Comment Re:Real advantage is the assist, not the braking. (Score 1) 49
It's more than just a set RPM. It is also a set power level. An ICE engine is typically the most efficient at a set RPM and 70-80% of maximum power for that RPM.
Then size the engine for roughly highway speed on level terrain. Maybe give it the ability to go higher in RPM - less efficient, but able to handle going up a big hill/mountain if necessary. But ideally the battery would handle that, then charge up on the way down.