Very hot rear wheels compared to front

[ShaunG]

Hi Everyone,

I have a E46 M3, ground control/koni 2 ways, 265/35/18 Hanook Rs3's, Brembo Gt 6 pistons in the front and 4 pistons in the rear. Pads are Hawk DTC70 frong and DTC60 rear.

I've owned this car for about 4 years and it's only goes to the track but is street legel. I have run into a strange issue, the last two track days after each secession the rear wheels are so hot you can't touch them. The fronts are hot as well, but not as hot as the rears. I've tracked this car many times and never had this issue. When this issue first occurred last summer. I rebuilt all the brakes but again at the last track day I had the same issue after every secession VERY hot rear wheels and hot front wheels. When I say very hot, I mean you can not touch them with a bare hand and even with gloves on you can feel the heat.

I run the TC/DSC off but it feels like DSC might still be on? That would explain hot rear brake and I'm off my times and can't figure out why. I thought that was not possible with E46 M3 and it was a single button push to disable both? I have no dash error lights.

Anyone else experienced this?

Thank you!

[eacmen]

Since the power is being sent to the rear wheels they should get hotter than the fronts. Track surface temp also has a huge influence on how hot the tires get.

- All four tires set to the same cold pressures? Did the rear tire pressures change more than the front after a session?
- Did you change tire compounds?
- Was the track surface temp the same between the days/sessions you're comparing to?

[ShaunG]

All same pressures.
I changed compounds
it was cooler out.

I was at a road course, not a drag strip.

[Slideways]

What about the brake shoes and handbrake adjustment? Maybe the handbrake is slightly engaged?

[ShaunG]

What about the brake shoes and handbrake adjustment? Maybe the handbrake is slightly engaged?

That's something I also thought about but, I have to pull my hand brake ALL the way up to get it to engage.

[eacmen]

I am thinking this may not be a problem. Just might be how those tires are. Even with a cool down lap our RE71s will still be hot enough to pick up rocks in the paddock and I would not touch them with my hand.

Check the rear brakes just for sanity's sake to make sure the pistons aren't seized. Could also check the wheel bearings but I feel to generate that much heat they would be *very* noisy.

Next time you're at the track go up to one of the folks with a trailer, one of them is likely to have a tire pyrometer. Check the outer, middle, inner edge of the tread - record the data and report back. Or if you're in a spendy mood you can get one for yourself, its useful to verify alignment is good. I have seen folks leave them at pitout stand, then pit in mid lap and get readings fresh off the track (more accurate than after cooldown and parking in the paddock).

This is the one I have: https://www.amazon.com/Longacre-52-5...dp/B000FPVU5O/

[Slideways]

That's something I also thought about but, I have to pull my hand brake ALL the way up to get it to engage.

Yeah, I'm not sure what else it could be. There is not much else back there to check besides the brakes, wheels and tires. I noticed that you have a MK20 equipped car and you posted that you have a related fault code. Maybe there is an issue with the module. I remember Dr. 3VIL on M3F had an issue with his 02 MK20 where he had to tow the car home from the track due to an issue with something intervening making the car undrivable. I'm pretty sure he would turn off DSC on track as he was a pretty experienced driver.

[ShaunG]

Yeah, I'm not sure what else it could be. There is not much else back there to check besides the brakes, wheels and tires. I noticed that you have a MK20 equipped car and you posted that you have a related fault code. Maybe there is an issue with the module. I remember Dr. 3VIL on M3F had an issue with his 02 MK20 where he had to tow the car home from the track due to an issue with something intervening making the car undrivable. I'm pretty sure he would turn off DSC on track as he was a pretty experienced driver.

Dr. 3VIL had an awesome looking car. The guy swapped wheels like I change clothes.

I think the DSC is staying even when it's supposed to be off. The only way the rear wheels are getting hot as they are is because the rear brakes are engaging. I've disconnected the battery and cleared all the codes. I will be a the track in 2 weeks and will pull fuse 61 if after the first secession if the issue continues. With street driving it's completely fine.

[ShaunG]

I am thinking this may not be a problem. Just might be how those tires are. Even with a cool down lap our RE71s will still be hot enough to pick up rocks in the paddock and I would not touch them with my hand.

Check the rear brakes just for sanity's sake to make sure the pistons aren't seized. Could also check the wheel bearings but I feel to generate that much heat they would be *very* noisy.

Next time you're at the track go up to one of the folks with a trailer, one of them is likely to have a tire pyrometer. Check the outer, middle, inner edge of the tread - record the data and report back. Or if you're in a spendy mood you can get one for yourself, its useful to verify alignment is good. I have seen folks leave them at pitout stand, then pit in mid lap and get readings fresh off the track (more accurate than after cooldown and parking in the paddock).

This is the one I have: https://www.amazon.com/Longacre-52-5...dp/B000FPVU5O/

I have a tire pyrometer. I'll take a measurement next time, but it's the wheel and brakes that area hot, not so much the tire.

[eacmen]

I have a tire pyrometer. I'll take a measurement next time, but it's the wheel and brakes that area hot, not so much the the.

I misunderstood. Probably issue with the rear brakes then. Either there is too much rear bias or the pistons are seized.


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[ShaunG]

After speaking with a very knowledgeable tech/racer he stated that the E46 M3's with front and rear Brembo big brakes kits have rear bais issues.
I have a full race pad on the rear and he suggested two things. One, sell the rear brakes and go to stock setup or keep the rear Brembo kit and remove the race pad and get a cheap street pad. I ordered a cheap street pad and will post the results.

[Slideways]

Are you using race pads on all four corners? Having a more aggressive pad only in the rear could explain your issue. p0lar posted this brake bias chart for both pre and post MK60 a while back. If I am reading the chart correctly, the stock MK20 cars has more rear bias than the MK60. Most of the Brembo kits are front bias though -

https://thebuildjournal.com/tech-gui...-chart-e46-m3/

[eacmen]

Might be good idea to take the piston bore sizes and throw it into the brake bias calculator.

https://docs.google.com/spreadsheets/d/1RvbjuaHjpRbLzNMQ-5AbIk2iiVMBb3Ofn53HEsyKDC8/edit

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