At 4:01 PM +0000 11/4/08, billydavid13@comcast.net wrote:
>My guru in a
>ll things technical, Jan Heine, makes good arguments for sewups being faste
>r in BQ and i buy them. My point is that despite all the hype and measureme
>nts purporting to show clinchers being faster, racers "vote w/ their feet"
>by choosing tubulars.
Sorry, there is a misunderstanding. Our real-road tests seem to indicate that clinchers are slightly faster than tubulars.
We ran three tires that were sort-of-similar:
- Clement Criterium tubulars (one silk, one polyester), 21.5 mm wide - Deda Tre Giro d'Italia clincher (made in the same Clement/Challenge factory as later Clements), 24.5 mm wide - Clement Campionato del Mondo tubulars (polyester), 28 mm wide
All of these tires appear to use similar casings. It is possible that the Del Mondos use a slightly coarser (less tpi) casing.
Note that wider tires were slightly faster in our tests. We tested 3 Michelin Pro2 Race tires, and the 25 mm was fastest, the 21 mm (nominal: 20 mm) slowest. So you'd expect the Campionato del Mondo to be fastest, all things being equal.
The times were
- Criterium: 27.4 seconds - Deda: 25.3 seconds - Del Mondo: 25.5 seconds
So it's clear that the Criteriums are slower. Part of that is because they are so narrow (the 25 mm Michelins were 0.6 seconds faster than the 21 mm wide ones). Part of that is the "sew-up penalty." The Del Mondos were statistically the same speed as the Dedas, even though they are a lot wider. Again, there appears to be a slight "sewup penalty."
However, in tests on steel drums, the "sewup penalty" is much greater, because the improved comfort (less vibration of the bike) does not come into play.
So the fastest tire, in theory, would be a Campionato del Mondo clincher, but the difference clincher-tubular isn't all that great. Racers would do well to use 28 mm tubulars instead of 21-23 mm wide ones.
We also found that unlike the clinchers we tested, the sewups actually became slower when we inflated them very hard. The Criteriums were faster at 105 psi than at 130 psi. The Del Mondos were faster at 85 psi than at 105 psi. Of course, this depends a bit on the road surface - on very smooth roads or the track, higher pressures probably offer more of an advantage.
The biggest problem is that what feels fast and what is fast are two different things with tires. We associate higher frequencies of vibrations with faster - the faster you go, the quicker you hit the road irregularities.
However, using a narrower tire at higher pressures also gives you higher frequencies, and thus tricks you into feeling faster even if you aren't. This still works for me - whenever I ride narrow tires, I feel super-fast. Then I ask Mark, who is riding next to me on his usual 650B x 38 mm tires whether we are going faster than usual, and the answer always is "No." Tricked again!
Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com