On 2008-03-28, Marz wrote:
On Mar 28, 3:49 am, Ben C wrote:
On 2008-03-28, Ben Kaufman wrote:
[...]
Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

From hayes...

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils. An important characteristic of
brake fluid is that it is incompressible. When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power. Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil. If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling. Once the pressure is released,
the fluid will instantly boil and fade will occur."

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

I have heard of fluid fade affecting bicycle brakes before. It is
shocking in my opinion because that's the easiest kind of fade to fix--
you just need brake fluid that doesn't boil, which exists. There's no
tradeoff or anything, it's a win-win no-brainer. Cars haven't suffered
from fluid fade for years with modern decent brake fluid.

I mentioned this before and someone said it's because bicycle brakes use
crappy brake fluid because it doesn't strip the paint. My advice: use
proper car brake fluid in your bike brakes but pour it in carefully and
don't spill it.