Originally Posted by
Retro Grouch
So why do racers use such skinny little tires? Rolling resistance isn't everything. At roughly 15 miles per hour on a flat road, air resistance surpasses all of the other factors that are holding you back combined. As you r speed increases beyond 15 MPH, the importance of air resistance becomes progressively more and more significant. Skinny little tires have less frontal area and consequently less air resistance than wide ones.
It's not so simple as that. Air resistance is not just a function of frontal area, as turblence across the tire/rim interface and trailing edge of the rim can create a ton of drag. Being able to make light, wide, aero profile rims has changed the paradigm, and I'd bet the ranch that a 25c tire on a 22mm internal width rim with a 45mm deep profile has less drag than a 23c tire on a classic, 15mm internal width rim with a sub-20mm rim depth (e.g. the old Mavic Open Pro).
World Tour pro race teams usually run 25c these days (and wider on rough/cobbled segments), so they've come up in the past handful of years from 23s, but they're balancing weight and aero very carefully, so who knows if we'll see them on 30c in the future; I suppose it would depend on tire weight and rim weight for the width and depth needed to carry a 30c tire efficiently. Notably, Alaphilippe won TdF stage 2 last year on 26c S-Works Turbo rubber...on tubed, 33mm deep, 21mm internal clinchers at that, so yeah, width does not tell the whole story about aero.