Rear Brake Hotspots

[RedRocks]

I picked up brand new Carbotech XP10/8 pads for my 2008 S197 for SpeedVentures last weekend here in Vegas. After the event I noticed that the rear brake rotors looked pretty rough (see pic). A more experienced driver told me that the XP8’s are a bit too aggressive for the rear rotor and that I need to switch to a different rear rotor material. I have the Steeda 13” rear brake upgrade with the DBA slotted rotors. How do I know what material is better and where can I find that particular rotor? Options seem to be limited on the rear.

 

[Coz]

Seems hard to believe that an XP8 is too aggressive since that is one of their milder pads.

It looks like the pads were not bedded in properly prior to going out on the track.

 

[Coz]

Although I add that my statement is based on if the picture is showing uneven deposits of pad material.

If your picture is showing gouges and groves down into the surface of the rotor then that's a different story.

It's hard to tell which from the pic.

 

[RedRocks]

I followed carbotech’s bedding procedure and chocked car to let cool after. There aren’t any grooves that I can feel but occasionally I can hear the right rear (pictured) grabbing at slow speeds due to uneven transfer of material. I think I just need to try new rotors because I did not change the rear rotors before I went to the track, only fronts. Maybe it was due to incompatible pads...

 

[stuntman]

Way too aggressive. Overworks the ABS and causes that. Throw some Hawk HP+ or Porterfield R4S's on the rear and you're good to go.

 

[cobrarob]

Do you have the abs race module installed? Heard that makes the rear more aggressive like @stuntman said

 

[TheSpungos]

For what it’s worth, I run a much more aggressive pad in the rear - G-Loc R12 which is equivalent to Carbotech XP12 and I had not had any issue like that.

I did have that exact issue - excess pad deposits - on my fronts when I ran R10s up front the first time. The diagnosis from Danny Puskar (GLoc owner, formerly at Carbotech) was that it happened because I need a more aggressive pad, not less, and because I didn’t have a clean rotor (new or turned - no other pad material) to start with.

I am suspect of an XP8 compound being “too much pad” for a rear application. I think your issue was probably due to the prior pad material not being completely removed or some other existing blemish in the rotors.

 

[Coz]

If your rotors are not grooved I would not waste money on new rotors unless you want to keep a separate set of rotors for your track pads and your street pads.

Otherwise I would do one of two things:

Use scotchbrite on a drill with alcohol and clean your rotors.

Or

Drive around on the street with your track pads for a few days. Track pads can actually be more abrasive when they are cold and can remove the deposits.

Not sure why you chocked your car to let the brakes cool. Normally the end of the bedding procedure requires driving at normal speeds (while not stopping) to let the pads cool off. If you performed the agressive braking portion of the bedding process and then just parked the car with hot brakes, you could still have pad material deposited since the pads are still touching rotors (barely) even when the pedal is not pressed.

 

[RedRocks]

Don’t have the race ABS module just stock. I did the cool down I just didn’t wanna set the parking brake so I chocked it and let it sit for an hour. I’m gonna try the scotch brite and alcohol trick and see if I can get all the material off. If that doesn’t work I’ll try and get them resurfaced I think. I’ve been driving on the XP’s for a few days since I’m waiting for my new Bobcat daily’s to come in tomorrow.

 

[stuntman]

For what it’s worth, I run a much more aggressive pad in the rear - G-Loc R12 which is equivalent to Carbotech XP12 and I had not had any issue like that.

The rear tires have very little vertical loading under braking, so they don't contribute much or need much torque to reach the limit of grip under braking. A big wing helps a lot but if you don't have one, your rear pad is way too aggressive and putting a street pad on the rear will improve your braking performance.