Compass 35mm tire on 32mm rim.

Here is a fairly precises example of the role rim width plays. I have Schwalbe Kojaks (35mm) on some rims that measure 24mm outside width. I have the exact same tires on a different set of rims that measure 32mm outside width. The tires measure slightly under 32mm on the narrow rim and almost 38mm on the wide rim. Huge difference. Also, because of the added volume of the wide rim/tire combo, air pressure requirements are VERY different between the two sets. Even though the narrow rims weigh less, the wide rim set up feels faster, grippier, turns better, and handles bumps better. I think it's because the contact patch is wider and shorter, so less rolling resistance even with less PSI. Kinda like the best of both worlds.