Originally Posted by
79pmooney
Narrower tires require less material, so they are lighter. Same with narrower rims. Narrower also decreases frontal area, reducing wind resistance so when narrower time/'rim aero combinations are made, they will be faster than wide ones.
We shouldn't talk about tire width in isolation, though. All things being equal, a narrower tire might be more aero, but coupled with a wider rim and the smoother transition from tire to rim, might the wider tire have an aero advantage over a narrower tire? Not claiming one way or the other, just throwing it out there.