Can I legally buy/build and ride an ebike that’s faster than 20 mph? Yes you can, but you need to know that the ebike is no longer considered equivalent to a bicycle and is subject to other state vehicular classifications. The definitions for electric bikes spanning 20-30mph, and 1-2 horsepower ranges, will vary from state to state, resulting in a no-man’s-land consensus about limits for motor vehicle definition. The common label for a 20-30mph, 2-wheeled vehicle with active pedals is a Moped. Other MVA labels include motor scooter, motorbike and dirt bike which may have equivalent power and speed performance, but do not have pedals to assist and move the vehicle.
State laws tend to intermix the source of power as either gasoline ICE or electric drive. This is unfortunate because that neutralizes the environmental advantage of an ebike over an ICE moped. It also misrepresents the contrast in power output levels between an ICE and electric motor system. 50cc gas mopeds/scooters have a 2.5-4 HP rating, while the 20+ mph electric bikes will be 1-2hp, and ride much closer to a normal bicycle compared to a gas powered, 2.5hp moped. E-mopeds will weigh 55-70lbs. Gas mopeds and scooters are typically over 120lbs. E-mopeds are still electric bikes that get valuable power assist from human pedal effort and are usually much quieter.
The federal law will not prohibit a motor vehicle label and additional restrictions given by the state. States will typically define e-mopeds in the 1000W