[dcb]

yes, a chain primary reduction sounds sort of harley-ish but on most of the exploded bike diagrams I've seen there is a small gear on the crank and a large gear on the clutch basket or something.

from there both cars and bikes suffer from constant mesh transmissions (for packaging) as opposed to some configuration that only meshes the gear in use.

then most every bike I have had takes the output to a chain to the wheel, and a car would use a shaft and hypoid differential (rwd) or a reduction gear differential (fwd)

Best numbers I've seen for a chain were %98.