Originally Posted by
Wilfred Laurier
This is not true. 'Rolling resistance', the energy lost to tire casing flex as you ride, is less for wider tires, if comparing otherwise identical tires. At higher speeds aerodynamics will play a part, especially if your rim is too narrow compared to the tire. And for climbs, the additional weight will play a part, although if the tires have identical construction then this will be pretty minor.. But if tire construction is the same, wider tires have less rolling resistance.
I have seen the studies where this is true comparing 23 vs 25 and 28 though most seemed to find that while 28 had an advantage the difference in resistance between a 28 and 25 wasn't as great as the difference between 23 and 25 and was becoming a case of diminishing returns. I've yet to see one that claims a 32 or 35 has a smaller contact patch then a 23 or 28 and I suspect that's for a reason. I assume that once you get past a certain point the sidewall has to be stiffer tomaintain the shape of the larger casing and weight eliminates any advantage in any situation. Even for light tires the difference between 23 and 25 can be several ounces per tire.
Originally Posted by
Wilfred Laurier
Russ Roth If we assume the cross section of the tire is round such that the increase in width corresponds to an equal increase in height, changing from 2.125" to 1.25", the difference to the radius is 0.875", and a difference to diameter of 1.75", which is approx. 7% of a nominally 26" wheel. To get the same drive ratio you would need to increase the size of the chainring by 7%. 44 x 1.07 = 47, so an increase of three teeth, which would explain
Miele Man feeling the need to swap from 44 to 48.
Miele Man has not told us that his average speed went up when he changed tires, just that he was spinning out, and a smaller tire would definitely require an increase in cadence to achieve the same speed in the same gear.
Wouldn't have thought it would be that big a difference but it seems it might be.