truffle shuffle under hard braking

[Sebringjetta]

Originally Posted by Billj747

I'm not sure i'd agree. Are you saying a F&R BBK would have a better (more forward bias) to fix the rear end wagging under braking?

When you had the issue and it was solved by the F&R BBK, did you use the same pads F&R pre and post BBK?

I still think the OPs issue is too aggressive of a rear pad for the stock brakes. Since he's going BBK, if he runs a less aggressive rear pad and/or if the caliper piston sizes are balanced and he runs the same pads F&R, I think his issue will go away.

well im on the track next week and will be placing my bbk on this week so we will see what happens....ill keep the tire pressure the same as well and if i get the same results ill try lowering the the psi and see if that changes....then if it keeps up ill take a look at the toe... but none the less appreciate all the help fellas!!!!!

[bigjae1976]

Originally Posted by SenorFunkyPants

It will be interesting to see what you get.
It would be an undesirable characteristic if the rear wheels did indeed toe out during braking...as that would make the rear less stable.

With 0.10' toe in on each rear wheel (total 0.20') you are nearly at the maximum of the stock total rear toe spec of 0.22' toe in.
I have 0.04' on each side of my (road car use only) M3 and that works really well for spirited driving even on very bumpy country roads.
Maybe might be worth trying something similar? Might help the car turn in a bit easier?

The E46 toes out under acceleration which I think would be even less desirable?

I haven't experimented a whole lot in the rear with toe. Might give it a try.

Originally Posted by Billj747

I'm not sure i'd agree. Are you saying a F&R BBK would have a better (more forward bias) to fix the rear end wagging under braking?

When you had the issue and it was solved by the F&R BBK, did you use the same pads F&R pre and post BBK?

I still think the OPs issue is too aggressive of a rear pad for the stock brakes. Since he's going BBK, if he runs a less aggressive rear pad and/or if the caliper piston sizes are balanced and he runs the same pads F&R, I think his issue will go away.

I'm not sure I'd 100% agree with me either. I had Pagid Yellows on both axles with the BBK and then PF01s with the OEM brakes. As far as bias, I am not sure that it changed much with the BBK.

I guess I didn't get into the details of my theory. The STs allow much smoother modulation and, for me, application of the brakes. Part of it is the elimination of the "I'm going to die" reaction with the OEM brakes so you nail the brakes and the other part is the better and more responsive stopping power. So with the BBK, the car was balanced better under threshold braking. On the OEM brakes, I certainly created more weight transfer, taking a lot of weight off of the rear causing the rear to get light.

I would also think if you had too much rear bias and caused the rear tires to lock up that ABS would intervene.

[SenorFunkyPants]

Originally Posted by bigjae1976

The E46 toes out under acceleration which I think would be even less desirable?

Its been a good many years since I did extensive suspension work (and that was on a 911) and now refreshing my knowledge with a bit of reading up on the subject showed me just how much I had forgotten or mis-remembered.
So you most likely are far better informed on the subject than me.
I do think though that a bit of experimenting with the rear toe might be interesting - if nothing else reducing the toe will extend your tyre life.

[kaleb]

I just wanted to chime in that I experienced this "truffle shuffle" at COTA this weekend at the end of the 130+MPH straight braking for turn 12. I ran Pilot Super Sports, PFC 08 brakes on FRONT only, and stock EDC suspension. My PSI was set at 32 cold, which would get me to about 38-39 hot.

[bigjae1976]

Originally Posted by kaleb

I just wanted to chime in that I experienced this "truffle shuffle" at COTA this weekend at the end of the 130+MPH straight braking for turn 12. I ran Pilot Super Sports, PFC 08 brakes on FRONT only, and stock EDC suspension. My PSI was set at 32 cold, which would get me to about 38-39 hot.

Lol...I wasn't even scared.

[Sebringjetta]

by the way fellas installed the bbk...lowered the psi and no longer a truffle shuffle!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!