tire weight vs. "rolling resistance"

[rkoch]

I have recently installed Vittoria's open corsa evo cx tires on my bike. The are supposedly the stuff in terms of rolling efficiency, BUT the are 70 grams per tire heavier than my usual racing tire: Serfas seca comp, which are only 155 grams each. I have one ride in on the vittorias and have not noticed any difference in the ride, but I do notice the extra 140 grams when picking up my bike.

What are your thoughts on importance of rotating weight vs rolling resistance of/in a tire?

[mitre_tester]

[Danton]

Make sure you have the tyre pressure right. I don't know how much you weigh. Only if you are a "clydesdale" should you approach the maximum recommended pressure.

[djconnel]

A significant advantage in rolling resistance in tires is almost always more important than mass, for typical tires, unless there are additional considerations like handling. Consider: climbing a 10% grade with a slight (13 kph) tailwind at 1300 meters per hour so wind resistance is trivial. If a pair of tires is 200 grams heavier, that's an extra 0.71 watts. If the rider + bike = 75 kg, the difference in Crr to yield this same difference is 0.00027, 5.3% of a typical Crr of 0.5%. So even a 5.3% change in Crr justifies a 200 gram mass increase in the worst-case scenario of a very steep climb.

[GrahamB]

An important point is that you probably wouldn't notice a 10% change in Crr, but a stop-watch would. So if you are racing, DJC's answer is correct. However, you may have other priorities. Having a lighter bike than your buddies might be one of them, who's to say it shouldn't?






Actually lots of people will say it shouldn't, but that's a different issue

[djconnel]

Since I just dropped $2k+ on Nico's super-cool ultra-light wheels, motivated more by wonder for their lightness than by power-speed equations, I can't argue with that logic .

[rustychain]

Just to push the question, will going to 25's (heaver but reported lower Crr) be faster. Why do all the pros pick 22 or 23"s?

[ScienceIsCool]

The Crr will indeed be lower, but the frontal area increases a fair bit. The trade-off between rolling resistance and aerodynamic drag has an optimal point at ~23. I doubt there's be a noticeable or measurable difference by going to 25, but for heavier riders it may be more comfortable and deliver a better ride.

John Swanson

[djconnel]

The Crr will indeed be lower

Crr tends to be lower at the same tire pressure, but maximum tire pressure is higher on narrower tires. So depending on the tolerable tire pressure, the optimal tire width varies. A lot also depends on how stiff the sidewalls are. Fatter tires, I believe, tend to have stiffer sidewalls, which yield more resistance when they deform. Then there's also the issue of handling: fatter tires may not handle as crisply.

Wind resistance isn't necessarily higher on fatter tires: a lot depends on how the tire width is matched to the rim shape. There will be an optimal width which minimizes wind resistance for a given rim.