Weird brake bias issue

[Tut4u2]

I have been trying to hunt down a brake bias issue with my car. Under heavy braking on track (anything about 90MPH), the rear of the car gets light and starts to wander around a bit. I have tried running different pads (SR33, Stoptech Sports pads, as well as Hawk DT70) non-staggered and the issue still persists.

From an alignment perspective, I'm running -3/-2 camber F/R, with 1/8in toe in total front, and 1/4in toe in total rear, as well as -3/-1.5 camber F/R with 0 toe front and 1/8in total toe in rear.

All my bushings are true all around, everything is torqued to spec, and nothing in bent.

Any tips on what else to try? Thinking about putting a more aggressive pad in the rear but that would be a first for me.

[roastbeef]

are you running monoball front control arm bushings? oem bushings can squirm under hard braking. just a thought.

i don't know how much seat time you have, but it sounds like you have enough where its not a technique problem.

are you running the same compounds front and rear?

[Tut4u2]

Same compound front and rear. I replaced the front arms with Trw replacement thinking there was some deflection upfront as well but no improvements.

Oh, I'm running ST60/ST40 calipers. The wear on the pads is consistent between driver and passenger side so I dont think it's a caliper issue either.

I'm not Lewis Hamilton, so could always be a technique issue hah. I don't experience this in my other track cars though.

[Redd]

I have Brembo GT with Pmu HC+ pads front and rear. Rear end squirms under hard braking, it's normal. Front monoballs help some.

[tdott]

The weight is going to shift to the front and make the rear light under heavy braking.

Can't really say if yours is more than normal or not, but it doesn't sound like there is anything inherently wrong unless it's really extreme.

What suspension are you running? Perhaps you have too much rake? Try lowering the rear, or raising the front. Corner balancing may help also.

[SAMM3Y]

Rear inner lines switched too? Running any aero?

Maybe just use it to your advantage when trail braking... "loose is fast"

[Dreamer99]

I have ST60/ST40 brakes with Cobalt XR3 pads front and rear and get the same squirelyness under heavy braking as well. Thought it might be the tires getting greasy from heat.

[Tut4u2]

Originally Posted by tdott

What suspension are you running? Perhaps you have too much rake? Try lowering the rear, or raising the front. Corner balancing may help also.

Running Bilstein B6 with Eibachs springs and GC Top Hats.

Originally Posted by SAMM3Y

Rear inner lines switched too? Running any aero?

SS Brakes lines all around and using SRF fluid. No aero.

Originally Posted by Dreamer99

I have ST60/ST40 brakes with Cobalt XR3 pads front and rear and get the same squirelyness under heavy braking as well. Thought it might be the tires getting greasy from heat.

I was thinking it might be tires as well, but I'm run these until the end of this track season.

[Tut4u2]

So yesterday I experienced the same issue on track. This morning I swapped in different rotors and flushed out my brake fluid again and the problem looks to have resolved. Granted conditions are different on street, so I will report back after my next track day.

[Redd]

Many cars that I've driven with big brakes do this, even factory installed ones. Its not something to worry about unless your tail is actually stepping out in a dangerous manner.

[VictorH]

[QUOTE=Tut4u2;26608971

Any tips on what else to try? Thinking about putting a more aggressive pad in the rear but that would be a first for me.[/QUOTE]

Your alignment seems fine. My car used to do exactly the same thing and the faster you were going the more unstable it felt. It was 80% fixed with what you have in your last line. A more aggressive rear pad with more bite will even things out and make the rear more stable.

One thing to note, particularly if you get into ABS, and you have any steering input at all, i.e. the wheel is not completely straight, almost all modern street cars will dump all the rear brake pressure (I've seen the pressure curves), at that point the rear is just along for the ride. Give a more aggressive rear pad (more than the front) a try, I think you will find it helps quite a bit.

[roastbeef]

Originally Posted by Tut4u2

Same compound front and rear. I replaced the front arms with Trw replacement thinking there was some deflection upfront as well but no improvements.

Oh, I'm running ST60/ST40 calipers. The wear on the pads is consistent between driver and passenger side so I dont think it's a caliper issue either.

I'm not Lewis Hamilton, so could always be a technique issue hah. I don't experience this in my other track cars though.

i don't think there is much more you can do. under heavy braking, its going to feel like the rear wants to come around a little bit if your steering wheel is even slightly turned. even having monoballs, running complimentary pads on a front and rear bbk, and careful braking- it still happens. i'm an ameature at best but i think it just happens. i try to influence the "squirm" to my advantage with my steering input and call it the beginning of trail braking. i was thinking maybe you did have a bias, but i'm now thinking what you're describing is what we all just have to work with.

[Dreamer99]

I did lower the Ohlins coils on the front of my car 1/4" from the manufacturers set height. I wonder if the additional rake makes a difference.

[Bartledoo]

Sounds like the car wants to help you turn! My car was like this pre-aero. It was fun and made corner entry more lively.