There is no "typical bent" wheel size. I have 2 and 3 wheel bents with 20", 26", 27" and 700C drive wheels. The larger drive wheels work best in the one I have (el cheapo BikeExtras found at the curb in the trash). The one that will not work has a 3 X 8 rear drive and a gear changer that sticks out of the axle. IMHO, riding on a trainer is boring compared to riding on the street.