Electrify Your Ride: Page 2 of 4

Converting Your Bike to Electric

Inside this Article

Electric Bike Ride
The newly electrified bike goes for its first test drive—with success!
Rear-Wheel Hub Motor
A rear-wheel hub motor.
Outboard-Mount Currie Motor
An outboard-mount Currie motor and drive.
Dual 1,000 Watt Golden Hub Motors
Dual 1,000 Watt Golden hub motors give near-motor-scooter performance.
Lithium-Ion Battery Pack
A rack-mounted lithium-ion battery pack.
Thumb Speed Control
A thumb speed control.
Motor Speed Controller
A motor speed controller.
The E-BikeKit comes with the motor (the wheel shown in the box) and controller. The battery (the silver tube), charger, and rack came separately.
Electric Bike Ride
Rear-Wheel Hub Motor
Outboard-Mount Currie Motor
Dual 1,000 Watt Golden Hub Motors
Lithium-Ion Battery Pack
Thumb Speed Control
Motor Speed Controller

I bought a new bike specifically for my conversion, so there was a lot to choose from and no repairs or alterations were needed. Most electric bike shops are willing to talk about the process of electric conversion. East Coast Alpine, in Danvers, Massachusetts, helped us find a bike that would be a good fit. Many bike shops are beginning to add electric bikes to their product offerings, so it’s something they’re embracing. 

Motors. The most common type of bike conversion motor is the hub-integrated motor, built into the wheel—there’s no drive train to deal with and no radical modification of the frame required. Generally, you buy the motor and wheel as a prebuilt unit. They are built to accommodate the drive gears of your pedal-bike, and its braking system. You simply place the order and specify what size and type of wheel you need, and the motor/wheel comes complete. Installing it is simply a matter of mounting the tube and tire on your new wheel, and replacing the original wheel with the powered one. 

There are two basic types of integrated hub motors: geared, and direct drive. The geared motors are smaller and lighter, and they offer less resistance when you’re pedaling. The direct drive motors are bigger, and can be more powerful, but are heavy and have more pedaling resistance. If you’re going for a power-assist strategy, where the motor is there to help you out, the slightly more expensive geared motors are the way to go. If you’re looking for a high-powered ride that you’re probably not going to pedal much, one (or two) of the larger direct-drive motors will give your bike more of a motor-scooter/moped feel. 

There are some motors that ride “outboard” of the wheel, but they’re fading from the market. These also require a special wheel, with a separate drive gear for the motor on the bike hub, and are generally cheaper than a hub motor. They’re bulkier, not as powerful, and add weight on the left side of the bike, not the center. With the progress being made in hub-motor development, they’re not as attractive an option for a daily ride. 

Motors’ maximum speed is determined by the voltage—the higher the voltage, the faster the motor will spin. A 48-volt motor will have a higher top speed than a 36 V motor (typical voltages for electric bike kits), but a 48 V motor needs more battery cells to produce that speed. If you’re looking for a simple assist, 36 V is fine; if you’re looking for scooter-like performance, you’re going to want a 48 V kit. 

The second critical rating is the motor’s power capacity, rated in watts. This will tell you how much weight it can pull and give you a pretty good idea of top speed and acceleration. The smallest motors you’ll see on an electric bike are around 250 W, and will give you a gentle assist. More typically, you’ll see a 300 to 350 W motor. The biggest hub motors are in the 1,000 W (1 kW) range, giving them a performance more like a true moped or motor-scooter.

When making the motor choice, you can choose rear or front mount. Typically, you want to mount the motor on the rear wheel to maintain the balance of the bike. The only time you’d stray from that is if you’re running a very small motor, or your bike won’t accept a rear wheel replacement. For instance, some bikes are equipped with 3- or 5-speed rear hub gears. In that case, if you put in a rear hub motor, you’d lose your gearing.

Brakes can also be a complication. Most hub kits have options for wheel-caliper or disk brakes, but keep this in mind when you’re making your decision—make sure your brakes are compatible. Almost all hub motors will fit in the axle space on a standard frame (100 mm front, 135 mm rear).

Batteries. Batteries are the oomph behind the motor, possibly the single-most important factor in the bike’s performance and cost. Two basic choices are available—lead-acid (L-A) and lithium-ion (Li-ion), a term covering a range of lithium-based chemistry. For the L-A choice, sealed batteries are usually used—they don’t need maintenance and they won’t leak if mounted on their side or tipped over. They’re low-cost but heavy for the amount of energy they provide. NiMH (nickel metal-hydride) is a choice you may see on occasion.  Their weight-to-capacity ratio is somewhere between L-A and Li-ion; they were a common option a few years ago before Li-ion technology was readily available.

For the same capacity (rated in amp-hours, Ah), Li-ion battery technology is usually half the weight of a L-A battery—but they’re typically about twice the cost. Li batteries have greater longevity, so they won’t need to be replaced as often, and the lithium is not as toxic as lead, although a little more difficult to recycle. You’ll want a battery that provides 10+ Ah, no matter which type you choose.

When weight-saving is important, Li-ion is clearly the best choice if it fits your budget. The good news is that the system is completely “battery agnostic”—that is, you can switch battery types at any point without having to make major changes in the system or design. You can add more batteries, you can change battery type, you can even switch between several types of packs as easily as you can remove and replace the pack, as long as the voltage is the same—for most systems, either 36 V or 48 V. It’s not at all unusual for people to start off with L-A packs and then upgrade to Li-ion when it is time to replace the pack. 

Comments (3)

Mark Smith W4CHL's picture

Quick comment: in the interest of simplification, the author should not have linked "speed" of an ebike motor to battery pack voltage. Peak speed under power is regulated in many countries, and even some areas within a country. Across the US the federal law is the motor assist must kick out at 20mph and the motor may be no larger than 750w (~1hp) to maintain the unlicensed ebike status. Most older systems are 24v, newer are 36v or 48v. Some may be modified to run faster, but the limits are not battery voltage, but the controller electronics and the motor peak wattage/hp.

Michael Welch's picture

Thanks for the good info, Mark. Yes, the federal limit is held to 20 mph and 1 hp for commercially-made bikes. But if you make your own ebike, state laws kick in. Here in CA, for example, I can build an ebike from parts or kit, and have a 1,000 W motor, though I am still limited to a max speed of 20 mph from the power system.

Bob Hoboken's picture

Your article is spot on in many ways. I ordered the Chinese kit from "the bay" for around 750 shipped. It's a 1kw golden motors hub with 20ah LifePo4 battery. I got around 1 year use out of it before the battery management system (BMS) failed. The battery is just a bunch of cells wrapped up in duct tape. It does work well though when it runs. I am 300 lbs and can get average 25-30 mph. Would recommend TOP of the line tires and tubes though. I had a front blowout at 25 mph and the road rash wasn't pretty. Also, anything handling power (controller / bms) gets hot. Hang those out in the airstream for cooling. Braking is HUGE when you add all the weight and speed to your bike. I honestly don't feel much difference in wheel braking vs disc. In wet weather I'd go disc. I don't have the controller to give regen a try for braking. I don't recommend rear drive given my setup. Adding disc braking is next to impossible and it was a b!tch to get the freewheel cluster to spin after installation. Clearances were tough to obtain given the chain and frame in high gear. If I were to buy another kit from China, I'd go front wheel drive. I'm hoping top tire makers like Schwalbe realize the need for beefier e-bike tires and develop them. Past 25 mph, you really are asking for it if you have a blowout. A helmet is a definate must, gloves and even other padding case you go down.
All that said, I'd not steer away from e-bikes for a second. They are flat out FUN and I've used mine for short commutes to work on a regular basis. Passing up gas stations daily is a joy you simply have to experience for yourself. I plugged in at work after doing the math for my boss (kill a watt meter helps) how little juice my bike drank. My commute was free at that point. I tow my battery in a well built 2 seat kid trailer. Work stuff and stops by the store go into the trailer. Don't rely on a seat post mounted tote for your 20ah battery unless it's welded steel. My very well made aluminum tote broke inside of 3 months.
Final thoughts, I will probably graduate into a small motorcycle simply for the better tires and brakes. A 48-72v motorcycle will have all the speed / range I need to get to work and our company now has charging stations available so again, my commute will be free. I look forward to leaving gas for good !!

Show or Hide All Comments


You may login with either your assigned username or your e-mail address.
The password field is case sensitive.