The drivetrain requires special attention. There's no sense
in spending hundreds, if not thousands, of dollars to save
a percentage or two on battery efficiency if you're going
to waste it all as heat going through the transmission.
There are three basic ways to transmit mechanical power
along the drivetrain to the wheels: chains, belts, and
shafts. My initial focus was particularly on chains, as my
motorcycle already uses a chain. In any case, the only
other possibility would be belts-- from what I understand,
shafts are to be avoided on motorcycles as they're heavy
and not as efficient. On cars, they're probably the only
way to go.
For an good breakdown of chains vs. belts vs. shafts,
click here. However, note that in real
world terms the comparison is probably incorrect when
it comes to efficiency. Chains are far more likely
than belts to suffer efficiency losses due to wear,
dirt, and grime.
Read my explanation of chain design and selection.