I'll have to check with someone cleverer othan me about that one, I'm not quite convinced about the same total surface contact area on similar structure/pressure tyres of different widths. Were one to take that to it's logical conclusion, you'd be faster on a bald MTB tire than a sewup. If you are right, I shall be shaving the treads off Knoblies with a razor and using those, because wider and higher tires are awful useful for riding bikes down steps and through flowerbeds. I am saying thereby that a wide tire is a useful tool for a fast commuter.
What I will go along with though is that everything is a tradeoff. And that there are so many unknown variables and interactions that there are many solutions on the market, and many variations in build (less so now with the carbon stuff, they all look the same to me). Nick Bordo, Agen 47000 France
hersefan@comcast.net a écrit : Tires are getting wider because rolling resistance, all else equal, is lower for wider tires (assuming identical casing and pressure). Of course we run wide tires at lower pressures, but the inverse of this statement is that it is possible to have a wide tire at lower pressure deliver the same rolling resistance as a skinny tire at high pressure - but the comfort is much greater on the wide tire!
So again, why aren't all race bikes using wide tires? Because everthing is a trade-off. Wider tires are heavier and have greater wind resistance. And acceleration is most important for those in a race. So where the typical non-competitive rider is best on a 25mm to perhaps 30mm 700c, the racer may go a big narrower. But the 19mm and 20mm tires were just too silly - the weight and aero benefits even for many pro riders to not overcome the relatively high rolling resistance such a tire yields.
Now if the road is increadibly smooth, and the rider's speed is extreamly high, very narrow tires might become optimal. Its all a math problem. Folks just get tripped up because they often don't understand that rolling resistance is caused by the tire forming the contact patch, and that wide "short" (with wide tires)contact patches are easier to form that skinny long (with skinny tires) ones.
And finally, one must remember that while heavy wheels are difficult to accelerate, they carry more momentum and don't deaccelerate as easily. That is why for time trial events at steady high speeds, wheel weight is actually far less important than rolling resistance or tire pressure. I also never understood why heavy aero wheels caught on years ago because I didn't think about the physics correctly - its because for a relatively flat time trial situation, rotating weight is Both friend and foe - so it really doesn't matter much!
Mike Kone in Boulder CO
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