Components

Building or upgrading

Components cover both the parts that wear out and the kits that turn an ordinary bicycle into an electric one. Conversion is often the cheapest route to an e-bike, but it is the area where legality goes wrong most often.

The legal trap with conversion kits

A conversion kit is sold as a component, not a vehicle, so nothing stops a UK retailer listing one rated well above the legal limit. Fit a 1000W or 2000W kit and the bike stops being a bicycle in law: it becomes a motorcycle or moped requiring registration, tax, insurance, a licence and an approved helmet, and your cycle insurance will not cover it.

A kit is only road legal if the motor is rated at 250W continuous or less, assistance cuts out at 15.5mph, and the pedals still drive the bike. Anything with a full throttle needs type approval even at legal power.

Higher-power kits still have a place on private land or a project bike that will be registered properly. They just are not a road-legal upgrade, whatever the listing implies.

Batteries

Replacement batteries are the other big spend. Compare capacity in watt-hours rather than amp-hours, and check the protection board rating matches what the controller draws.

See our UK e-bike law guide before buying anything advertised on power alone.