Rear brake (caliper) temp questions

[IamFODI]

I have F8x brakes up front with the stock rears, so the rears are working a bit harder than they ordinarily would (pressure bias shifts rearward). I’ve had Alcon temp strips on the calipers for a few events this season; at the last one, they ended up 1-2 squares from maxed out (450º - 500º F / 230º - 255º C).

2008 E90 M3
~Stock weight
No aero
245f/265r AD09 (endurance 200TW)
Stock power minus whatever has escaped in >172k miles
PFC 331/332 pads, OE rotors


Questions:

1. Are these temp readings normal?

2. Any concern about dust boots and seals at these temps? This page seems to think so, but I’d value people’s lived experiences here as well.

3. Without swapping to different calipers, is there anything I can do to manage these temps? All I’ve seen so far is this brake duct kit, and I have yet to see any posts about it installed on an E9x M3, let alone how effective it is.

[kolosy]

Are you running dsc/mdm? That works your rear brakes a whole lot.

[IamFODI]

Originally Posted by kolosy

Are you running dsc/mdm? That works your rear brakes a whole lot.

Nope. Don't have MDM; DSC gets turned off after the first couple of sessions.

[amg6975]

I noticed this when trying out different pad compounds F to R. The Brake Force Distribution realizes the front is locking faster than the rear and sends brake force reward. I was cooking the rear brakes.

Maybe your brake balance being different with the F30 brakes is causing it?

[IamFODI]

Originally Posted by amg6975

I noticed this when trying out different pad compounds F to R. The Brake Force Distribution realizes the front is locking faster than the rear and sends brake force reward. I was cooking the rear brakes.

Maybe your brake balance being different with the F30 brakes is causing it?

Thanks for chiming in.

F8x, not F30 – but yeah, I'm sure that's what's causing it. Smaller effective piston diameter, so pressure bias moves rearward. And more brake torque up front with the stock staggered tire sizes, so fronts might be locking up faster.

When you say you were cooking the rear brakes, do you just mean faster wear on the rear pads? Or cooked seals as well?

What calipers do you have back there?

[amg6975]

Originally Posted by IamFODI

When you say you were cooking the rear brakes, do you just mean faster wear on the rear pads? Or cooked seals as well?

What calipers do you have back there?

Stock rear brakes (and front brakes.) They were just getting incredibly hot, like hard to check tire pressures hot. Pads and calipers were fine but it was the first time I've ever had wheel weights fall off my wheels from heat.

[IamFODI]

Originally Posted by amg6975

Stock rear brakes (and front brakes.) They were just getting incredibly hot, like hard to check tire pressures hot. Pads and calipers were fine but it was the first time I've ever had wheel weights fall off my wheels from heat.

Wow!

My rears definitely didn't get that hot. I had wheel weights falling off in front, but not in rear. Sounds like I still had some margin before seals started cooking.

Maybe these stickers aren't super accurate. ��

[omgzirra_exe]

I ran an Alcon BBK up front with OEM rear calipers for about a year before upgrading to the 2NH rear calipers and rotors. No issues at all during that time. I also ran the same pad compound front and rear PFC331/332.

Do not run brake ducts. I have no idea why people keep pushing for them. Unless they're done properly, you’ll end up with premature rotor wear or cracking. They're especially pointless on a street car.

The only real fix I can suggest is swapping your OEM rears for F8X rear caliper and rotors. That retrofit shifts the brake bias by about 4% more to the front if I remember correctly.

If not that, you might just be over-braking. Try bleeding off the brakes earlier and see if that improves your situation.

[aus]

I've seen a video where even with DSC off, there was still some rear brake activation.
.

[IamFODI]

Originally Posted by aus

I've seen a video where even with DSC off, there was still some rear brake activation.
.

I'd be super interested if you could post this. I know it's a thing for cars with "E-diff" functionality (open diffs), and I know MDM does it, but I was under the impression that off means off in this gen M3.

[bigjae1976]

When you upgrade the thermal capacity of the front brakes I would expect the rear brakes to get much hotter. If you're asking more from the front brakes, you're also asking more from the rear brakes unless you have a way to change brake bias.