travisnd

This weekend at RA I raced on 245 A6 scrubs. It was my first time ever trying to race on the setup (Ran TT on them in February and March at VIR). 10A at Road Atlanta is quite the test of braking. Per Traqmate data terminal speeds were 147-150 slowing down to around 55 in about 500 feet, all downhill. Car is a 2001 Z06 TTA/PTA racecar that weighs 3100lbs with me in it and 1/4 tank. Car was always raced starting full and had the cool-shirt setup full as additional weight.

I've always run Carbotech XP12s up front, but had 20s as back-ups after fading them during the RA race last December (or what I thought was fade, was racing on older 255 As). During qualifying on Saturday I felt I was fading the 12s again so I put in 20s for the race. They had more initial bite, but eventually I felt like they were fading again. It got to where I'd throw the anchor and time it so I knew the car would get slowed down, but I wasn't really in complete control if that makes any sense.

When I swapped out the 20s I checked everything. No air bubbles in the fluid, no degradation of the fluid at all, completely firm pedal, no pad taper, no signs of any issues to the calipers (Wilwood SL6Rs up front, stock rears). I have Titanium pad shims as well.

Another interesting fact is that I wasn't ever engaging ABS all weekend... anywhere on track. Then it clicked.... I think it's the small tires. As the 245s got hotter and hotter the car's braking ability went away. The tire controls how much braking force can be transmitted to the pavement right? So smaller tires that are really hot would have a hard time slowing the car down no matter how hard I push the brake pedal and how aggressive the compound right?

Greywolfe

I would think that if you had less grip from the smaller tires your ABS would kick in instead of feeling like brake fade.

AU N EGL

the rubber meets the road, for traction and braking.

What that balance point is the big secret. 305 front and 315 rear ?

sebdavid

That was my thinking too.

brkntrxn

Unless all four are sliding equally.....

SouthernSon

Stick some DTC 70's in there. Then you'll know if your ABS is working or not. I used to have to brake a little sooner with any carbotech compound. Not so with Hawk. You will be able to lock up tire at any time you wish.

travisnd

I hate Hawks. Ruined a good set of CCWs with some Blues years ago. Never again. Plus they're hell on rotors. Just my opinion

SouthernSon

True on every point. I used Carbos when running 1 pc. rotors. My 2pc. take the 70's much better.

SteveC68

I thought shorter tires had more of a negative impact on braking than narrower tires. So a taller tire should brake better than a shorter one.

ukrbmw

Chances of that can't be very high - braking force on the front would be higher than the rear.

I also would think you'd lock up smaller used A6s, especially with 20s in there. What about your booster? Do they leak on these cars?

travisnd

Posted another thread and had a long conversation w/ the folks at Carbotech. Consensus is I was seriously overheating the pads/rotors.

http://forums.corvetteforum.com/auto...otor-wear.html

Kubs

Brian, I have been following the other threads and agree that the main cause was the pad overheating. However, I think the narrower tire will actually improve your braking. Think of the contact patch of the tire. Your 255/275 width tire will have the same amount of contact, but the shape of the patch changes. The 255/275 contact patch will be wider side to side but narrower front to rear. The 245 tire will be narrower side to side but longer front to rear. Your braking and driving forces are in the front to rear direction (or longitudinal). The narrower tire has more grip in this direction that the others. Not to mention the 245/40 has more sidewall which will compress and flatten out the contact patch even more. I think you were working the brakes HARDER than you have before.