramlining.

You will want some degree of toe in for the rear. I like 1/8" total. Very stable.

If you recently set coilovers they may be too stiff with initial compression skipping you off bumps, or too much preload.

Too many variables but I'd really start with the alignment. If you're rubbing at least than -2.9 rear with a 235 width tire though your wheels really have poorly fitting offsets for our cars. The camber imbalance you have will just make you understeer more, negating the benefit of being square.

[tracer bullet]

Originally Posted by ShocknAwe

If you recently set coilovers they may be too stiff with initial compression skipping you off bumps, or too much preload.

Good point. Or so little rebound they've bottomed out without a chance to extend again.

[dmytro98]

I do realize that the camber offsets the benefits of the square tires, since the car still understeers at the limit and I was looking at adding additional camber to the front since I have good tire wear in the rear but the front definitely eats up the outside with the 2.5 degree of camber. If that doesn't get the car feeling more balanced I might just end up running 225 45 17 and reducing the rear camber since this car isn't built to compete but just meant to be fun canyon/track toy but I still want to have as much tire as possible. I'm running 17x8.5 et40 square which seemed to be a reasonable offset from the forums, but without cutting the inner lip from the rear quarter panels, the roll was not able to help very much with clearance. Not really sure what to do about the fitment since most people are able to fit 245/40 17 on the same spec wheels on a similar setup without rubbing. For the suspension, I have 70/120nm swift springs and ohlins r/t mi00 that were revalved for the springs. I'll try adding some toe in at the rear to see if that helps me out.

[ShocknAwe]

Ah you have Ohlins. What's your rebound set to and how many miles since install.

[dmytro98]

I have them set to 5 clicks from max stiff and somewhere around a 1000 miles since they were rebuilt. I bought them used and sent them straight to 3dm motorsport to be rebuilt and revalve.

[asbrr]

If they were revalved for those spring rates, for the street I would back off the shocks to the middle of the range (10 to 12 clicks from full stiffness). You need some suppleness to absorb bumps and let the suspension work.

That may be part of the issue, likely combined with geometry/alignment.

It's an easy adjustment, worth a shot. Remember to go full stiff on the knob before you back off to 10 or 12 from full stiff, that's the correct way to adjust the dampers.

[Bullitt]

Setting the rear toe to at least 1/8” each side should resolve much of the dartiness you are experiencing. If you have stock arms in the rear, bushing deflection will cause your rear to toe out if you run less rear toe. Zero rear toe is no good for this chassis even if you have upgraded arms and bushings.

17x8.5 +40 shouldn’t rub with a rear roll - it is likely your rear height is too low.

[dmytro98]

I don't have any pictures of the roll, but it is not a very aggressive roll, which is where I think a lot of my issues are coming from. Also, I have megan racing adjustable pillow ball camber, toe, and upper semi-trailing arm leaving only the semi trailing arm and spring arm with stock bushings.

[MightyMouseTech]

Less rebound and a bit of toe in on all four corners. Would probably go 2 minutes on each front wheel and 4 minutes on each rear wheel.

[Bullitt]

With those upgrades, you can have less rear toe, such as 4 minutes of toe-in as MMT said. I use to run as little as 2 1/2 minutes of rear toe, but I wouldn’t go less than that! It’s good to experiment as everyone has a different driving style.