On Thu, 29 Jan 2009 18:21:50 GMT, John Forrest Tomlinson
wrote:

On Thu, 29 Jan 2009 10:12:44 -0800 (PST), Chalo
wrote:


The faster you ride, the more you need in terms of rim protection,
shock absorption, wear resistance, pinch flat resistance, and
traction. So the faster you go, the more you can benefit from a wider
tire.

I can see that for traction, though very few people go near the limits
of traction on moderatley narrow tires.

But why do you need more for rim protection when going fast?

[snip]

Dear John,

The faster the hammer hits the nail, the deeper the nail goes into the
wood.

More rim protection is needed at higher speeds because impact roughly
corresponds to kinetic energy, which is half the mass times the square
of the velocity--it rises even faster than the speed.

At 20 mph, a rider hits a chunk of gravel (oops!) with an impact of
20^2 whomps, or 400 whomps.

At 25 mph, the same rider hits the same chunk of gravel at 25^2
whomps, or 625 whomps.

At 30 mph, he hits it at 30^2 whomps, or 900 whomps, more than twice
as hard.

That's why drivers slow down on rough roads and why faster riders get
more pinch flats on bicycles.

Cheers,

Carl Fogel