How to install an electric motor on a bicycle

Written by chris keam
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How to install an electric motor on a bicycle
An electric assist is a great choice for parents who need some help to tow a child on a tag-along bike or bike trailer. (cycling, san francisco image by Greg Pickens from

Installing an electric-assist motor on a bicycle takes a couple of hours and can be done by anyone with a basic knowledge of bicycles and electronics. The most common electric-assist kits have a hub motor mounted either on a front or rear wheel, a battery and its accompanying rack, and a motor controller. Installation for the two systems is essentially the same.

Skill level:

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Things you need

  • Electric-assist conversion kit
  • Metric Allen keys
  • Metric box wrenches (or adjustable "crescent" wrenches)
  • Multi-bit screwdriver
  • Pliers
  • 6 to 12 zip ties
  • Tire levers (if necessary)
  • Tire pump (if necessary)

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  1. 1

    Remove the appropriate wheel (front or rear depending on your conversion kit) from your bike. Most wheels come complete and ready to go, but if the wheel for your conversion kit didn't come with a tire and tube, deflate the tube on your old wheel, and use the tire levers to remove the tire. Take the tire and tube and install them on the new electric-assist wheel.

  2. 2

    Install the electric-assist wheel on your bike. If your tire has a directional tread pattern, make sure the wheel is installed appropriately. Look for an arrow graphic on the sidewall to indicate the correct tread orientation. To reverse its direction, simply flip the wheel around so the tread points the right way. With the wheel in place, tighten the axle nuts to secure the wheel to the fork or rear drop outs.

  3. 3

    Install the battery pack. Some kits (for example, Bionx) come with a battery that attaches to the bike's down tube water bottle mount. Many use a bag strapped to the rear rack, while others have a dedicated rear rack with the battery sliding into a mounting slot either beneath the top deck of the rack or along the side. Your conversion kit will indicate which style you have purchased. If you need to install a rear rack to hold the battery, begin by loosely attaching the struts to the bottom of the frame (don't tighten the bolts all the way). Then attach the rack to the seat stays using either pre-drilled, threaded mounts on the seat stays or the brackets that are included with your rack. With all four bolts attached, make sure the rack is level by sliding the rack forward or backward along the mounting arms underneath the front of the rack. Tighten all the bolts to secure the rack in place.

  4. 4

    Attach the motor controller to the right-hand handlebar of your bike. Make sure it is inboard of your shifter and brake levers so that you can brake and shift gears safely. A thumb-operated throttle can usually be installed without taking off the grip. If you are installing a twist throttle, you may need to remove your handlebar grip. If it's necessary to remove the grip, twist it back and forth to work it off the handlebar. To speed up the process, lift the lip and squirt some WD-40 or isopropyl alcohol under the grip to make is slide more easily, but be sure to wipe the handlebar dry before remounting the grip. If you bike has "lock-on" grips, simply loosen the Allen keys that clamp the entire grip to the handlebar and slide it off. Position the controller and throttle so they are easy to reach and/or read. Tighten the clamping bolts holding the units in place.

  5. 5

    Attach the wiring harness terminals connecting the motor controller, battery and motor. Use the zip ties to secure the wires along the bike frame and make sure there is no slack in the harness that could interfere with braking or get caught in the spokes.

  6. 6

    Charge your battery. When it's fully charged, install it in the supplied rack or carrying bag. Double check your wheel to ensure the nuts securing the axle to the front fork or rear dropout are tightened. Make sure you have reattached the brake cables. Test your brakes, and in the case of a rear hub motor make sure your rear derailleur is shifting smoothly. Double check the wiring harness and ensure there are no loose wires or excess cable that could be caught in your wheels and chain or restrict the handlebars from turning.

  7. 7

    Test ride your new electric-assist bike. Practice braking and make sure your brakes are in good working order to handle the additional weight and increased speed. Start with short trips or have a backup plan in case you overestimate the range capabilities of the battery.

Tips and warnings

  • Rear hub motors are good for people who want to be able to remove their front wheel and lock it to the frame when they aren't riding.
  • Buy as much battery power as you can afford. You may choose a bigger battery or a second unit, but having additional power equals peace of mind and confidence that you won't have to rely on pedal power alone when you run out of juice.
  • If you need to recharge your battery at work, buy a second charger unit. They are one of the more delicate pieces of the electric-assist bike componentry and carrying it back and forth from home to work can damage it. They are also relatively heavy. You'll be happier if you don't have to lug a single unit back and forth from home to work.
  • There are a variety of restrictions and rules regarding electric-assist bikes. Europe, Asia, Australia, New Zealand, the United States and Canada have differing limits on power, top speed and motor controllers. Be sure your kit will be legal in your area. Most kits will specify the countries where they are street legal. Also check the rules regarding bike paths in your area. Some paths forbid motorised vehicles entirely, while others will allow bikes and scooters with electric-assist.

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