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Techniques for avoiding overheating brakes?(10 posts)

Techniques for avoiding overheating brakes?LC
Jul 31, 2001 7:48 PM
I have been doing some really big hills lately and twice now I have blown my tube coming back down from excessive heat. I have to wait 5 to 10 minutes before I can even touch the rims, so I have got major heat build up. Both times the front tube blew right at the bottom of the hill just as I stopped. Is there a technique for braking that I could use to avoid this? The hills have some sharp curves and then a stoplight at the bottom of the hill, so I do have to use the brakes.
re: Techniques for avoiding overheating brakes?Car Magnet
Aug 1, 2001 1:34 AM
Try alternating brakes. Squeeze rear, release, squeeze front, release, repeat as necessary. Don't overbrake!! This will allow for one brake to cool while the other is braking. It will take some practice to know how long for each one depending on your bike, speed and grade of descent.
best reason for disc brakeskenyee
Aug 1, 2001 6:13 AM
But there are none in production for road bikes :-P

Would different braking surfaces help dissipate the heat better?
Simply go slower.Steeeve
Aug 1, 2001 7:58 AM
The way to avoid overheating is to never go too fast. Going slower down the hill will give more time to allow the heat to dissipate from your rims. If you blast down the hill at a high speed and then stop quickly, all the heat is put into the rims at once. Going slower down the hill (by applying the brakes while going down the complete hill) will start the heat dissipation much earlier (thus the longer period of time for heat dissipation). It's really that simple.

I suppose there may also be some brake shoes that have a larger heat-sink (such as alunimun shoe with fins), but most of the heat is still taken up by the rim because the brake pad material itself (rubber or other organic compound) have very poor heat conductivity. So even these brakes are not a good answer.
use 'em, don't ride 'emD'Ohhh!!!
Aug 1, 2001 8:04 AM
gotta lay off the brakes
Aug 1, 2001 1:39 PM
I've ridden down huge mountain passes with steep descents and sharp curves and never overheated my brakes. I certainly haven't melted any tubes. This guy is just using them too much.

Modulate your speed by feathering the brakes periodically, so you don't have to bleed off so much speed when you hit a sharp curve. And don't use the brakes at all on a shallow curve. Just lean into it.
re: Techniques for avoiding overheating brakes?Jofa
Aug 1, 2001 2:09 PM
I've blown tubes from braking in the past as well. The reason is that the braking generates heat which in turn causes the tyre pressure to increase. The maximum pressures molded on tyre walls are quite genuine: exceed them by 10-20% and you risk the tyre blowing off the rim. The solution in this case is to drop your tyre pressure by 10-20% before a big descent, if you currently run your tyres near their maximum pressure. Anything under 100psi for most modern tyres of 25mm or less should be fine. If you don't have a guage (and who has?), then let out air until the pressure is such, by feel, that you wouldn't ordinarily go riding on it.

One partial solution to the problem, in use, is to douse the rim in water from your water bottle. This will have a significant cooling effect, as well as an energetic hissing if the rim temperature is high enough.

Pumping the brakes will only be useful if it's to spread the force between the front and the rear, where it might not have been. Pumping just one brake or the other instead of applying it evenly does no good.... you'd be best to stop every few minutes: if the descent is that fierce then it surely offers some spectacular views as well.

I've only ever had this problem when riding in the Pyrenees and I think once in the Alps, and I live in neither; I'm sure there are many long descents to rival either of these ranges in the States, but I wouldn't want any novice riders reading this to think that it is a perpetual problem. Bicycle brakes of ordinary design work fine in 99% of circumstances, enough to offset the dubious advantages of additonal disc brakes.
re: Techniques for avoiding overheating brakes?Car Magnet
Aug 1, 2001 2:29 PM
I stand corrected. I should have said "feather" the brakes to slow the bike on the descent. Jofa explained the technique more precisely. I guess I'll wait on my coffee to kick in next time.
I don't see where you think you were wrongJofa
Aug 1, 2001 3:27 PM
You said: 'Squeeze front, Squeeze rear, repeat'. I think this is good advice, because it spreads the braking effort between two brakes and rims where it might have been confined to one, in a circumstance where the ultimate power which only the front brake can manage is irrelevant. Frequent advice however runs along the lines of- ' pump the front brake, so that it has some time to cool off inbetween goes', and it was this erroneous advice which I was meaning to forestall. I'm sure your coffee was working fine.
re: Techniques for avoiding overheating brakes?LC
Aug 1, 2001 9:08 PM
Thanks for the tips. I never have this problem on mountain passes since I usually don't have to make 3 full stops down a 20% grade and highways are not that steep anyway and you can just let it go and trust your tires to grip in the corner. In city hills are a whole new ballgame and I think I may just have to find a different hill to train on before I blow a front tire while screaming down that hill. New riders would never have to worry about this since they would never make it up there anyway.