Quote:
Originally Posted by tsk94
Hi everyone. So I've been dealing with braking instability/movement under braking on a new track car build.
For some background, I tracked the car last year with the same brake setup back when the car was stock - upgraded pads, fluids and R compounds - and the brake stability seemed fine (wasn't pushing as hard as I am now though with the new build). I was running stock calipers, rebuild with brass guides, stainless steel lines, front backing plates with ducting and PFC 06 pads in the front (older version of the 08's). Initially was running 06's in the Front and 08's in the rear - this was causing the rear to lockup too easily, likely due to the large amount of weight transfer forward with the soft stock suspension. BimmerWorld recommended I use the PFC Z-Rated (PFC's street compound) in the rear, this solved the issue and the brakes worked great. No fade throughout the session and good balance on the otherwise stock car.
Fast forward to this year and the car has been fully converted to a race/track build. Fully gutted, 8 point roll cage, all suspension arms and bushing replaced with heim joints and solid bushings. Custom KW motorsports suspension, 800F and 1150R spring rates. Brakes were left unchanged however, as the setup mentioned above performed very well on the stock car I didn't feel the need to upgrades brakes immediately.
The first day test day with the new build I left the same brake setup as the previous season, PFC 06 in the front and the Z-Rated in the rear. No good anymore, with the much stiffer suspension the amount of weight transfer has been greatly reduced from stock, and the rear now doing more braking the Z-Rated wasn't a high enough torque pad. Also first noticed the instability under braking at this point, but I figured this was due to the brake balance being wrong due to the pads.
So, next track day I switched out the rears for some PFC 08's in the rear, technically should be the same, or very similar overall to the 06's I was running up front. Improved the braking in terms of stopping distances compared to before, but still had the wiggle/movement under hard threshold braking.
So what now? I've read of some people running higher torque pads in the rear to help issues like this, BimmerWorld and Turner have done/recommended this. So I picked up a set of PFC 11's for the rear - higher torque pad than the 06/08's. Ran this setup yesterday and the issue still seems to persist, the car just isn't that stable under hard braking, it's consistently moving around, not so much that you need to put in large steering correction, but enough to affect your confidence to attack the braking zones. The car will often pull to one direction or the other and movement around at the back end.
I don't believe this is an alignment issue, current alignment specs are:
Front: -3.3* camber, 0 toe
Rear: -2.5* camber, ~1/16 of toe IN per side, just above 1/8in total
1/4in negative rake - measured from the jack points
Running 275 NT01's all around for reference
I've read quite a bit of other members experiencing similar feelings with stock brakes on the track. It seems like the main solution is a BBK, some say just the fronts will solve it, others say you need F+R. Any other suggestions? Anyone have similar experiences?
|
Do you have video with data overlay that you're able to post? I am interested as to particular corners at particular tracks.