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**Matt O'Toole**

On Tue, 10 Oct 2006 12:46:37 -0600, wrote:

jim beam wrote:

wrote:

- After playing with the brakes for a few minutes, I noticed that
the
discs get noticeably warm, around 170F. Are there ever heating issues
with disc brakes on longer downhill segments? Seems a stupid
question, but they did get quite warm just by playing around on level
ground for about ten minutes.

they get warm because of the friction - that's what all brakes do.
you'll have no problem with heating issues on a disk braked bike - once
set up correctly, use with complete confidence.

Regarding the heating issue, I came across a couple on a tandem who had
a hydraulic disk brake in back, instead of a drag brake. They said that
on long downhills the brake heating transfers heat to the fluid, the
fluid expands and they end up with the brake applied without any lever
action. They have to stop and let the fluid cool.

I'm not surprised. Tandems have double the weight and therefore double
the energy to be dissipated while braking. If the brake components are
not upgraded to compensate it's likely they'll overheat. There are
tandem-specific disks for this reason. But because it's a smaller
market they may not be as well-developed as single MTB brakes -- which
also had overheating problems in their early days.

A tandem drag brake and a downhill ATB are not the exact same situation
but both can expect to sometimes apply the brake for 20-30 minutes on a
very long downhill. Does this ever occur on an ATB?

Yes. As I said, overheating was common with the first generation of
MTB disks.

The best "disk" is your rim, but overheating it can cause tires to blow
off, which is the reason for drag brakes at the hub on tandems.

Matt O.

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