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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
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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
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What's your wheel size? And rotor size?
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Old 2018-10-05, 09:46 PM   #10
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What's your wheel size? And rotor size?
and your pad quality ?
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Old 2019-04-11, 09:54 PM   #11
SanJoseUnicyclist
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My brake continues to heat up on this downhill section. It's a fun hill that I want to keep riding.

To answer the question above, I'm riding a 2018 29” KH from Unicycle.com (with the Nimbus hub to get the disk inside the frame). My disk rotor size is 180mm diameter and 1.8mm thick. Pad quality is probably pretty good -- I've had the muni for less than a year and the brakes have not seen a ton of use.

Does anyone have any experience with putting the Shimano Ice Technology disk brakes on a muni?

If so, I'd really appreciate knowing exactly what you bought that worked with the muni.

Thanks!

Last edited by SanJoseUnicyclist; 2019-04-11 at 09:55 PM.
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Old 2019-04-12, 06:31 AM   #12
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Hi,

actually the 180mm rotor is fine.

However it is a bit more complex. The BL-M445 is using a BR-M447 caliper. This caliper has plasic pistons which only allow the usage of resin pads. Sintered pads could actually take more heat, but also heat up the pistons and calliper more which will not work with the plastic pistons.

I am not sure on all the Shimano models, however at least from the SLX and higher grade, they all use ceramic pistons. Then you can use sintered pads as well.

Bottom line: If you significantly want more brake power and way better fading resistance, you will likely have to go for an upgrade of your brake.

As an example: We found the same issue when going down a steeper, long decent on a Muni tour. While my Shimano Saint did not have any issues, another brake (BR-M447) showed the discoloured rotor and started smelling, although the riders weight (she) was at least 20kg less than mine.
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Old 2019-04-12, 07:48 AM   #13
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My starting point would be a two piece rotor. I have a Formula 180mm one, but I don't think the brand matters. It allows movement between the friction surface and the center, which helps it not warp. Also the aluminum center is better at transfering heat than steel. When I stop with hot brakes, I can hear the two parts moving (little ping sounds) as the outer part cools.

If that doesn't work, it's likely time for a new brake. If you want to do Shimano Icetech, I've heard of great experiences with the Shimano Saint M820. Pricey, but good.

I'd expect any "downhill" mountainbike brake to work well, you just need to choose one you like. Mountainbikes go way faster than us, so even though they have two brakes, they put theirs through much more stress than we do. Anything you read on mountainbike reviews, other than ergonomics can be directly applied to unicycles. With modern brakes, they all seem to fit well on the caliper side with the inboard brakes, the only concern is how the master cylinder fits under the saddle. For example, I recently test fitted a Sram Guide R, and the handle just doesn't really work on a unicycle.
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Old 2019-04-12, 09:04 AM   #14
Eric aus Chemnitz
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Quote:
Originally Posted by SanJoseUnicyclist View Post
... I'm riding a 2018 29” KH from Unicycle.com (with the Nimbus hub to get the disk inside the frame). ...
so you're using a d'brake and thebrake on the left, right?
Quote:
Originally Posted by SanJoseUnicyclist View Post
... Does anyone have any experience with putting the Shimano Ice Technology disk brakes on a muni?

If so, I'd really appreciate knowing exactly what you bought that worked with the muni.

Thanks!
I run a SLX with IceTech (Pads as well as rotor) on my 24" Muni with 160mm rotor. It works fine for me and i never had any issues. (But i do not ride the hardest downhills.) I've one of the first generation IceTech rotors that were one piece, so the whole thing was plug and play with my Spirit cranks. The newer ones have some plastic parts on the spider that do not work with spirit cranks without filing/grinding something off. For inboard disc, the new gen. rotors shall also work plug and play.
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Old 2019-04-14, 04:09 PM   #15
SanJoseUnicyclist
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This is all super helpful, everyone. Thank you!!!!

Eric, I am using the d'brake on the right side (I think it's right. It's the side that the d'brake was designed for). Sort of a bummer because I can't use the little cable tie brackets built into the left side of the KH frame.
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