seems like most racers use modified cruisers without thinking of how much weight can really matter. my first bikes were heavy beasts, built more to survive the streets instead of the track, and weighed 75-80 pounds.
the last bike i built weighed 50lbs and was a lot faster, and easier to handle. too bad it never finished a race.
on it's first outing i led a coupla laps until my pedal fell off.
the next race i snapped a ring starting the bike in the morning.
then i threw away all my broken china motors and sold the rest, vowing never to build another modified china engine. i may build a bone stock 50cc just for the slower classes, but...
my next bike will be handmade and using a minarelli v1 moed motor to run in the mid range class, or unlimited, depending on how fast i can make it.
as far as pedaling goes, it ain't called motor bicycling for nothin'. pedaling helps you at yhe start, out of corners, and anytime you need a boost to get your engine up to speed. i ran a tall gear and pedaled my ass off in every race.
tire size is up to you. i usually ran 24's. mostly because i'm short. i built a bike with 16" moped wheels (equivalent to 20" bicycle wheels) and the bike kept up.with the 26'ers for the most part. long straights they were a little faster, but getting out of corners was awesome. smaller wheels accelerate faster but you need more power to keep them spinning at top speeds.
gearing is based on the bike and the track. you figure that out as you go along...