What are my rotors telling me?

[thelostotter]

Question about optimizing brake pad selection. Last year I got to the point where the OE GT PP front pads were only lasting a couple events so I did some research and saw most people stagger the pads on these cars - 1 level more aggressive in front compared to the rear. I settled on Raybestos pads after doing a bunch of reading, these appeared to last a long time, be fairly gentle on the rotors, have good cold bite, and be difficult to overheat. I decided on ST45 front and ST43 rear pads and after 7 events I can say they do everything I've expected them to. Absolutely no complaints about performance and the pedal remains consistent for an entire 20 minute session.

But I've noticed a pattern after every session that makes me wonder if I've got a less than optimal setup right now. The front's always have a uniform transfer layer and heat checking while the rears always come off the track with bright, shiny rotors. I am not sure what this means? I've thought of two possibilities: 1) The ST45s are too aggressive up front doing the bulk of the braking, and ST43s front and rear may be more appropriate, or 2) The front pads are ok and the fault is the rears not being aggressive enough and I should try ST45 front and rear?

I didn't really start thinking about this until the drive home, the pictures below are the front and rears after the 200 mile journey home. The interesting thing is that rears have a totally uniform transfer layer after some street miles, and the fronts are cleaned up a bit but still have some heat checking.

Relevant info:
Castrol SRF fluid
GT PP with the 6 piston front calipers and Vorshlag cooling deflectors
Steeda two piece front rotors
Square 305/30R19 RS4 tires (soon to be NT01s if that influences what I should do going forward)

 

[JDee]

I think they're telling you everything is pretty ducky. They look pretty much like mine do, except I only ever buy blanks that are Ford OEM PP since I don't believe the 2 piece rotors are worth the cost for HPDE. But that's beside the point.
The heat checking on the front looks normal to me. Rears look fine as well. Those pads have a good reputation generally, though I've never used them just because they're very hard to source where I live.
If everything is working well I'd leave it alone, call it a win and move on to the next problem. There's always going to be a next problem it seems....

 

[302BOB]

There's always going to be a next problem it seems....

Murphy never goes on vacation............NEVER!!!!!!!!!!!!!!!!!!!

 

[thelostotter]

I think they're telling you everything is pretty ducky. They look pretty much like mine do, except I only ever buy blanks that are Ford OEM PP since I don't believe the 2 piece rotors are worth the cost for HPDE. But that's beside the point.
The heat checking on the front looks normal to me. Rears look fine as well. Those pads have a good reputation generally, though I've never used them just because they're very hard to source where I live.
If everything is working well I'd leave it alone, call it a win and move on to the next problem. There's always going to be a next problem it seems....

Thanks for the feedback. I should have added a third possibility, 3) Everything is fine.

Agree with you on the two piece rotors. When I first started tracking this car I was going through driver side rear wheel bearings every couple of track days. I thought it was heat related so I bought the two piece rotors to try and keep the hubs cooler. I had extremely poor luck with those rear rotors but the fronts have been ok. Those initial bearing failures must have been a fluke because the current one has been on car for 7+ events without any problems.

 

[bnight]

Thanks for the feedback. I should have added a third possibility, 3) Everything is fine.

Agree with you on the two piece rotors. When I first started tracking this car I was going through driver side rear wheel bearings every couple of track days. I thought it was heat related so I bought the two piece rotors to try and keep the hubs cooler. I had extremely poor luck with those rear rotors but the fronts have been ok. Those initial bearing failures must have been a fluke because the current one has been on car for 7+ events without any problems.

I'm going through driver side rear hubs like crazy even ordered new halfshaft for the left as I read it could be CV Joint. Besides brake pads and rotors what did you do for this issue to stop ?

 

[thelostotter]

I'm going through driver side rear hubs like crazy even ordered new halfshaft for the left as I read it could be CV Joint. Besides brake pads and rotors what did you do for this issue to stop ?

I started using some additional blue loctite and torquing the nut to 250 ft-lb. I use a new nut every time I change the bearing.

I run the car in advancetrac sport mode or advancetrac entirely off which I think is helping the rear brakes stay a bit cooler.

 

[blacksheep-1]

I agree with JDee, those brakes look fine to me.

 

[Ewheels]

@thelostotter I apologize in advance for stealing your thread but this may help others who have similar situations...

Same question as above, what are my rotors telling me?
Info:
2018 GT PP1
DBA T3 4000 rotors
G-Loc R12 pads
Motul RBF600
Vorshlag deflectors and DIY additional ducting
This was immediately coming off ACS (oval track notorious for being hard on brakes) (my rotors also clean up after the drive home)

 

[Dave_W]

Interesting that the speckled ring is where the two outer slots overlap in diameter. Slots are sometimes marketed as "cleaning up" the pad face. I wonder if the overlapping slots are "cleaning up" the pad a bit too much (i.e., making a slight groove in the pad there), so the pad pressure and/or temperature ends up being different in that area, leading to spotty pad material deposits. Just guessing.

 

[Bill Pemberton]

Another question as I find a R12 is not necessarily enough on front when on tracks that are hard on pads. Also are you using R12s on the rear as I definitely think you need a stagger ---- R8 or R 10. Frankly I would call up Danny Puskar ( Push Car ) at G- Loc and ask him what he thinks, as he may suggest moving up to possibly a R16 and using something like a 10 in the back. Right now your front pads may be working to hard if both are 12s as the rears may not be doing their part of the work --- just one of the possibilities.

 

[Ewheels]

Another question as I find a R12 is not necessarily enough on front when on tracks that are hard on pads. Also are you using R12s on the rear as I definitely think you need a stagger ---- R8 or R 10. Frankly I would call up Danny Puskar ( Push Car ) at G- Loc and ask him what he thinks, as he may suggest moving up to possibly a R16 and using something like a 10 in the back. Right now your front pads may be working to hard if both are 12s as the rears may not be doing their part of the work --- just one of the possibilities.

I currently have 12 front and 10 rear but as these pads are close to being toast, I'll be going to 16 front and 12 rear.

 

[Bill Pemberton]

I run 18s in front but like the 10s on the rear. You might consider 16 fronts and 10s rear , but do get them pre-bedded always!

 

[67GTA]

I run 18s in front but like the 10s on the rear. You might consider 16 fronts and 10s rear , but do get them pre-bedded always!

Agree with Bill here, albeit we’re both running S197’s. I’ve used R16/R12 for quite a while, and even with the Boss 302S ABS module, I was still getting a bit too much rear brake bias. Last weekend was the first on R10 rears - exactly what the car needed for balance.

 

[Ewheels]

Agree with Bill here, albeit we’re both running S197’s. I’ve used R16/R12 for quite a while, and even with the Boss 302S ABS module, I was still getting a bit too much rear brake bias. Last weekend was the first on R10 rears - exactly what the car needed for balance.

Interesting...
My rear R10s still have plenty of life, maybe I'll just get R16 front and save myself some money

 

[blacksheep-1]

Not sure how badly this would fake out the factory ABS, but I've run these in just about everything