Shortest possible route: 9 miles round-trip ... but who wants to take the short way?
Normal route: 21 miles round-trip
Longest route yet achieved: 25+ miles round-trip, but not in the winter.
Of course, they all get longer if I have to make other stops.

All of the routes are a mix of industrial neighborhoods, suburbia, and multi-use path (what 15mph speed limit?).

Average speed tends toward 16-17mph... it's pretty flat.