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**Marz**

wrote:
jim beam wrote:
wrote:
Hi,

- 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.

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?

I've never had heat cause the brakes to apply through heat expansion.
What I do experience is dot4 brake fluid boiling (or the water in the
fluid boiling) and I loose all braking power. And I have to wait until
it cools before continuing down hill. On the same hill with v-brakes I
had a front tire blow because the rim got too hot.

My make of disk brake is not compatible with dot5 fluid, which if I
could use it, would help.

Here's a question, which action produces the most heat, keeping the
brakes on to control speed on a steep hill or letting the bike go and
then jamming on the brakes at the last second to kill the speed?
Laters,

Marz

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