Originally Posted by
lukewall
I commute on a 48x19 fixed gear rush hour with 700x23c wheels and 26" mountain bike with 1.2" slicks. I always feel like the fixed gear bike is by far the faster of the two even with the relatively low gearing. The fg feels faster when i get up to speed on open bike paths. The fg is a lot easier to maintain speed. When i get the mountain bike up to speed, even in the highest gear (42x11), i feel like i really have to work to keep it there. The only time the mountain bike feels faster is when i get to bomb down the bridges in nyc...the funnest part of my commute.
However, i never attributed this difference to geometry, weight, and aerodynamics. I would like to put 650x23c wheels on my fixed gear bike to see the difference in speed at different velocities.
Fair comment, but -- again -- don't see where/how these felt differences could come from wheel diameter per se. The only way to even begin to know would be to run multiple timed/heart rate monitored tests over a fixed loop multiple times, with:
1. Equalized gearing at a set cadence
2. Tire quality/tread (if any) design equivalent; ditto wheel quality
3. Same kind of riding position set up on two bikes (or switch wheelsets on one bike), re. rider's aerodynamic and pedalling efficiency
4. Rigid or suspension fork on both
and see what happens. Whenever this has been done, formally or informally, the usual result seems to be that wheel diameter per se has very little, if any, real effect. Many, many other factors do, but that's not one of them. The 'Porsche effect' is real, of course (60 mph feels way faster in a Porsche than in a BMW 7series), but that's a different thing.