On Jan 28, 10:27*pm, jeffreybike wrote:
Is there any real difference between 23mm and 25mm tires as far as
speed. Will 2mm make you that slower or faster?
thanks, Jeff

The first thing to realize is that tire sizes are nominal, not
actual. For many, many years tire manufacturers have mislabeled their
tires.

Why? Because many cyclists think any tiny difference will make
tremendous changes in their riding - especially differences in
weight. So Company X makes a 23 mm tire, but labels it a 25 mm tire.
And the deluded consumer looks in the catalog and says "Wow, Company X
makes a 25 that's fifteen whole grams lighter than that of Company
Y!" He buys it under false pretenses.

One of my riding buddies has always been very evenly matched with me.
In the past ten years, he's gradually gone to carbon fiber everything,
and his tires are now down to 19 mm that he says he inflates to 160
psi, to avoid pinch flats. I'm still on the same touring bike, riding
(actual measurement) 26 mm tires. He's still evenly matched with me.
It takes a big change in weight or rolling resistance to be
detectable.

Keep in mind, tires not only support your weight and give traction,
but they also provide suspension. Narrower tires are more like solid
rubber tires. A thin coating of solid rubber would have the lowest
rolling resistance on a perfectly smooth surface, but only track
racing takes place on perfectly smooth surfaces. On our roads, my
friends 19s are probably slower than my 26s.

- Frank Krygowski