>I think all the studies have shown that the aerodynamic resistance
>increases somewhere around 20 MPH so that the wider tire loses that
>roll fast advantage.
We tested different tire width in the wind tunnel, and found that the differences in wind resistance between a 25 and a 32 mm tire were lost in the noise.
The rolling resistance differences between different-width tires are significant, but they depend very much on the road surface. The rougher the road, the wider a tire is ideal. So any generalized statements on which tire is fastest is misleading. There appears to be little doubt that all things considered, a 25 mm tire is faster than a 23 mm tire on average roads, even at racing speeds. When you draft in a peloton, the aerodynamic issues are greatly reduced, anyhow, so you can ride an even wider tire. (If you are a break-away specialist, you are more concerned about aerodynamics...)
On cobblestones, a 38 mm tire will be much faster than a 25 mm tire - we tested this, too, when we measured suspension losses.
A couple of years back, Chuck Schmidt posted a report to the iBob list indicating many track riders now use 23-24 mmm tires... see
http://search.bikelist.org/
For a track bike, 24 mm probably does qualify at "fat."
Jan Heine Editor Bicycle Quarterly 2116 Western Ave. Seattle WA 98121 http://www.bikequarterly.com
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