>>1157947Efficiency differences between an Alfine 11 and a derailer drivetrain are approx. between 3 to 8% at 200W (efficiency of the IGH changes depending on the particular gear, 2 to 6% at 50W). A Speedhub performs a bit better in some gears and even exceeds derailer efficiency in some at lower power levels.
Now, 8% might sound like a lot, that's 16W at 200W (let's just assume the derailer is 100% efficient), but in terms of speed it's fuck all if you're not racing. Let's say that 200W go you up to 19.74mph (that's what bikecalc gives), even a 10% loss down to 180W is still going to get you 18.96mph. That's right, with an Alfine 11 in the worst case scenario you're giving up less than 1mph even with a belt drive.
https://etrike.wordpress.com/2015/09/06/internal-gear-hub-efficieny-compared-to-single-speed-and-derailleur/http://bikecalculator.com/ 