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Old 2018-10-04, 06:01 AM   #1
SanJoseUnicyclist's Avatar
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Location: San Jose, CA
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Disk Brake Heating Up

I'm riding with a Shimano BL-M445/7L Disc Brake from UDC. It's heating up on some longer/steeper hills (10% to 13% grade for ~1/2 mile) to the point that the disk gets warped and starts to rub on the caliper. About 10 minutes after the hill, the disk will cool off and go back to being flat enough that the rubbing stops.

Is this OK? Will I eventually ruin this brake?

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Old 2018-10-04, 06:18 AM   #2
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Disclaimer: I don't know the answer to your question.

I was going to comment that both of my disc brakes rub the calipers, but that doesn't change between heat and cold.

What I know about automotive brakes is that they get very hot very fast, but they also cool down relatively instantly. But this probably has little or nothing to do with a skinny rotor being applied for half a mile or more. That's a lot of constant use.
John Foss

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Old 2018-10-04, 07:03 AM   #3
Eric aus Chemnitz
Landesvertreter Sachsen im EVD
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A disc brake shall not rub. If your brake heats up too much, it is too weak for your use. What you can do is the following:
  • don't brake continously, give the brake some time to cool down as you ride.
  • bigger rotor/disc: bigger diameter, more braking power / less friction needed for same braking power, more material to heat up, more time of the revolution to cool down
  • ice tech rotor: better heat conduction
  • higher grade brake that allows ice tech pads with cooling fins
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Old 2018-10-04, 11:57 AM   #4
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Yes, it's a problem. As Eric said, you are overstressing the brake. Aside from the immediate issue you are experiencing, the excessive heat apparently leads to the seals degrading, and the brake leaking over time.

A bigger two piece rotor will help dissipate some more heat, and also not warp. Also, as mentioned, a higher grade brake with cooling fins will help.

But, as an immediate fix, intermittend braking, or just using it less hard will help too. I've seen people get their brake disks so hot that the steel discolored, if you just stay of the brake a bit you can probably prevent that.

A little rubbing of disk brakes however is normal, and in my experience doesn't wear down the brakepads much.
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Old 2018-10-04, 12:31 PM   #5
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Old 2018-10-05, 06:00 AM   #6
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Thanks very much, everyone. It's a really fun hill. Just at the edge of my abilities. Next time I ride, I'll try stopping part of the way down.

Makes me wonder how people ride down ski slopes or other long downhill trails...
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brake, disk, heating

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