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Old 2018-10-04, 06:01 AM   #1
SanJoseUnicyclist
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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?

Thanks!
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Old 2018-10-04, 06:18 AM   #2
johnfoss
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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.
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Old 2018-10-04, 07:03 AM   #3
Eric aus Chemnitz
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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
finnspin
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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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https://www.google.com/search?source...isc+brake+drag
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Old 2018-10-05, 06:00 AM   #6
SanJoseUnicyclist
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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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Old 2018-10-05, 02:09 PM   #7
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Quote:
Originally Posted by SanJoseUnicyclist View Post
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...
On ski slopes, the snow will cool down the brake :P
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Old 2018-10-05, 02:43 PM   #8
finnspin
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Quote:
Originally Posted by SanJoseUnicyclist View Post
Makes me wonder how people ride down ski slopes or other long downhill trails...
Good rotors help a lot. I've never had overheating issues this far, even in the alps. But those have always been group rides, so every few miles at least you take a break to let the rest catch up, and technical on the downhills, which you go relatively slow on, giving the brake chances to cool.

Where I've seen people get them very hot (including the mentioned discoloured disk, and a very distinct smell of overheated pads) is things like ski slopes, or gravel roads downhill, where you go downhill fast. But I think most people just don't ride those as much as you think, because they get boring after a while. If you spend all the time hiking up a hill, you either like to enjoy the view going downhill, or ride something challenging.
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Old 2018-10-05, 06:54 PM   #9
pierrox
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What's your wheel size? And rotor size?
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Old 2018-10-05, 09:46 PM   #10
bouin-bouin
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Quote:
Originally Posted by pierrox View Post
What's your wheel size? And rotor size?
and your pad quality ?
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