## Heat dissipation from a brake pad

Hi all,
(this has originally been in the Materials and Chemical Section. I think it does not belong there).

I'd like to add a question heat dissipation from a brake bad. Basically, let's assume a brake pad is pressed against a surface that quickly moves along (can be the bicycle brake pad on the wheel rim or, in the case of an inline skate with a heel brake, a brake pad and the road itself. Let's look at the latter example in the following). Consider a quasi-stationary case: rolling down a long decline with constant slope and speed. So we have to dissipate some constant power (in the order of a few hundred Watts [10% slope - 10m/s speed - 1 m/s vertical speed - 80 kg mass - 800 N weight - about maybe 50% power dissipated into air friction - makes 400 W]).

In a first order approach I would say that the brake pad would not heat up higher than the temperature of the road. Because that road surface moves along quickly, it does not heat up significantly while the pad glides along. The temperature at the interface road/pad is thus constant. This is where the heat is generated. So the road basically acts like an infinite and "zero-resistive" heat sink.

I think experience does not support this approximation. In particular, if you have an inline skate with a heel brake, the heel brake DOES heat up (does it?). How much? What's wrong with the first order approximation? What would be a more realistic model?

Thanks, Hanno
 PhysOrg.com engineering news on PhysOrg.com >> NASA: Austin, calling Austin. 3-D pizzas to go>> Research suggests modular design competence can benefit new product development>> Army ground combat systems adopts tool for choosing future warfighting vehicles
 Many thanks. A lot of good points! I'm now out for 3 weeks summer vacation. Will do some practical experiments! If anything useful comes out, I tell you. Hanno

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## Heat dissipation from a brake pad

ezskater, I'm not sure I've understood.

In the case of a bicycle, the braking is done at the surface of the wheel rim. If you touch a wheel rim after braking down a long decent, you'll burn your finger. It does get hot. The friction between the tyre and the road here is irrelevant, as long as the wheel remains spinning whilst you're slowing down.
 Blog Entries: 7 Recognitions: Gold Member Homework Help Science Advisor Brewnog, Note that the question ez asked about and the responce I gave him regards the brake pad on a roller skater where the pad is in contact with the road, or more ideally, a flat surface. I think the case of a brake pad on a disk or wheel rim is more interesting actually, but I didn't start this post! LOL
 Yes, sure the rim gets hot. But does the brake pad itself get HOTTER than the rim? And by how much? (In the case of a skate braked by a friction heel brake, rim ==> road. So the difference is that the rim comes back to your pad with every revolution of the wheel, while the road doesn't. You always get "fresh cool road" and don't care about the heat you leave behind!) Hanno