[Vetracr]

I have a 2010 BMW Z4 which has an E90 front suspension. I have upgraded the suspension with Turner monoball tension arms an M3 control arms. I also have Ground Control Camber plates, Koni FSD shocks with stock springs and have H&R sway bars and poly sway bar bushings. Bottom line is there is no deflection from rubber bushings in front suspension. I'm running 2.5 degrees negative camber and zero toe at the front. I'm having terrible problems with excessive feathering on the front tires when I run track days. The first thought I had was that BMW steering has excessive Ackerman built in causing a large amount of toe out on the inner right wheel during a right hand turn and vice versa on a left hand turn. The second thought was that I'm getting bump steer causing the tire to toe out during a turn. The M3 control arm is slightly longer than the stock control arm but setting the steering arm at zero toe should compensate for added length. Before I tear the front end apart to measure bump steer and ackerman has anyone run into this problem and if so how did you solve it? This is my first BMW and after fifty years of racing I've never run into this problem with a factory based suspension.

Pics of tire?

My first thought was that the FSD dampers might be doing a poor job of keeping the tires where they're supposed to be around not-so-smooth corners; particularly when the car is being driven @ 10/10...especially given how stiff the rest of the front suspension is.

[Vetracr]

Originally Posted by FCobra94

Pics of tire?

My first thought was that the FSD dampers might be doing a poor job of keeping the tires where they're supposed to be around not-so-smooth corners; particularly when the car is being driven @ 10/10...especially given how stiff the rest of the front suspension is.

Koni FSD shocks are matched to stock spring rates. They are stiff under slow compression like in a curve at the track and softer over hard high velocity bumps encountered on the street. I like them.

I've attached photos of tires showing feathering. Tires had just been run at Palm Beach Raceway which is hard on left side tires due to bias of high speed right turns.

[Vetracr]

I don't know how pictures got screwed up. Open images in new tab to get full view. first two pictures are of drivers side and second two are of passenger side.

[Volasko]

Aside from the feathering how did you like the F500's on the track?

[Vetracr]

Originally Posted by Volasko

Aside from the feathering how did you like the F500's on the track?

Firestone 500's are great comprimise tire for track days. Best combination of grip, wear and cost.