Blowing tube descending

On Sunday, April 23, 2017 at 9:24:24 PM UTC-7, OSHA wrote:
On Sun, 23 Apr 2017 21:06:44 -0400, Frank Krygowski wrote:
On 4/23/2017 4:48 PM, wrote:
It doesn't seem to me that the discussion is taking into account the fact that the bike's kinetic energy (to be dissipated by the brakes as heat) is proportional to its velocity squared. So it is better to keep your velocity as low as possible, right?

Keeping your velocity low is one way to prevent blowouts from
overheating brakes & rims. Letting your velocity get very high is
another, assuming the road allows that. At high speeds, the aero drag
does a lot of the braking for you. If you're gutsy enough, you may not
need to use the brakes at all.


A long time ago one of the technical mags (Cycling Science? Bike
Tech?) had an article where the author did a bunch of calculations to
characterize heat generated while braking and then found the maximum
to be about 1/2 the free decent velocity. (So, if you descend a hill
at 30 kph without any braking, maximum heat will be generated when
holding the bike to 15 kph).

Sadly, I don't recall the actual math.

I believe you will find that it's a bit more complicated than that. I will have to think about this but presently am in an argument about quantum physics.

On 4/24/2017 4:45 AM, John B Slocomb wrote:
On Mon, 24 Apr 2017 04:21:11 -0000 (UTC), OSHA
wrote:

On Sun, 23 Apr 2017 21:06:44 -0400, Frank Krygowski wrote:
On 4/23/2017 4:48 PM, wrote:
It doesn't seem to me that the discussion is taking into account the fact that the bike's kinetic energy (to be dissipated by the brakes as heat) is proportional to its velocity squared. So it is better to keep your velocity as low as possible, right?

Keeping your velocity low is one way to prevent blowouts from
overheating brakes & rims. Letting your velocity get very high is
another, assuming the road allows that. At high speeds, the aero drag
does a lot of the braking for you. If you're gutsy enough, you may not
need to use the brakes at all.


A long time ago one of the technical mags (Cycling Science? Bike
Tech?) had an article where the author did a bunch of calculations to
characterize heat generated while braking and then found the maximum
to be about 1/2 the free decent velocity. (So, if you descend a hill
at 30 kph without any braking, maximum heat will be generated when
holding the bike to 15 kph).

Sadly, I don't recall the actual math.

Didn't Brandt participate in some brake/temperature tests? I seem to
remember mention of it but I never read any results.
IIRC, he was tinkering away on that project about the time he had his
final crash. I don't think it got far enough to have noteworthy results.


--
- Frank Krygowski