I have an old Renn 575 disc wheel, with 21mm outside rim width. I'm riding 23mm Conti GP4000S II tires, which bulge out beyond the width of the rim. I know that having the tire bulge out beyond rim width is slower and that'd I'd be faster with a wider wheel. I have decided that the increased rolling resistance of going to a narrower tire pumped to higher pressure is probably greater than what I'm losing in aerodynamic drag, but it's just a guess. I could also put a disc cover onto a lightweight rear wheel I recently built that has a 24mm outer width rim.
How much do I actually lose aerodynamically by having a wider tire than the disc? It's all in "dirty air" anyway, so maybe not that much? On the other hand, it creates the trailing edge of the whole bike/rider system, so it might make small eddies at the back that are significant?
How much do I actually lose aerodynamically by having a wider tire than the disc? It's all in "dirty air" anyway, so maybe not that much? On the other hand, it creates the trailing edge of the whole bike/rider system, so it might make small eddies at the back that are significant?