Electric bicycles have been quietly taking the streets by storm in many parts of the world. Why? Because they’re a fantastically fun and efficient way to move around. You get all the joys and freedom of riding a bike (avoiding traffic congestion and parking, for instance) while smashing through physical limits on your ability to climb hills and cover great distances. Once you’ve got an electric bicycle it’s easy to leave the car parked in the driveway for all those short and medium-length errands. The e-bike will get you there faster, and with a 98% lower carbon footprint!
While there are many factory-made e-bikes these days, the movement was really pioneered and championed by a DIY maker community in the late 1990s and early 2000s who were electrifying their own bikes from scratch. You too can join in this phenomenon with just a spare afternoon.
In this project we’ll show how to convert your own bike into an electric-assist bike, using a basic front wheel hub motor kit. There are countless options on the market for front motors, rear motors, and mid-drive motors spanning all kinds of weights and power levels, but we’ll focus on a low-power front drive because it’s among the simplest to install and has the best chance of being compatible with any random bike in your garage.
- Bicycle Just about any bike you have lying around, whether it’s already a daily commuter or a vintage beater collecting dust in the garage. Old mountain bikes are usually ideal platforms, but almost any road bike, beach cruiser, or hybrid will work too.
One advantage of a front hub motor is that it doesn’t matter what kind of gears or drive chain you have. The only important detail is that the front fork has ordinary slotted dropouts (not a modern high-end thru-axle system).
- Hub motor conversion kit Many suppliers offer conversion kits that normally include the motor, battery, and all electronic controls needed to run the system. We’re using the G311 Front Minimal Ready-To-Roll kit from my company Grin Technologies. The kit includes a hub motor front wheel, battery pack, motor controller, torque arm, thumb lever throttle, and more.
- Disc rotor if your bike has disc brakes on the front wheel. The motors use a 6-bolt ISO disc that’s readily available from bike shops.
- Bottle-bob clamps to secure the battery, if your bike frame doesn’t have suitably located water bottle eyelets
- Display There are many options for handlebar displays if you want to view battery voltage, speed, and all that. But for this installation we’re going to keep it minimalist.
YOUR BASIC E-BIKE CONVERSION KIT
Hub motor wheel is small and lightweight (5lbs) and runs a totally silent helical gear system. It’s not a power machine for racing up hills, but it provides enough boost to transform your bike into something new while still feeling and handling like a normal bicycle and not a scooter. This motor is already laced into a 700c rim, common on road and hybrid bikes. Other sizes are available, including 26″ for older mountain bikes and 27.5″ for newer ones.
Battery pack We chose a 36V, 16.5Ah downtube battery pack because it’s light and still has decent range, about 35–40 miles on a charge. Larger batteries are available if you need to travel further, but they’re proportionally heavier and more expensive.
Motor controller The Baserunner motor controller in this system is built into the mounting cradle of the battery pack. On other kits the controller might be built into the motor, or supplied as a separate box.
Torque arm secures the motor axle to prevent it from spinning inside the frame. The motor itself has tabbed washers which do the job in many cases, but a proper torque arm provides extra security and is essential on weaker aluminum forks.
Throttle regulates the power you get from the motor. We’re using a thumb lever throttle since it’s most versatile, but there are also twist-grip throttles that act more like a motorcycle grip.
Spiral wrap and zip ties hold the motor extension cable and throttle wires snug against the frame and help the whole installation look neat.
INSTALL YOUR E-BIKE MOTOR
The following steps work the same for any ordinary bike. In this build, one of our new staff at Grin Technologies (hi Stuart!) had a used hybrid bike that he wanted to convert in order to speed up his commute.
You can watch a video of a similar kit installation first.
1. REMOVE THE FRONT WHEEL
The first step is to flip your bike upside down with it resting on the handlebars and remove the original front wheel, which will be either quick release or threaded with nuts. If you have rim brakes on the bike you’ll need to loosen the brake cable or deflate the tire to slide the wheel out from between the brake pads.
2. SWAP TIRE AND TUBE TO MOTOR WHEEL
Using the tire lever, or an improvised lever, carefully pry off the original tire from your front wheel being mindful not to mash the inner tube inside.
Once the tire and tube are off, install them on the hub motor wheel by reversing that process. Anyone who has fixed a flat tire will be familiar with this sequence, and it’s usually our baseline question on whether someone has the comfort level to install their own kit.
3. INSERT HUB MOTOR IN FORK
Here’s where things can get a bit challenging. The hub motor wheel should slide right into the fork dropouts if they have a 10mm opening, but sometimes the dropout slot isn’t quite wide enough. If that’s the case, use the hand file to enlarge the slot until the axle just fits.
Some kits use tabbed anti-rotation washers inside the dropouts to keep the axle from spinning; if these are used it’s important that they’re oriented with the tab pointing down. For this G311 kit, we’re replacing the tabbed washer with a torque arm plate that provides much better spinout resistance.
When you install the front motor, make sure the cable exit is rotated to point downward and the disc mount is on the left side of the fork.
4. INSTALL THE TORQUE ARM
The torque arm is designed to screw into the fender eyelet hole that is present on the majority of front forks. It’s held on with an M5 bolt, and a slotted channel allows it to adjust to different geometries and hole locations so that it lines up. For low-power motors like this, the torque arm isn’t always required but it’s a good safety measure to install one regardless, even with steel forks.
5. TIGHTEN NUTS AND ADJUST BRAKES
Make sure the motor axle nuts are quite tight, since there’s a lot of rotating torque on the axle. (We recommend at least 40Nm or 30ft-lb if you’re able to measure.) At this point, the motor is installed on the bike. You can inflate the tire and flip the bike right side up again so it’s resting on the wheels.
Now make sure your front brakes are working again. If you have rim brakes, you might need to adjust the pad position to account for the width of the new rim. If you have disk brakes and installed a disk rotor on the hub, then adjust the caliper left or right so that it spins without rubbing.
6. MOUNT THE BATTERY CRADLE
The battery pack fits on the down tube of the bicycle, where it locks into a cradle that’s held in place by the water bottle bolts. If your bike has mounting bosses (aka eyelets) for a water bottle cage that are in the right location then you’re set, just use the supplied low-profile bolts so the head doesn’t protrude.
If your bike doesn’t have water bottle eyelets or they’re located too far back for the battery to fit, then you need to use the bottle-bob clamps. These attach securely to your frame tubing with hose clamps and allow you to position the battery anywhere you like.
7. INSTALL THE HANDLEBAR THROTTLE
In order to fit the thumb throttle on the handlebars you first need to remove the grips and sometimes the brake lever too. These grips have Allen screws for cinching to the handlebars; simply loosen the screws and slide them right off.
The thumb throttle can be located on either the left or right side, and because it adds some extra width you may want to loosen and reposition the shifter and brake levers so that they can be reached comfortably without your hand feeling squished.
Slide the throttle into place and find a comfortable location for it and the brake lever and shifter, then tighten them up and slide the grip back on.
8. ROUTE THE CABLES
At this point, all the key hardware is on the bike and it’s just a matter of plugging the parts together and securing the cable run. Route the throttle cable to follow one of the brake or shifter cables, using the spiral wrap tubing. It comes forward from the handlebar and then loops down along the down tube to the throttle plug on the motor controller.
On the front hub motor there’s an extension cable harness that links the motor to the motor controller. This cable runs up the side of the fork, held in place with cable ties, and then follows the down tube to the matching plug on the motor controller. Use cable ties as needed and snip off the offending pieces.
9. PREFLIGHT CHECK
You’re ready to slide the battery into the cradle and go for a rip! But before running the system, always double-check these details:
- The motor axle nuts are done up nice and tight
- You’ve reattached your front brakes
- The front tire has been inflated
- The battery key lock is locked ON so that the pack won’t fall off when you hit a big bump.
With this done, you should be able to flip the battery’s on/off button to the On position, see the controller LED glow steady red, press the throttle, and watch your life about to be transformed as the youthful joy of riding a bike returns in glory. Grin away!
TAKE YOUR FIRST E-RIDE
Your newly converted e-bike will easily cruise at 20mph on flat ground. It will go up modest hills (3%–6% grade) fairly well, but will struggle on really steep hill climbs unless you supply a decent amount of leg power to the equation. That said, it’s still a lot easier than not having the motor.
The basic throttle control allows you to determine exactly how much power you want from the motor at any time. You can save the power just for hills and headwinds, or use it all the time to maintain a fast average speed. It’s also possible to add torque sensors or pedal sensors to the bike frame so that the motor engages automatically when you turn the cranks, but those usually require more specialized bike tools to install.
The range you can get from a given e-bike battery is no mystery, but it depends heavily on how it’s used. Most people with a bike setup like this will consume about 15Wh/mile. That means a 500 watt-hour battery would have a range of 500 / 15 = 33 miles. Going up hills you’ll need more like 30–40Wh/mi, while downhills consume nothing, and it averages out fairly consistent. If you don’t pedal at all, your average consumption would be more like 20–25Wh/mi, while if you use the motor more sparingly you can easily get down to 8–10Wh/mi and have great range up to 50+ miles.
If you’re purchasing a kit and want an estimate on how far it will go on a charge, it’s best not to compare the claimed range, but just look at the size of the battery in watt-hours.
Visit ebikes.ca and explore the Learn menu to find out why hub motors are awesome, the benefits of converting a bike over a factory e-bike, the history of the e-bike movement, and more. And jump into the e-bike community.
Got a different kind of bike or different needs? Watch a video overview of all the different e-bike conversions.