Best Electric Bike Conversion Kits UK 2026

A conversion kit is the cheapest way to get an electric bike, and the easiest way to end up riding something that is not legally a bicycle. Most kits sold in the UK are listed on power, and most of the powerful ones are not road legal. This guide covers how kits work, which type suits which bike, what a realistic budget looks like, and the checks that decide whether your finished bike is still a bicycle in law.

What Comes in an Electric Bike Conversion Kit

A complete kit usually contains:

A motor, either built into a replacement wheel (a hub motor) or mounted at the pedals (a mid-drive).
A controller, the box that sits between battery and motor and decides how much power to send.
A pedal assist sensor (PAS), which detects that you are pedalling and tells the controller to help.
A display for speed, battery level and assist level.
Brake levers with cut-off switches, which kill the motor the moment you brake.
A throttle, on many kits. This matters for legality, covered below.

The battery is often not included, even on kits that call themselves complete. Check the listing carefully, because a decent battery can cost as much as the kit itself.

Front Hub, Rear Hub or Mid-Drive

Front hub motor kits

The simplest to fit. You swap the front wheel for a motorised one, mount the battery and controller, and run the cables. Nothing on the drivetrain changes. They suit flat commutes and lighter riders, but the front wheel can spin on wet or loose climbs, and they put real force through the fork dropouts. Always fit the torque arm supplied, and avoid them on carbon forks or suspension forks with lightweight alloy dropouts.

Rear hub motor kits

Better traction and a more natural feel, because the push comes from behind as it does when you pedal. Fitting is more involved: the motorised wheel carries its own freewheel or cassette, so you need to match your gearing, and rear dropout widths vary more than front ones. The most common choice for hilly commutes.

Mid-drive conversion kits

The motor replaces your bottom bracket and drives the chain, so it works through your existing gears. That makes it the most efficient option on hills and the closest to a factory e-bike in feel. The trade-offs are price, a harder install that usually needs bottom bracket tools, and faster chain and cassette wear. Your frame needs a standard threaded bottom bracket for most kits to fit.

Friction drive kits

A small motor presses a roller against the tyre. Quick to fit and remove, but they slip in the wet, wear tyres quickly and suit only light, occasional use.

Is a Conversion Kit Road Legal in the UK?

Only if the finished bike meets the same rules as a factory e-bike. The legal term is EAPC (electrically assisted pedal cycle), and a converted bike qualifies only when:

The motor's continuous rated power is 250W or less. Peak figures do not count, but a continuous rating above 250W fails.
Assistance cuts out at 15.5mph (25km/h).
The pedals still drive the bike, and the motor only helps while you pedal.

Throttles are where most kits fall down. A twist or thumb throttle that moves the bike without pedalling needs vehicle type approval, even on a 250W motor. Kit sellers almost never have it. If you buy a kit with a throttle, the legal route is to leave the throttle disconnected.

Fit a 500W, 1000W or 2000W kit and the bike is legally a motorcycle or moped. It then needs registration, tax, insurance, a licence and a motorcycle helmet, and your cycle and home insurance will not cover it. These kits are sold openly because a kit is a component, not a vehicle, so nothing stops a retailer listing one. The 2000W rear hub kit in our catalogue is a clear example: a capable kit for private land or a properly registered project, but eight times the road limit.

Our UK e-bike law guide covers the rules in full, and every factory bike that passes all of them is in UK Road Legal (EAPC).

Will a Kit Fit Your Bike?

Frame material. Steel and aluminium frames are the safe choice. Avoid converting a carbon frame or fork, which is not designed for the clamping and torque loads involved.
Dropout width. Most hub kits fit 100mm front and 135mm rear quick-release dropouts. Thru-axle and Boost-width frames need a kit made for them.
Wheel size. Match the motor wheel to your bike: 26", 27.5", 700c or 29". Road bikes on 700c wheels with narrow tyres are harder to convert well, and a mid-drive often suits them better than a hub.
Brakes. Disc brakes cope far better with the extra weight and speed. If your bike has rim brakes, check the rotor mount on the hub and whether your brakes are up to the job.
Bottom bracket. For a mid-drive, check your bottom bracket type and shell width against the kit before ordering.

Mountain bikes and older steel hybrids with disc brakes are generally the easiest frames to convert. Full-suspension frames can work, but finding room for the battery is often the sticking point.

Choosing a Battery

Compare batteries by watt-hours (Wh), which is voltage multiplied by amp-hours. A 36V 10Ah pack is 360Wh. As a rough guide, a 250W setup uses somewhere between 10 and 20Wh per mile depending on hills, rider weight and assist level, so 360Wh is enough for a typical commute with room to spare.

Match the battery voltage to the motor and controller, and check the battery's discharge rating covers what the controller draws. Buy from a seller who can tell you which cells are inside and what protection is built in. Fire services in the UK have repeatedly warned about fires involving cheap conversion kit batteries and chargers, so use the charger made for that battery and never charge it unattended or overnight near an exit.

How Much Does It Cost?

A basic front hub kit starts at around £100 to £150 without a battery. A decent 250W hub kit with a battery and display is typically £250 to £500, and branded mid-drive systems run from £600 upwards. Add fitting at a bike shop if you are not doing it yourself.

Compare that with an entry-level road-legal e-bike at £800 to £1,200. A kit makes most sense when you already own a good steel or aluminium bike you enjoy riding. If your current bike is tired, the money is usually better spent on a complete e-bike, where the frame, brakes and wheels are designed for the weight from the start.

Fitting It Yourself

A front hub kit is a reasonable first project if you can change a wheel and route cables tidily. Allow an afternoon. Rear hub and mid-drive kits need more tools and more confidence with gearing and bottom brackets. Whoever fits it, the jobs that matter most are a properly fitted torque arm, brake cut-offs connected and tested, and cables secured well away from moving parts.

Conversion Kit Questions

Are electric bike conversion kits legal in the UK?

The kit itself is legal to buy. Whether the finished bike is legal to ride on roads depends on the 250W continuous limit, the 15.5mph cut-off and the pedals driving the bike, with no throttle unless it has type approval.

Front or rear hub: which is better?

Rear for most riders, because traction and handling are better on hills and in the wet. Front if you want the simplest install and ride mostly on the flat.

Can I convert a road bike?

Yes, but it is harder. Narrow tyres, rim brakes and lightweight frames are all compromises for the extra weight. A lightweight mid-drive or a small rear hub kit suits road bikes best, and a carbon road bike should not be converted at all.

Can I fit a more powerful kit and ride it off-road?

On private land with the landowner's permission, yes. Bridleways, public byways, canal towpaths and forestry trails are not private land, and a bike over the EAPC limits is treated as a motor vehicle there too.

Browse all e-bike components and conversion kits for motors, batteries and parts.