[M3SQRD]

Originally Posted by David1

Here is a pic of how grooved they are but they work fine.

The 1521 is a street-only pad and it is not designed to handle the higher temps of autox and the track. You’ve likely glazed the pads from overheating them. Still not sure what’s caused the grooves but it could be a result of fading them but that typically glazes them. I assume the rotors had oem pad material on them before installing the 1521? Did you bed-in the 1521 pads?

[medphysdave]

Originally Posted by M3SQRD

Front looks a little better than the rear. Rear has a faint layer of material. A rebedding procedure will likely improve your street braking and minimize the oh 💩 events. I ran the brake bias calculation of the 2NH brake setup and was surprised that the front is 67.6% vs. the f8x blue calipers and 380/370 rotors is 62.8% front. An almost 5% shift forward is significant. It explains why Essex created a kit specifically for the f87 M2C which is within 0.2% of the stock bias.

I'm running a 380mm rotor up front. Not sure what difference that makes.

[M3SQRD]

Originally Posted by medphysdave

I'm running a 380mm rotor up front. Not sure what difference that makes.

Is it the 2NH calipers with F/R 380/380 mm rotors? That’ll shift the bias rearward a bit due to the reduced mechanical advantage of the F calipers. I may have looked at 2NH with 380/370 but not 380/380.

[medphysdave]

2nh is normally 400mm front. I'm running a custom adapter to run the 2nh caliper with 18" wheels.

[M3SQRD]

Originally Posted by medphysdave

2nh is normally 400mm front. I'm running a custom adapter to run the 2nh caliper with 18" wheels.

Your brake bias is 65.6% on the front vs 67.6% front for stock 2NH - 2% shift rearward which is good.

[David1]

Originally Posted by M3SQRD

The 1521 is a street-only pad and it is not designed to handle the higher temps of autox and the track. You’ve likely glazed the pads from overheating them. Still not sure what’s caused the grooves but it could be a result of fading them but that typically glazes them. I assume the rotors had oem pad material on them before installing the 1521? Did you bed-in the 1521 pads?

They went on the car at around 800 miles.

[M3SQRD]

Originally Posted by David1

They went on the car at around 800 miles.

If you can, I’d pullout one pad and look at the condition of the pad compound. If it is really shiny the pad is glazed. You’ll have to pullout all pads and start with a coarse sandpaper and finish it off whine a fine sandpaper when the surface looks dull. The pad material also can be cracked when overheated. If there are significant cracks running completely across the pad then it creates a safety issue.

If the pads look fine then I’d strongly recommend rebedding them even if XP12 was already on there. With only a small amount of running the XP12 on the street then there’s a good chance the pad material was worn off.