Originally Posted by
ThermionicScott
As much as
1-2 watts at a power level most of us don't ride at, when comparing cog sizes that are at the literal extremes of what is possible on a FG bike (I've never seen a fixed cog bigger than 24T). So it's correct to say that the difference is down in the noise, for all practical purposes.
Right, so again, saying there is no difference is incorrect.
OP didn't ask if a particular rider could feel the difference.
And then there's this:
As power output increases efficiency increases because frictional losses become a smaller part of total input power. Typical best-case efficiency of a drivetrain in the 200 – 300 watt range is 96-97.5%. Above 300 watts typical best-case efficiency is 97-98%.
So any differences in efficiency are actually greater for cyclists of more modest power output than they would be for stronger riders.