Your 80% figure seems rather spurious, coming I think from extrapolating a gross simplification of some 2009 figures for much bigger motors. My vague understand

Your 80% figure seems rather spurious, coming I think from extrapolating a gross simplification of some 2009 figures for much bigger motors. My vague understanding is that smaller motors are hard to get as efficient. Some things I was looking at last year suggested things keep improving and that in excess of 90% was in theory quite attainable now for such motor sizes, though in practice you probably won’t find it on the market. But I did find components that should combine to something like 85–87%. (I don’t think I wrote my findings down, or if I did it was on a device I don’t have access to at present. But a quick search shows https://outriderusa.com/pages/electric-bike-efficiency https://outriderusa.com/pages/electric-bike-efficiency claiming a motor efficiency of 93%, which if paired with a generator of similar efficiency would yield 86.5%, assuming no transmission loss which is of course unreasonable, and assuming the efficiency stays the same at lower power levels, which is likely screamingly wrong.) >95% for chain systems assumes good components excellently-maintained. In practice chain drives are generally somewhat less efficient, commonly more like 85–90% is what I think I read, with poorly-maintained ones often more like 65–75%. This is where an electrical drivetrain could really shine: it’ll require roughly no maintenance while maintaining its not-best-in-class-but-still-pretty-good efficiency. These figures are all rather nebulous, and get muddied a lot further once you’re putting a battery into the mix too, trying to take the power from your feet and augment it with another 200W of power from a battery (but preferably without feeding your foot-power through the battery). Then I go from being an amateur that knows just enough to be dangerous to a rank ignoramus. For my purposes, an electric drivetrain would probably be markedly less efficient, but if it can be enough more convenient, it could be worthwhile anyway. I also have a pet scheme in mind where you simulate 100% efficiency by adding a little more power from the battery to compensate for known losses. I feel that could fit within the intent of legislation, if only that legislation allowed electric drivetrains in the first place.