I have one final issue I need to tune out of my car before it will be what I consider as perfect. The problem I am having is rear end squirm when braking hard from 110mph in a straight line. I don't have this problem unless I am over 100mph.

It feels like the rear is not tracking straight when braking hard. I end up having to make steering input adjustments.

I have fairly stiff suspension, corner weighted, mild alignment, street tires, and I'm running XP12 fronts XP10 rears. Could it be the mismatch in pads? I am running the 12s up front because they see alot more heat than the rears do.

I did some searching and found this thread:
https://www.evolutionm.net/forums/sh...d.php?t=144789

Not much info there. I've also read that it could be trailing arm bushings. I haven't really found any solid suggestions. Help.

Jeff Jeske

Do u have any rear toe out?

What tires? Could be sidewall squirm under braking. How much front camber? One of the downsides of a lot of front camber is that the back end will move around under hard braking.

Toe out would definitely do it. Also, if you're on a bumpy surface and you have a very stiff set-up at the rear, that could unsettle the rear end under hard braking. Basically, all the tricks you use to help an AWD/FWD rotate will also make the rear end skittish under braking.

Emre

FWIW - I'm using different pads front/back and my car tracks dead straight during hard braking. My rear pads are still stock, so I'm figuring the front is grabbing a lot harder and doing a majority of the stopping.

My toe is pretty much zero'd out in the car.

I had the same issue during high speed braking. The rear always wanted to dance around. I never identified the problem, but I noticed it went away after the tires warmed up. It was worse if the tires had not been used in a while.

As mention already, it could be that your tires are not warmed up enough and you are simply losing traction. I had that problem when I first used my Nitto's. The problem went away as soon as I get more heat into them.

EDIT: I forgot to mention that I have rear trailer arm bushings and a set of Ohlins (650lb front and 750lb rear spring rates). I would still run into the same problem you were describing, until I figured out that I needed more heat in the tires.

I had it at every track event when on the stock suspension due to my rear end lifting up in the air and having less contact with the ground, but as soon as I got my Ohlins, it stopped completely. My braking has become seamless whereas before it was a chore.

I run -2F / -1R with 0 toe. I am using a new set of stock advans.

It was a lapping day with 20 minute sessions so its hard to remember if I fought the issue the entire time or only with cold tires. Its something to keep in mind. I have another lapping day May 4th where I'll be able to test and tune a little more.

I don't believe the problem is due to dive. The car is fairly flat even under hard braking or high g's. I suspected dive the was cause on the stock suspension and was hoping the coilovers would solve the problem.

I suppose I could have the alignment checked again but the car tracks perfectly in all situations other than +100mph heavy braking.

How many of you run mismatched pads front and rear?

Just a stab in the dark here, but what about uneven brake bias in the rear?
Pads not making a flush contact with the rotor?
My .2c worth.

What is your rear ride height set to? How about rear compression/rebound compared to the front? Are you still using the stock roll bars?

d

I lowered the car about 3/4" rear and 1" front. The car has a Perrin rear sway bar. No strut tower bar although I was considering one. Here is a ride hieght pic for reference.....

I run the same pad combination and my rear sways also. I have completely stock suspension, -1.98 F -2 R, 0 Toe, Goodyear GS-CS and Hoosier R6 tires.

For the rear? The rear suspension doesn't use struts. A bar attached to the shocks doesn't do ANYTHING.

EDIT: as far as ride hieght goes, that doesn't look too bad. When i first installed my coilovers i lowered the front ~1 inch but the rear only 1/4 inch. This caused HUGE instability during hard braking and high speed corner entry.

EDIT2: Maybe Paul G or JonK can chime in here, as they have more road course setup experience. I do know that the top autoX evos get the rear very low. My own testing has found this to be faster on road courses too, but most folks seem to put in rake.

EDIT3: Oh, one more very important thing. I have no wing. Even stock the rear was a little light over 100 mph.

d