Non-original parts and modifications for the motor and drivetrain: upgrades, community designs and conversions that Sinclair never offered.
Reproductions of original parts aren't listed here. They're on the page of the part they replace; for example, metal gearbox inserts are on Gearbox.
Modifications that let the motor drive the C5 faster than 15.5 mph, or that use a motor rated above 250 W, take it outside the UK electrically assisted pedal cycle rules. See The law.