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.
This is what i hve in memory but i might have missed something. I might ckeck the latest tests and will confirm or add something later the week.
Ride well
Michael Schmid Oberammergau Germany Tel.: +49 8821 798790 Fax.:+49 8821 798791 mail: schmid@zunterer.com http://www.zunterer.com
-----Ursprüngliche Nachricht----- Von: classicrendezvous-bounces@bikelist.org [mailto:classicrendezvous-bounces@bikelist.org] Im Auftrag von Jan Heine Gesendet: Sonntag, 23. September 2007 19:00 An: haxixe@gmail.com; hersefan@comcast.net Cc: classicrendezvous@bikelist.org Betreff: Re: [CR]Wheels make you faster, not frames.
At 1:03 PM -0700 9/22/07, Kurt Sperry wrote:
>I mostly agree, but I'd add that the assumption that fat tires are
>aerodynamically "draggier" isn't a safe one to make. Aero can be
>maddeningly counterintuitive, even identical shapes are subject to
>scaling (Reynold's Number) issues. Remember lenticular front wheels?
>They sure didn't look aero. It wouldn't surprise me a bit if fat tires
>(the rim profile's interaction with the tire's will also come into
>play) were found to be more aero. The wheel is interacting with the
>rest of the bike and the rider aerodynamically in turbulent/chaotic
>ways that can't be visualized in terms of the usual streamlines in a
>free flow. But you can't really tell without empirical data to
>analyse. And good, valid, repeatable aero data of mixed flows is
>famously difficult to acquire.
I have been unable to find any firm data on whether a narrow tire is more aero or not. You'd think somebody would have tested this at some point... If they have, the results are kept secret!
The only data I have found is from Continental, reported is on cyclingnews.com. It seems that they used a rider with a power meter, and sent them out once with a narrow tire and once with a wider one. While they showed a small increase (5%) in power output with the wider tire at a speed of 50 km/h (31 mph), there are so many variables that you cannot say anything with certainty. You'd need a very rigorous statistical analysis to show that your data is due to tire width, and not due to changes in wind direction or something else. Here is the link
http://www.cyclingnews.com/
As it is reported, I consider the data meaningless. At the very least, I'd like to see two runs with the same tire, and see whether the power output was the same... And of course, at lower speeds, wind resistance is less important and rolling resistance becomes a greater factor in the overall picture.
Since the data was lacking, we included this test in our wind tunnel testing - see the report in the latest issue of Bicycle Quarterly (in the mail right now, if you haven't got your copy).
We tested a Vittoria Open CX 24.5 mm tire vs. a Grand Bois Cypres 31 mm front tire. Both have similar tread patterns. We tested this both with a front fender and without. While the measurements for the narrower tire were 0.9-1% less resistance than for the wider one, the results were not statistically significant - that is, the difference was smaller than the noise of these wind tunnel tests. (The noise was not because the wind tunnel is bad, but because the pedaling rider changes position slightly, etc.)
So basically, if narrower tires are more aero, the effect is minor - compare that to the effect of lowering your stem by 20 mm (5%). This also makes me wonder about the 5% power difference in the Continental data - we don't even get 5% difference in wind resistance, much less in power output!
Wider tires have lower rolling resistance - which we confirmed in our real-road tire resistance tests - and it appears that wider tires will be faster at most speeds cyclists use. How wide? We haven't figured out at which point the returns from wider tires diminish and finally decrease (I doubt a 4" wide tire would be faster than a 2" wide one). To test this, we'd need tires with the same casing, but different widths. The only ones we have tested were Michelin Pro2 Race in 20, 23 and 25 mm. There was a clear trend, with the 20 slower than the 23, which was slower than the 25.
Classic content: the bike we used in the wind tunnel was my 1973 Alex Singer.
Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com