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how do you increase stability under brakes?

domesticpower

Track Addict
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The car seems to jiggle/squirm under hard braking which is very unsettling. I hardly notice it over smooth sections of the track but it's bad over the rougher sections. Is it something I simply have to live with because of the LRA getting unsettled over bumps or it's something that can be improved? The brakes are stock. Tires are 285/35/18's Contis ExteremeContact DW all around mounted on 9.5's. Only other suspension mod is a Watt's link. Thanks in advance!
 
Shock and spring adjustments can help you out with this, but in general, from what I've found, you're going to get this if you are braking hard over rough/uneven surfaces to some extent in general, SRA or not. Actually, LCA's with some type of rod end can help the rear out in this too. Whatever you do to help with this will most likely affect something else along the way.
 
Stiffer springs will reduce the brake dive which unsettles the car. An inexpensive mod that also lowers the car/center of gravity and reduces body roll.
 
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I was battling this with my car as I was pushing hard and harder (back when I was learning the car still).
An increase in rear rebound helped this tremendously. Car is much more composed under braking (though under very hard braking, it'll still get antsy).

There's just tons of forward weight transfer going on, and the car is front heavy to begin with. The others nailed it: Stiffer springs will help (along with lower CG).
Rebound helps, and more anti squat out back can help. OH let's not forget anti dive up front -- which can be done with some aftermarket K members or KB arms.

IIRC whiteline made front LCA bushings for our car with some anti dive built in. That's also an option.
All anti dive is doing is changing the angle of the front LCA relative to the ground. Raking the LCA forwards will reduce front end compression under braking.
 

steveespo

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Alignment settings are a factor too, less camber up front and close to zero toe (either +1/16" or -1/16") will help braking and straightline stability. As always it's a compromise on where the most time will be found. Sometimes it will be better to back up the brake zones with less agressive braking to have maximumum turn in and cornering performance. Other times like a long straight to a hairpin to a long straight, you want to have best braking and acceleration traction to maximize time at speed on the long straights.
Steve
 
you may also want to consider reading Kenny Brown's comments on this topic....from what I could gather in talking to him about this is that as he continued to increase spring rates (and he tends to run extremely high spring rates) he began to find that the torsen diff, itself, was contributing to the problem. He specs wavetrac (I believe) diffs in his builds for this reason.

what others in the thread have mentioned is certainly true...that unloading the rear as much as these cars do with the stock spring setup will certainly cause all kinds of 'loose' feeling in the rear. When you say 'jiggle' it makes me think: really light rear end...but when you say 'squirm' it makes me think of a diff hunting for traction L-to-R.
 

Grant 302

basic and well known psychic
boro92 said:
I was battling this with my car as I was pushing hard and harder (back when I was learning the car still).
An increase in rear rebound helped this tremendously. Car is much more composed under braking (though under very hard braking, it'll still get antsy).

There's just tons of forward weight transfer going on, and the car is front heavy to begin with. The others nailed it: Stiffer springs will help (along with lower CG).
Rebound helps, and more anti squat out back can help. OH let's not forget anti dive up front -- which can be done with some aftermarket K members or KB arms.

IIRC whiteline made front LCA bushings for our car with some anti dive built in. That's also an option.
All anti dive is doing is changing the angle of the front LCA relative to the ground. Raking the LCA forwards will reduce front end compression under braking.

I think most of the easier solutions are listed here. Lowering and damping are probably the easiest places to start. Revised suspension parts and geometry in the rear is easier once lowered, but might be a good place to start if for some reason you want to keep the stock ride height. Anti dive changes up front might require other mods for steering adjustment.

If you are feeling any issues like pull or shudder through your steering wheel, then as Steve suggests, a proper alignment would help.
 

domesticpower

Track Addict
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Thanks for all the responses. No issues with the steering wheel and I've checked alignment a couple of times this summer and its all in check (stock).

I have been interested in the Vorshlag-Bilstein cc plate, spring and shock/strut package for a while so looks like there's even more reason to get it. I think it makes sense that its due to weight transfer to the front because where its most noticeable on the track is in a downhill corner so the back end is already slightly unloaded.
 
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I was just thinking about bump steer, are the steering arms parallel with the lower control arms? IF not, like the car is lowered and you have not compensated by adjusting the tie rods, that could be your problem.
 

domesticpower

Track Addict
190
134
NS
ArizonaGT said:
The manner and speed in which you apply braking can directly affect car composure via weight transfer. Get on the brakes too hard too fast, the rear of the car will wag around.

ah I see.

blacksheep-1 said:
I was just thinking about bump steer, are the steering arms parallel with the lower control arms? IF not, like the car is lowered and you have not compensated by adjusting the tie rods, that could be your problem.

no the car is not lowered. I think it is because I have to roll in the brakes too fast like ArizonaGT said combined with the braking zone being just past a crest where the car is unloaded. I hope upgraded springs/shocks will help and possibly with rear control arms.
 

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