Track guys, question on rear brake pads....

[YellowViperSRT10]

Hey Guys,

I been running my 08 coupe on the track A LOT lately, and been noticing my rear brakes are getting hotter then the fronts and the rear brake pads are also wearing down almost twice as fast as the front. Which is very usual as the fronts usually go quicker then the rears on most cars. I am using Porterfield R4 race pads on the track only which are excellent, I am curious to know how many others see their rear pads wearing faster then the fronts? I spoke to engineer who developed our brake rotors and he said the fronts can be cooling a lot better because of the very efficient factory bake cooling ducks. But the rear does not have any. We are going to take the car back to Homestead next weekend and then in April go to Homestead for 2 days with it, and check the front and rear temps. We will then also fab up our own rear brake cooling ducts, and if it keeps temps down, we will make it in a carbon fiber version for production. But I first wanted to know if some of you guys on the track see the rear pads wearing faster the fronts..

Thanks

 

[Chuck 98 RT/10]

Sounds very unusual. So much so that I would go over the system thoroughly.

 

[Bob Woodhouse]

Lets go slow on your conclusion. More info needed. Is your tire diameter exactly the same as what the car was delivered with? Not tire, but dia. This is critical to brake temp since if the leverage changes it may cuase your rear axle to be doing more work than intended. Do you have the same pad compound being used on both ends? Do you know if your ABS is working properly? Tire dia. will also mess with your ABS and your front to back electronic biasing. Keep in mind that 65 to 75% of the brake load is is designed to be done by the front due to weight shift when decelerating and the reason you have big rotors and pads in the front. Are you fading, heat checking, rotor cracking or any other hot symptoms on the rear brakes? Pad wear is a square root factor of temperature causing pad life to be short when they run hot. Air ducting is not likely to be the solution, that is putting a band aid on the sore, lets find what is making the sore. There is a possibility your car has more stopping power in it than you are getting at this time due to the imbalance front to back in the brakes.

 

[BennyBad]

did homestead yesterday and i had my ir gun with me checking rotor temps on a friends Z06 that keeps warping rotors. after a full 2 mile cool down lap and paking in the paddock the Z06 fronts were still at 550 rears at 250 while my acrs were at 150 front and 130 rear and a 08 coupe friends were 250 front and 180 rear pretty consistent all day. examined were on pads at lunck everything looked good and even. other frienf with 06 coupe last session came in with front pads smoking and rotor temps at 900 degrees, front pads were toasted, we believe do to the 20000 mile run craps that were finally failing. somehting doesnt sound right. i track my car twice amonth and dont have this issue.

thanks

 

[GR8_ASP]

Not sure about the wear but I have found using a higher friction front pad versus the rear provides better braking stability. This is with 18 all around (sport cups) so the front to rear ratio is out a bit. I use Brakeman 3 fronts and stock rears. Stock pads all around was ok but could not handle the brake temps. When I put Brakeman 3's all around it was too skittish under hard braking.

 

[cheryl mccally]

Lets go slow on your conclusion. More info needed. Is your tire diameter exactly the same as what the car was delivered with? Not tire, but dia. This is critical to brake temp since if the leverage changes it may cuase your rear axle to be doing more work than intended. Do you have the same pad compound being used on both ends? Do you know if your ABS is working properly? Tire dia. will also mess with your ABS and your front to back electronic biasing. Keep in mind that 65 to 75% of the brake load is is designed to be done by the front due to weight shift when decelerating and the reason you have big rotors and pads in the front. Are you fading, heat checking, rotor cracking or any other hot symptoms on the rear brakes? Pad wear is a square root factor of temperature causing pad life to be short when they run hot. Air ducting is not likely to be the solution, that is putting a band aid on the sore, lets find what is making the sore. There is a possibility your car has more stopping power in it than you are getting at this time due to the imbalance front to back in the brakes.

Listen to Bob Woodhouse when he speaks about this issue. A rear brake bias can cause all sorts of problems on the track. You need to find out what's going on.

 

[mjorgensen Woodhouse]

I thought Homestead was a brake killer of a course? When was the last time you bled the brakes including the ABS module? If you have over cooked the fronts and there is air in the calipers/lines then the efficiency of that end could be compromised and the rears are taking more abuse than they should be. Do you feel the ABS activating at all on course? When and during what maneuvers? The cooling in the rear is obviously less than the front and if there are hard brake zones and short straights the rears may just be running overall hotter that the fronts and thus over heating the pads.

Bleed the brakes fully the next time out and pay mind to the actual conditions the car is encountering and what you feel it is relaying during the braking zones. This should give you an answer, one other thing is make sure you check the wheel bearings as the extreme heat if it is that may be affecting the life of these parts. What do the rotors look like, are the surfaces front to rear the same or markedly different?

 

[YellowViperSRT10]

Lets go slow on your conclusion. More info needed. Is your tire diameter exactly the same as what the car was delivered with? Not tire, but dia. This is critical to brake temp since if the leverage changes it may cuase your rear axle to be doing more work than intended. Do you have the same pad compound being used on both ends? Do you know if your ABS is working properly? Tire dia. will also mess with your ABS and your front to back electronic biasing. Keep in mind that 65 to 75% of the brake load is is designed to be done by the front due to weight shift when decelerating and the reason you have big rotors and pads in the front. Are you fading, heat checking, rotor cracking or any other hot symptoms on the rear brakes? Pad wear is a square root factor of temperature causing pad life to be short when they run hot. Air ducting is not likely to be the solution, that is putting a band aid on the sore, lets find what is making the sore. There is a possibility your car has more stopping power in it than you are getting at this time due to the imbalance front to back in the brakes.

Bob,

Thanks for the reply. Hopefully we can diagnose this.

My past 7 track days I have been running my 19/20" setup on the track. The rear tire is a 345/25/20. Which has an overall diameter of 26.65. The stock 345/30/19 I believe is a 27.17 overall diameter.

Yes, I have the same exact porterfield R4 pads on all 4 corners.

The ABS is working fine, it has kicked in a few times and felt fine, at no time on the track did it kick in to early or late. ABS does not seem to be an issue here.

I feel no fade at all. The rotors are not cracked and still are in perfect condition with a lot more life on them. A few weeks ago at a different track at night I was running hard are instead of doing my usual cool down lap, we came right into the pits, and the rear brakes were smoking a little bit. So yes, its clear that the rears are running hotter then the fronts.

I will say however, (brake wise) the car feels incredible on the track with no fade or no rear bias at least felt by me or an instructor that also drove my car and a 100% stock 08 Coupe back to back..

 

[YellowViperSRT10]

I thought Homestead was a brake killer of a course? When was the last time you bled the brakes including the ABS module? If you have over cooked the fronts and there is air in the calipers/lines then the efficiency of that end could be compromised and the rears are taking more abuse than they should be. Do you feel the ABS activating at all on course? When and during what maneuvers? The cooling in the rear is obviously less than the front and if there are hard brake zones and short straights the rears may just be running overall hotter that the fronts and thus over heating the pads.

Bleed the brakes fully the next time out and pay mind to the actual conditions the car is encountering and what you feel it is relaying during the braking zones. This should give you an answer, one other thing is make sure you check the wheel bearings as the extreme heat if it is that may be affecting the life of these parts. What do the rotors look like, are the surfaces front to rear the same or markedly different?

Hi Mark,

Homestead is OK as for braking, It is somewhat of a little of a brake killer, but I have seen worse.

I never bled the brakes or ABS module at all! I been meaning to change the fluid, but I never got around to it yet. So its the same way it came from the factory.

I feel ABS activating when I am coming into a braking zone to hot and really getting on the brakes, it does kick in and help. It feels fine. I only feel it kick in on 1 or 2 of the braking zones where I am coming into from long straight about 120-130mph to make a hard turn. Again, this only happens sometimes when I am coming in to hot, but usually I avoid the issue all together.

I will try to bleed the system and put a good motul fluid in. Then provide feedback.

The front and rear rotors look virtually the same, and have about equal life left. There are no signs of anything strange. I inspect them well since when I come back from the track, the next day I usually put the stock pads on for regular street driving.

 

[mjorgensen Woodhouse]

Swapping the pads may be an issue Neal. The material on the rotors will be different and maybe the rears are being affected more that the front because they are not working as hard but burning more? The street material may also transfer from the rotor to the pads and act like the street compound in the rear thus overheating?

Stranger things have happened so just a thought to consider.

Take care,

Hi Mark,

Homestead is OK as for braking, It is somewhat of a little of a brake killer, but I have seen worse.

I never bled the brakes or ABS module at all! I been meaning to change the fluid, but I never got around to it yet. So its the same way it came from the factory.

I feel ABS activating when I am coming into a braking zone to hot and really getting on the brakes, it does kick in and help. It feels fine. I only feel it kick in on 1 or 2 of the braking zones where I am coming into from long straight about 120-130mph to make a hard turn. Again, this only happens sometimes when I am coming in to hot, but usually I avoid the issue all together.

I will try to bleed the system and put a good motul fluid in. Then provide feedback.

The front and rear rotors look virtually the same, and have about equal life left. There are no signs of anything strange. I inspect them well since when I come back from the track, the next day I usually put the stock pads on for regular street driving.

 

[Tom Shapiro]

I change and bleed my brake fluid (Motul 600) before every event. I use Mintex pads up front and stock pads in the rear and have had no issues.

 

[fireball]

Brake material is transferred from the pad to the rotor and it is this pad material to embeded pad material friction that does the braking. This is what you're doing when you 'bed' the brakes. You're loading the rotor with pad material.

When you change pads to a different compound you need to clean up the rotors so the embeded material, that doesn't match the new pads, is removed. It's simple to do. Either turn the rotors (only if required for another reason) or use emery paper and scratch the surface entirely until it changes color. Then go ahead and re-bed the brakes.

I suspect that this is the core problem here.

Greg