At 10:11 AM +0200 9/24/07, Schmid wrote:
>The german Tour bicycling mag did extensive testing on this subject. I
>remember the following conclusions:
>1. Tire width has no aerodynamic significance since most of the wind
>turbulances in a spoked wheel occur around the spokes.
>2. The contact area of any tire to the road at a given pressure is so
>small that tire patterns do not give any effect - so slicks or patterend
>tires act the same.
>3. Bigger and wider tires are more comfortable at a give pressure than
>skinny tires since they give more "suspension" due to their higher
>volume of air.
>4. Since skinny tire have smaller carcasses the power needed to work the
>tire is less than in wider tires. So they need in fact less energy.
>This effect can be compensated by using more pressure in a wider tire.
>
>The conclusio of the tests overall was that the myth really skinny tires
>(19mm) are faster then wider ones (23mm) is not true and their is no
>aerodynamic benefit. The other factors like weight, spoke count and
>rider position are more influentual than tire size - so to what you feel
>best with.
>
Tour's tests always are interesting. They make a greater effort than almost all other mainstream magazines to come up with useful data. If this really is what they wrote, then I am surprised...
1. This matches our data, but I am amazed they can say why the narrow tire is no more aero. In a wind tunnel, you can measure which setup has more or less or the same resistance, but not why... To figure out the why is very, very difficult. Smoke or a tuft wand can help you visualize the airflow, but at cycling speeds, this is not very effective.
2. I assume they talk about racing tires. We also have found that a fine file or similar tread does not appear to affect performance. Knobbies or thin ridges will squirm as the tire rolls and will affect performance.
3. That one is a tough one, too. Many believe that pressure alone matters, and that the comfort advantage of wider tires comes from allowing lower pressures. Since comfort is affected by so many other factors, and somewhat subjective, it's really hard to test this one.
4. That one makes little sense, as the thinner tire's carcass will deflect a lot more than the wider one's, and thus consume more energy. That has been established numerous times, and we found it in our tire tests as well. Perhaps they said that a _skinny_ tire needs more power because it deflects more, but that you can compensate by inflating the skinny tire harder. For really smooth roads, that should work. That is why indoor track riders pump their tires to 200 psi. Our tests have shown that the suspension losses on average road surfaces increase with high pressures and counter the decreased tire deflection.
However, the final conclusion is one that I can support. From our data, it appears that Eddy Merckx might have been even faster on 28 mm Silk Campionato del Mondos (or was the Paris-Roubaix back then the wider tire?), compared to the 21.5 mm wide "racing" tubulars he appears to have used most of the time. This would have gained more than the little holes drilled into his rear derailleur trying to save a gram or two.
Of course, the 'cannibal' won enough races as it was, and did not need to look for a technological advantage. He probably drilled the derailleur to make it look prettier, and focused on his training. His results show that he was right.
Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com