Originally Posted by
chaadster
Ah, I was thinking that the X20 used the Capreo hub design to fit a 9t cog.
Even if a 20"er has the same gearing as a 700c, in any given gear pedaled at the same RPM, 700c will travel a greater distance, so a 20er needs even more gear range than a 700c bike to keep up. Outside of one-off record attempt small wheelers, I've never seen a 20" with gearing to match a 700c's capability.
No, if the top gear is the same (expressed in either gear-inches or in development) then the speed at a given rpm will also be the same. E.g. my Bike Friday with 451mm wheels (20" outer tire diameter) has a top gear of 109 gear-inches using a 60t ring and 11t cog while my Cannondale road bike with 700c (622mm) wheels has almost the same top gear (110 gear-inches) using a 53t ring and 13t cog. I could certainly get even higher gearing for both bikes, but the current high gear is already only useful for downhill runs or when in a fast paceline since I'm not strong enough to spin that gear on flat ground. Ultimately the highest useful gear on a bike is determined by the legs of the rider, not the size of the bicycle wheels.