Originally Posted by Az B
Bicycle riders generally can output about 1/4 horsepower. (I know, everyone here can do more that that, but we're far better than average... stick with me and you'll see the point) Chain drives can be well over 98% efficient. Shaft drives are doing well to be 85% efficient.
So with only 1/4 horsepower, can you really afford to lose 12-15% of your output to an ineffecient drivetrain? People spend an enormous amount of time and money trying to overcome even 1% of other losses like rolling resistance and wind resistance, 12-15% is quite a bit if you put it in perspective.
And then there's weight. Shaft drives are heavy.
Az
In addition to all that, one is limited to an internally geared hub to have more than one gear. That adds all the friction loss, and weight,of the hub on top of all that!
I have seen shaft drive bikes, they are available in the US. Just do some more searching.