We can all remember the good old days of the 23 mm tire on the 19.5 mm wide rim… they weren’t all that long ago (most still run this or a 19.5/25 mm combo). A few years ago, they started making rims wider because tire widths were on the increase as evidence made it clear that a plusher ride was more important to speed than a skinny, rock-hard tire. I’ve been running 25 mm tires on 23 mm wide rims on my Trek 5200 for the better part of two seasons. At the same time, I’ve been running 26 mm tires on 25 mm wide rims on my Specialized Venge. The 25s develop a flat track on the center of the tire while the 26s (on the 25 mm rims) aren’t nearly as pronounced.

Now, what I’m about to get into could very well be simply be a difference in tires (Michelin Pro IV 25s vs. Spec. Turbo Pro 26s), but the 26s aren’t developing a flat track in the center of the tire like the 25s are. That got me to thinking, I wonder what would happen if I put 24s on the 23 mm rims? The thinking, of course, is that with less of a “lightbulb effect” from the tire to the rim, the wear of the tire might improve.

I’m about to find out.

Vs

The Trek with Michelin 25s on the left, Specialized Turbo Pro 24s in the middle and Specialized Turbo Pro 26s on the Venge at right. It’s quite plain to see how much more clearance just that one millimeter gives between the 24s and 25s on the Trek. I haven’t quite decided which is a better ride, but I’m liking the 24 Turbo Pros at 90 psi a little more than the Pro IV 25s. It’s not a huge improvement, of course, but the ride seems a little more supple.

Anyway, if the two photos above don’t illustrate enough how much better the profile is between the tire and rim, as the “lightbulb effect” goes, have a look at this one:

Now, an important question would be, do the aerodynamic characteristics of the tires even matter on a Trek 5200? Not at all. A 5200 is only slightly more aerodynamic, as bicycles go, than a brick. But, if there’s an improvement in tire wear (and a small advantage in feel), plus a little aero gain that wasn’t there with 25s? Well that will absolutely make this little experiment worth the exercise.

I’ll have more on this at a later date. So far I like it. A lot.