16 CFR § 1512.2 - Definitions.
For the purposes of this part:
(a) Bicycle means:
(1) A two-wheeled vehicle having a rear drive wheel that is solely human-powered;
(2) A two- or three-wheeled vehicle with fully operable pedals and an electric motor of less than 750 watts (1 h.p.), whose maximum speed on a paved level surface, when powered solely by such a motor while ridden by an operator who weighs 170 pounds, is less than 20 mph.
(b) Sidewalk bicycle means a bicycle with a seat height of no more than 635 mm (25.0 in); the seat height is measured with the seat adjusted to its highest position. Recumbent bicycles are not included in this definition.
(c) Seat height means the dimension from the point on the seat surface intersected by the seat post center line (or the center of the seating area if no seat post exists) and the ground plane, as measured with the wheels aligned and in a plane normal to the ground plane.
(d) Track bicycle means a bicycle designed and intended for sale as a competitive velodrome machine having no brake levers or calipers, single crank-to-wheel ratio, and no free-wheeling feature between the rear wheel and the crank.
(e) One-of-a-kind bicycle means a bicycle that is uniquely constructed to the order of an individual consumer other than by assembly of stock or production parts.
(f) Normal riding position means that the rider is seated on the bicycle with both feet on the pedals and both hands on the handlegrips (and in a position that allows operation of handbrake levers if so equipped); the seat and handlebars may be adjusted to positions judged by the rider to be comfortable.
(g) Recumbent bicycle means a bicycle in which the rider sits in a reclined position with the feet extended forward to the pedals.