Re: Nobody knows about RR

James Scott said:

Conti doesn't know anything about RR...until/unless they have something
new to sell.

http://www.cyclingnews.com/tech/?id=2005/features/conti_tech

This article (really an ad for new Conti 25mm tubs with a Vectran
anti-puncture belt) actually has a little discussion of RR vs.
aerodynamics plus a nice visualization of contact patches for fat vs
narrow tires.

JLS

Dear James,

That's an interesting article--thanks.

I notice that the second graph comparing the 19mm, 22mm, and
25mm tires shows a dramatic 40% rolling-resistance drop,
from 0.60 down to 0.36 for the widest tire.

But that's with all three tires inflated to the same 8.5 bar
pressure, which is around 123 psi. I think that Sheldon
Brown would argue quite plausibly that few riders use the
same inflation for 19mm and 25mm tires, which rarely have
the same real limits, anyway. Darned few pros are using 125
psi on long tours.

I also notice that the bottom graph is a bit misleading. It
shows that less power is needed for the thinner, more
aerodynamic tire at 50 km/h, which is probably true.

But few of us cruise for long at 31 mph.

And the graph gives the impression that the 19mm tire
requires less than 50% as much power by showing only the
very end of the two bars. The numbers, however, show that
the thinner tire actually requires about 95% as much power,
something like 374 watts vs. 392.5 watts.

The contact patch diagrams are nice, but I end up wondering
if they're ignoring something practical.

In a pure, idealized rolling-resistance test on a smooth
drum, the rounder contact patch of the fatter tire reduces
sidewall flexing and rolling resistance.

But on a real-world surface with irregularities, the longer,
skinnier contact patch of the thinner tire should bounce and
pitch less for the same reason that a longer ski or
wood-plane (or tandem) follows a gentler path--and the
gentler path reduces real-world rolling resistance.

Carl Fogel