Originally Posted by
icedmocha
This may be a silly question, but why are no bicycles with cogs outside of the rear dropouts? I know carbon belt drives are a thing, and the frame has to have a break to use them. So why no cogs outside of the rear drop out?
Because then, instead of the hub rotating around a fixed axle, the axle has to rotate, which makes for a trickier dropout to support a bearing for that, which describes a typical "semi-floating" car or truck axle. Or, a fixed axle that is hollow and the driveshaft fits through it and transmits torque only, does not take bending loads; I just described a "full floating" truck axle. It can be done, just at greater cost.