kelp

Before I head off to VIR Oct 20, I tested the GY slicks / Corsair wheels combo. Having the GT Brembo set I tested my decelleration. I do not have the TPS system in these wheels, and did not get any errors. However, my ABS kicked in really early, killing my braking force, yet there was no traction loss to activate them. Why? I will need the full use of these brakes at the track.

I wonder if it not having the wheels sensors telling the ABS the wheels are not turning activated the ABS prematurely. Anyone know how this works?

My solution: Although I have not heard of anyone doing this, I will pull the ABS fuse at the track. Thanks for your thoughts.

gkmccready

I don't think missing tire pressure sensor will have any effect on your ABS... the wheel speeds sensors are completely independent beasts. I'd look elsewhere to find your brake problems.

Haven't there been reports of Goodridge SS brake lines messing up ABS computers?

jlucas

Actually, it's the Goodridge ones that don't have that problem.

gkmccready

Oops. You're right. Ingle says it was Earls lines that gave him heartache.

AU N EGL

Yes from guys who never drive their cars. Not on the track

I am assuming these are the GY G19s. I have used these tires quite a bit on my C5. Some of the best braking I have had were with these tires. Stop so hard it felt like I was doing a motocycle stoppie. ( I know I know brake bias and shock rates )

Yes the ABS kicked in and glad it did, dont want to lock up those tires.

If ABS is kicking in early means your hard on the brakes too soon? Those big Brembo brakes have lots of clapping power. Far more then the stock Z6 brakes.

Remeber to learn the track first, then graduelly pick up speed and the braking zones.

MattW_VA

Did you have AH/TC off? My C6 will not stop from speed with slicks unless I have both off (never tried comp mode.) I do, however, believe that the ABS is a little to aggresive.

freefall

One question - what sizes are you running? I'm wondering if there's enough discrep between front and rear from stock to irritate the computer.

RAFTRACER

Maybe the "premature" ABS activation was caused by cold race tires.......Cold race tires are worse than cold street tires....... Or potentially were you accelerating with traction loss , before you tagged the brakes. Rear wheel spin to hard brakes= very poor braking and ABS "ice mode" or "sail-on" condition. Additionally,braking will be significantly different between high speeds and low or "normal" speeds. IE: the brakes on my autox car (03Z06) constantly drive me crazy with "ice-mode" during autocross, but never cause me an issue on a roadcourse.

kelp

Tires are GY Eagle GT1 G-19, R470 Front 25.5x11.5x18 (295), Rear 28.5x12.5x18 (320).

Yes, AH was off. My ABS definately turned on prematurely compared even with stock tires, and I have GT Brembos on other cars so I'm familiar with the feel they should have. Something is up.

It felt different than the normal rapid pulsing - just like the pedal got softer and there was less brake effect. Hadn't felt that before.

I pulled ABS fuse 27 and tomorrow morning I'll take it out and brake from 100 and compare.

AU N EGL

Get those tires heated up first. the GYs love heat.

kelp

The ABS fuse was a disaster. Everything locks up grossly. I wonder if cars brake more poorly now because of that assistance. Anyway I put it back in, steering assist was back, and strangely noticed it had more sensitive gas pedal also. Strange & interesting. So that's just the way it is.

My next question is one of traction -

Which is stickier the GY Eagle GT1 G-19 or Hoosier AS305 (treadwear 40)?

John Shiels

what compound GY?

J Ritt

The problem could be a less than optimum choice of piston sizing on the BBK you chose.

For starters, read this article. It will give you a good idea of how ABS works. http://www.stoptech.com/tech_info/wp...rakekits.shtml
The section that is titled "well lets see" (and the subsequent sections) is where you'll see your situation potentially being described.

I don't have the specs on the Brembo system on your car, so it's tough for me to verify mathematically if my hunch is correct. Are you running a four or six piston front caliper? Do you know the piston diameters and rotor diameter? What friction compound are you running when the abs issues occur?

What we see quite often on aftermarket systems, is that the piston sizing on the calipers is not ideal. In most cases, a larger rotor is added for more heat capacity, but the cailper piston bores tend to be too large. The result is a different pressure- brake torque relationship on a given axle than was intended from the factory. While the kit feels nice and grabby driving around town at first glance, the numbers tell a different story. Here's a good article on the importance of balance: http://www.stoptech.com/tech_info/wp...formance.shtml
The reason other manufacturers sometimes run into this is because they only have a certain range of caliper piston bores at their disposal. For example, if they have a six piston caliper available in six different piston bores, they'll choose the one that when mated to their chosen rotor diameter and pad choice will get them mathematically closest to the factory brake torque characteristics. With our systems, we do the manufacturing and set the bores at whatever our testing tells us they should be. We aren't working from a limited pool of piston sizes. Sometimes, the math doesn't jive perfectly with what track testing tells us. That's why our kits tend to play best with abs, etc.

I can't say this is definitely the case, but it is a possibility. Sub-optimal piston sizing (and most commonly overamplication of brake torque on the front axle) is often the primary culprit of early abs intervention.

If you get me the specs on the kit, I can see how they look vs. what we recommend for the car. At the very least the math will tell us if it's out in left field.

You definitely want ABS, and pulling the fuse shouldn't be the solution!