Just like regular bikes, electric bikes experienced a pandemic boom—and have become equally hard to find in stores. That’s why adding a motor to the bike you already have can often be easier than finding a new ebike. How do I know? Let me tell you.
My wife started bike commuting last spring to her job in Washington, DC. There was one big obstacle: Capitol Hill. Not legislation, but the actual, elevated land feature. It’s no Colorado mountain, but it is a challenge, especially when she’s hauling work gear on a swampy day.
I, a bike nerd, leapt at the chance to draft her into the ebike brigade. But my local shop had maxed out its waitlist months before. City, mountain, cargo, folding, it mattered not what kind—the shop might place one ebike order that summer, but no guarantees. The other options seemed to be trusting local secondhand sites, with their iffy photos and vague descriptions, or gambling on lesser-known but in-stock brands online.
Or, it turned out, I could just make an ebike.
I could replace a wheel or the bottom bracket of my wife’s mid-1990s Nishiki hybrid bike, run some cables with Velcro and zip ties, and attach a battery. True, it requires moderate research, light to medium wrenching, and variable fiddling. But if that sounds like a good trade to get some lithium-ion pedal power, here’s what to consider if you’re interested in adding DIY range or hill power to your bike.
Where should the motor go on your bike?
Ebike conversion kits come in three main kinds, which I’ll list from least to most complex:
- Front hub (shown above): This process entails swapping in a new front wheel with a motor in its center.
- Rear hub: You make a similar swap, but for your rear wheel (in addition to a new freewheel or cassette cogs).
- Mid-drive: You install a motor beneath your pedals (in your bike’s bottom bracket).
Each setup has its pros and cons (see the tables below). The more you know about your bike, and how hilly and far your typical ride will be, the easier your choice will be. The hard part is forecasting how much power and range you’ll want once you’re into ebiking, said Adam Ostlund, managing partner at Electrify Bike Co., an ebike seller and shop in Utah. Ostlund gets customers saying they haven’t ridden in 20 years, and that they only want to take weekend rides with their spouse—but a year later, they’ve hit 3,000 miles and want upgrades. “Once someone starts riding ebikes, they’re always going to want more. So we try to start them at ‘more,’ so they don’t regret it later,” he said.
Front hubs
| Pro | Con |
|---|---|
| Easiest install | Limited in power (500 watts or less recommended, especially with aluminum or carbon forks) |
| ”All-wheel drive” (when also pedaling) on flat roads | Torque arms advised for more than 250 watts, complicating flats and repairs |
| Lower cost than rear hubs or mid-drives | Trickier handling and balance for inexperienced bikers |
| More battery-placement options (using smaller batteries) | Less traction on steep hills and poor road conditions |
| Discreet look thanks to a smaller motor | Easier to overheat motor on hills or spin-outs |
Rear hubs
| Pro | Con |
|---|---|
| Easier install than mid-drives | Torque arms needed for higher wattages |
| Better weight balance for hills and rain | Larger motors make heavier bikes |
| Higher power ranges available | Drivetrain and wheel components may be cheaper quality than original bike items |
| Fits bikes with irregular bottom brackets | Changing tires becomes more inconvenient |
Mid-drive
| Pro | Con |
|---|---|
| Use your bike’s gears to shift between torque and speed | More intensive install with specialty tools (and sometimes frustrating bottom-bracket sizes) |
| Better weight distribution | Best to avoid shifting while motor engaged |
| More safe power configurations | Faster drivetrain wear |
| Better for mountain/trail/hill riding | Less clearance under bike |
Most DIY ebike enthusiasts prefer mid-drive motors. Mid-drive motors leverage your bike’s gears to alternate torque and speed, unlike the blunt push of motorized hubs. They’re generally safer for your bike’s frame, especially with newer bikes made of aluminum, carbon, or alloys instead of older, tougher steel. They make more efficient use of battery power, especially on hills. And mid-drive motors’ weight sits evenly in the middle of the frame, rather than at the front or back. If you’re planning to tackle hilly trails, off-road conditions, or long ranges, a mid-drive setup is definitely best.
But hub motors have their place. They start at lower prices than mid-drives. They’re notably easier to install than mid-drives, and they let you avoid dealing with installing a motor into your bottom bracket, which can be notoriously varied in kind and size. Hub motors are a decent choice for commuting on paved streets with light to medium hills, when you’ll be using your legs most or all of the way. Just make sure that you brace your bike frame properly.
How will you control the motor?
The answer depends on what kind of riding you do. Most kits offer three main ways to control how much power your bike’s motor supplies, and when: a throttle, a cadence sensor, or a torque sensor. Some bike kits offer both a throttle and a sensor, for your choice or combination.
A throttle is what it sounds like: a button, lever, or handlebar twist that lets the rider manually apply power with no need to pedal. Throttle riding is what you see delivery riders using in major cities. It uses a lot more power. It’s also a useful backup if the bike, or the rider, starts to fail during a ride.
A cadence sensor turns your motor on when you are pedaling and off when you stop, increasing its output the faster you pedal. It’s usually paired with a kind of shifter to choose the level of assist (you’ll see this on most shared city ebikes). It’s more hands-free than a throttle, but it can be a bit awkward in low-speed situations, such as when you’re starting from an intersection.
A torque sensor gives you more power when you’re pressing harder on your pedals, whether you’re climbing a hill or pushing for speed. Torque sensors feel the most natural—they push hard when you push hard—but require more work to install and maintain.
How much power and battery do you need?
Once you’ve chosen a kind of motor, you decide how much motor you want, and how much battery you want behind it. Motors have watt ratings, batteries have voltage and amp hours—it’s a dense thicket for a newcomer. Micah Toll, an engineer who writes at EbikeSchool.com and Electrek, helped me focus on what matters.
First lesson: Ebike motor ratings are mostly nonsense. Some countries cap ebike motors: 250 watts in much of Europe, 750 watts in much of the US. Not coincidentally, motor makers and sellers advertise a motor’s “continuous” power instead of peak rate. The more clear way to compare ebikes is to look at voltage and current (amperage) for hill-climbing and top-speed power, and to consider watt-hours for battery longevity.
You can tweak voltage and current with different battery controllers, gaining more speed, more hill power, or different assist levels. The power you need depends on a lot of factors, including your body weight, the bike’s weight, and your pedaling power. Bicycling magazine has a deep dive on how to understand ebike motors and power (presented by Bosch, which makes its own ebike motors). Generally, 24- and 36-volt setups are for casual riders who plan to pedal a good deal and don’t face lots of hills, Toll suggests, while 48 volts and above are useful for hills and no-pedal throttle riding.
I went (very) small for my wife’s roughly $650 ebike kit from Leeds: a 250-watt, front-hub motor, powered by a 24-volt battery with 5.2 amp-hours, roughly the size of a squared-off 16-ounce beverage can. But watt-hours (Wh) offer a better battery comparison than amp-hours (Ah) do. You get watt-hours by multiplying the battery’s voltage (in this case, 24) by its amp-hours (5.2), so for my wife’s kit, that works out to about 125 Wh. That means, technically, her fully charged battery can run her 250-watt motor at full power for about half an hour. It’s a useful comparison, but ebikes pull “full power” only during hill climbs and acceleration, so their batteries usually last much longer. On a paved-road commute, your legs can likely put in 100 to 200 watts of power on their own, so using a low-key kit like this is like having an on-demand tandem partner.
For such “assist” rides, 250 Wh is a better starting point these days, according to Toll. If you’re going to be riding your throttle most of the ride, 500 Wh (that is, a 48 V, 10 Ah setup) is your starting point. If you want something close to an electric moped experience—almost entirely throttle, 25 to 28 miles per hour—look at 750 Wh setups, while also double-checking your local laws. (Such a setup might not be legal.)
My wife’s ebike is working well. Because she can safely store her bike at work and at home, she removes her battery only about once a week for charging. She gets most of the exercise of biking but can push a button to get a faster start at intersections or tackle hills. It has made her more confident in biking around the city, which means the local bike shops still get some business in accessories, lights, and more.
Where should you buy a conversion kit?
There’s no one ebike kit that I—or anyone—can recommend for most riders and bikes (though the Bafang BBS02 is currently regarded as the Honda Civic of DIY ebike mid-drive motors). But Adam Ostlund, Micah Toll, and Karl Gesslein, ebike enthusiast and author at ElectricBike.com, all had one bit of buying advice: Never try to “save money” hunting for cheaper batteries. It’s usually disappointing—and sometimes dangerous.
Bike batteries usually consist of a series of 18650 cells that are connected to each other and a battery-management system and then packaged into various shapes. Reputable battery makers and ebike kit sellers use the best-quality cells from brand names like LG, Panasonic, and Samsung. Most discount brands use lesser cells from lesser-known makers that have diminished capacity, voltage, and longevity, and their controllers can be equally suspect. Buy from a dealer with an established presence and return policy.
You can often find the motors, batteries, controllers, wires, throttle, sensors, and other accessories you need sold separately, but unless you have a few conversions under your belt, you’re better off with an all-in-one kit. Kit makers have spent a lot of time testing how components work together, and they should be available for troubleshooting. Ostlund notes that Electrify Bike custom-programs some of its kit controllers, so riders aren’t stuck with the often aggressive acceleration curves of some motors that are meant more for delivery workers than for weekend warriors.
Ebike kit companies mentioned by the experts I talked to, linked in ebike enthusiast subreddits, and having generally built a good reputation include:
If you’re unsure about any aspect of your conversion, look for your bike model on the Endless Sphere forum or the /r/ebikes subreddit, or simply search the web for your bike name plus “ebike.” Bike owners who have stealthily converted their bike into an electric-powered dynamo love to tell people about it. Not that I’d know anything about that.
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