Originally Posted by
FBinNY
Speaking purely from a mechanical/speed/efficiency viewpoint, the 2% difference isn't that meaningful. But there's a hitch in that most (all?) IGH hubs are lose efficiency with load, so they'll be least efficient in hill climbing, when you need the most help. Some are also less or even least efficient in the lower gears compounding the problem.
But for general cruising around, you'd be very hard pressed to find a difference.
Do you mean they lose more absolute power under load, i.e. 2% of 350W is more then 2% of 200W? Or are you saying the efficiency actually gets worse with higher power?
A good approximations is that the loss in speed will be 1/3 the loss in power. So 2% loss in power translates to .67% loss in speed or not much as others have pointed out.
I would use an IGH with belt drive on my winter bike when they come up with a reliable IGH that can be shifted with normal road shifters. My impression is the only reliable hub is a Rohloff and for that you need to add some type of rotary shifter to the tops of your bars.