Originally Posted by rms13

Here is an interesting read:

THE RIGHT TYRE WIDTH ON THE RIGHT RIM WIDTH - Engineerstalk : Engineerstalk

Their tests show that 23mm tire on 25mm rim is more aero than 23mm tire on 19mm rim but 25mm tire on 25 rim is less aero than the 23mm tire on 19mm rim. They also found that tire width has a lot more influence on rolling resistance and comfort than rim width. You get 15% increase in air volume going from 23 to 25mm tire on 17mm rim and only 2.2% increase going from 17mm to 19mm rim with 25mm tire.

In the real world, I have ridden 23mm tires on narrow rims, 25-28mm on narrow rim, 23 and 25 on 25mm rim and 28-40mm on wider rim and I feel like 25-28mm tire gives me the best ride on road regardless of rim width