| Re: New wheels, new tires (difference between 700x25, 26, & 28?)
David L. Johnson <david.johnson@lehigh.edu> wrote:
>On Tue, 15 Jun 2004 18:36:48 +0000, Dennis Ferguson wrote:
>> That is not how I understand it. If you take two tires which are
>> constructed the same, inflated to the same pressure and placed under
>> the same load, the widest tire will be the one with the least rolling
>> resistance since it is the tire which will deform the least at the
>> contact patch.
>
>Yes, but. Thing is, a bigger tire does not need, and usually is not rated
>for, as high a pressure as the skinnier tire. So, riding each tire at the
>rated max pressure, the skinny one will have less rolling resistance.
What you say is not untrue, but I think what you are describing may
not be a technology issue. That is, I don't think wide tires have
an inherent maximum pressure limitation sufficient to eliminate the
rolling resistance advantage of their geometry, it is in fact often
the case the tires built using the same technology (e.g. a single
series from a manufacturer covering a range of widths) will have the
same maximum pressure independent of width. For example, look at
Continental Ultra Gatorskin or Ultra Sport tires. The 700 mm/27 in
tires have the same maximum pressure rating for widths from 23 mm to 32 mm.
I think what you are describing is instead a market issue. The
tire buyers who are concerned enough about how their tires roll to
actually pay serious money for an advantage tend to be racers (or
wannabes). These are the same guys who value 23 mm or narrower tires
for their weight and aerodynamic profile, and generally have a low enough
body weight to ride tires that narrow, so it isn't surprising to me that
tires with the highest maximum pressure ratings and the best material
technology tend to only be available at the narrow widths these guys
want to buy. Its not that wide tires can't be high performance, and high
pressure, it is that the guys who are willing to pay for high performance
tires also want narrow tires.
In any case, I once had a tire blow off the rim on a long, steep descent
where I was riding my rear brake to keep the speed down while chatting with
a friend, an occurance I blamed (perhaps incorrectly) on my preference
for keeping my tires rock hard, so I'm no longer a fan of super-high tire
pressures no matter what the tire width. I generally run the same
pressure in the 23 mm tires on one bike and the 28 mm tires on the other,
so my argument at least works for me regardless.
Dennis Ferguson
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