On Thu, 25 Jun 2009 07:38:19 -0700 (PDT), Andre Jute
wrote:

(snip)

Hell, consider this sequence of facts. Jobst reported the other day
that he got up to 50mph or 80kph down some notorious mountain in
California. If his brake pads faded, never mind failed to stop him
(or melted!), you can bet we would have heard of it. I needed truck
assistance to get up to 100kph, and had to stop in a hurry afterwards
to avoid crossing a dangerous intersection (or, as bad, hitting the
back of my own truck). Neither disc brakes nor roller brakes got too
warm to touch.. I didn't at the time have a bike with rim brakes but I
do now and often ride the brakes down long descents so as not to speed
ahead of my pedalpals -- result: at worst a slightly warmed rim. Hard
braking from over 50kph at the bottom of a hill makes no impression
either, as I've reported here before.

(snip)

Data point: 220 lb. rider, reasonable 700c rims (Alex DM-18). Coming
down Gannett Hill
http://www.mountainzone.com/mountain...sp?fid=6276756
the road isn't too straight and there is a deep ditch on either side.
I kept speed down to 20 mph.

Both rims were very hot at the bottom. How hot? Wish I knew. It
wasn't boiling, but uncomfortable to the touch. The temperature
measuring strips are a good idea.

Now scale the hill up to Rocky Mountain size...