[Yak] High Pressure Tires

[alex wetmore]

On Thu, 16 Apr 2009, Earl wrote:
> The BF came with 20 X 1-3/8 X 406 Continental Touring 2000 tires rated at 70
> psi. Inflating them to the max, I rode the loop with my wife, and noticed it
> was more difficult than on my road bike with 25 mm tires inflated to 120
> psi.  I had a hard time keeping up, when I am normally in front.  The bike
> came with two extra sets of Primo Comet 20 X 1.35 tires rated at 100 psi.  I
> switched to them,  and noticed a big difference on the next ride.  I had no
> trouble keeping up, and believe that it was almost as easy (but not quite)
> as my road bike. The tires made a big difference.

The biggest difference between the Conti Top Touring 2000 and the Primo 
Comet is the stiffness of the casing.  The Conti Top Touring 2000 has a 
very stiff casing that doesn't deform very easily.  Since it doesn't
deform very easily you waste energy doing so (that is rolling resistance).

The Primo Comet has a much lighter casing which deforms more easily and
this gives you lower rolling resistance.  You would feel this even if you
rode them at the same pressure as the Conti Top Touring.

This article gives you a good idea of how to pick a tire pressure for
a given tire size:
http://www.vintagebicyclepress.com/images/TireDrop.pdf

Note that this is written in the context of 650B and 700C wheels.  I
find that a little higher pressure works better on smaller folding
bicycle wheels.  So I might run my 40mm Scorcher tires at around 50psi
if they were on full size wheels, but I run them at a higher 60psi on
the little 349mm wheels of my Tikit.

The best (fastest and most comfortable) tires in my experience are
those with the most supple casing.  This often means that they are
sold with a lower maximum tire pressure, because the weaker (softer)
casing can't handle crazy high pressures.  For 349mm and 406mm tires
available today the Greenspeed Scorcher works well.

alex