I converted a cargo bike to an e-bike — here’s what I learned

The conversion is tedious but not difficult if you have the right tools. Just expect the unexpected.

For about seven years in my 20s, in the midst of a crisis of self, I abandoned my nerdy predilections and picked up a new hobby, cycling, which ultimately turned into a lifestyle.

During what I now think of as my time in the wilderness, I sold my giant game console collection (I have regrets), stopped buying computers, got rid of my car, and quit my data aggregation job to become a pedicab driver — a gig job before gig jobs were cool — and eventually a guide at a small bike tour and rental company.

One of my duties between tours was bike maintenance, and our mechanic taught me some neat tricks like wheel truing and how to build a bike up. I would never call myself a bike mechanic, but it did make me comfortable wrenching on the basics.

One day, a retiree who liked showing off his toys brought in a Copenhagen Wheel — a self-contained e-bike kit that puts the batteries and motor all in the rear hub of the wheel. When he let me ride it, the little bit of extra acceleration in each pedal stroke flipped a switch in my skeptical brain.

A few years went by, and I ended up with my own e-bike. They’re just so fun and convenient and may even fully or partially replace a car for some. They’re certainly easier to park, making e-bikes perfect for quick jaunts. And if the battery runs out, well, you’re still riding a (heavy) bicycle.

An electric cargo bike is an even better car replacement, but the good ones are so pricey that I never considered it. Never, that is, until an uncommon opportunity fell in my lap.

The build

A few weeks ago, a friend of mine who works for a nonprofit bike company in Chicago called Working Bikes offered me a 1,000W Bafang motor in exchange for my partner’s rarely used e-bike. I’d be able to convert the cargo bike she prefers to ride, and the shop would get something it could sell much easier. In my hubris, I thought this would be a two-hour job — boy, was that a deeply flawed assumption.

Last year, my partner bought a 2015 Xtracycle Edge Runner 24D cargo bike, the only brand anyone cared about in my hipster circle in the late aughts and early teens. It’s nice but not geared to be very fast, and the basic components that came with the bike needed replacing. Since it required work anyway, why not add a motor and electrify things?

Generally, there are two kinds of e-bike motors: mid-drive and rear-drive. Front-drive exists, with VanMoof (RIP) being one of the most high-profile proponents, but the vast majority of e-bikes use the former options. The Bafang motor I traded for is a mid-drive motor.

Despite some surprises along the way, the conversion went about as well as can be hoped for, given my level of experience. I mean, at the end, we have a functional electric cargo bike, so who’s complaining?

Image: Al2 / Wikimedia Commons (licensed under Creative Commons Attribution 3.0 Unported)

The biggest part of the conversion for most will be mounting the motor, and that’s pretty straightforward. I just needed to pull off the crank arms that hold the pedals, remove the front chainring, and pull out the bottom bracket (the hollow part where the crank arms attach). I used a couple of specialized tools to make this easy — a crank puller and a bottom bracket tool — along with an assortment of hexagonal wrenches.

Crank pullers are kind of neat, actually. They have two sections — an outer bit that threads into the outside of the crank where it attaches to the bike and an inner shaft, or spindle, that pushes in toward the bike as you spin the handle, pushing against the bike and pulling the crank off. Mechanical advantage!

After pulling the bottom bracket, I cleaned the old grease out of the shell, which is the part of the frame the bracket slots into. Once I’d done that, I could grease up and slide the motor’s bottom bracket shaft into the shell from the drive side of the bike, where the chain would be.

Securing the Bafang motor involves a small bracket, a locknut that requires a special wrench to tighten (the wrench usually comes with the conversion kit, but mine did not), and slipping an outer locknut over that. I didn’t tighten the inner locknut enough, which made the motor all floppy when I first test-rode the bike, so I had to go back and crank that down further.

Next, I needed to install the speed sensor, which uses a magnet attached to a spoke and a sensor fixed to the frame to give the motor’s controller the information it needs to determine speed (and the motor won’t stay engaged without it). This part was tricky since the elongated cargo framing is farther from the wheel than the seatstay of a normal bike, but I was able to find a spot that worked. Barely.

After getting the speed sensor in place, I ran into my first hitch of this project. The cable connecting the sensor to the handlebar-mounted display wasn’t long enough! I had to order an extension cable — this 60cm one did the trick, but that meant I had to wait for delivery to finish that part of the job.

But hey, that’s fine; I could still do some of the other work, such as swapping out the grips for the new ones (which included a twisting throttle) and putting on the display. This was easy enough — removing the old grips just required using a teeny tiny hexagonal wrench to loosen the minuscule bolts, keeping them snug, then slipping the new grips on, and the display simply clamps onto the handlebars and is secured with small bolts.

Then I hit another snag: the cargo bike’s existing shifter and brake were integrated. That meant I couldn’t reuse the shifter with the new brake lever included with my Bafang motor. Big deal, you say, why does it matter if you can’t replace the brake levers? Well, my e-bike motor uses the brake lever as a kill switch that stops the motor from driving the bike forward. Swapping the brake lever then meant I had to replace the shifter, too, and that’s a lot easier if I match it with a new rear derailleur and cassette, which needed to be changed anyway (more on that later).

Having not planned for this, I decided to simply move on to the next step and get the drivetrain back together so I could at least test-ride it. That’ll be easy! Or it would’ve been if the large tripod bike repair stand hadn’t tipped over, comically knocking everything near it to the floor, including the table on which I’d put the master link for my chain, sending the two-piece part flying.

Master links are cheap but small, and after something close to an hour and a half of trying to find the second piece, I gave up and went to my local bike shop to buy a replacement. (In retrospect, for this job, I didn’t need to break the chain at all.) By then, frustrated and exhausted, I decided to come back to the project the next morning.

The second day was easier. I replaced some cables and cable housing, put the chain back on, installed the cranks and a small chainring that came with the motor (more on that later) and took the bike for a spin. Everything seemed great! The motor was smooth and quiet, and the bike was fast. But there was a new problem — every time I goosed the bike hard, it made a worryingly loud popping sound.

I couldn’t figure out what was causing it. Maybe the kickstand, which was a little loose and drooping, was flopping against the ground? Was the motor still not tight enough and smacking the frame? When I made someone else ride it, I discovered that the derailleur’s idler pulley — the tiny set of cogs that hangs down from the rest of the assembly — was being yanked forward and popping back.

There are a few things that could cause this, but since I needed to replace the shifter anyway, I decided rather than chase that down, the best thing to do was replace the rest of the drivetrain, which I later paid a mechanic friend to do.

The battery ended up being another problem. See, I have no idea who makes it because the sticker on the side doesn’t list a manufacturer, the battery pack capacity, or if it’s been certified by a reputable safety lab. It’s a smallish black box that’s about three-quarters the width of a Nintendo GameCube and roughly the same height and depth. The bag it came with has velcro straps for attaching it to the frame, but they aren’t long enough to work on the Xtracycle, which has wider-set, beefier seat stays than a normal bike.

I managed to get the battery bag to stay in place, but look at those straps straining to do their job. This isn’t a permanent solution. Having a potential flamethrower from an unknown company (or e-bike-obsessed hobbyist) sitting under my butt isn’t great, either, so I’ll be replacing the battery soon.

The final item is the 30-tooth chainring I received with the motor; it’s a bit too small, and I want to swap it for something bigger soon. See, the rear cassette I had installed ranges from 11 teeth to 34 teeth — a nice spread, but combining it with the small chainring makes it feel very similar to the heavy-hauling gearing I had on my pedicab so long ago. That makes it less than ideal for transporting light loads quickly, usually a tiny human or some groceries. Adding a larger chainring to the bike will make pedaling at a higher top speed more comfortable, which is important now that it has the motor’s pedal assist pushing it along.

So the project is far from over, but I now have a techno cargo bike, and it works! The 1,000W motor has no trouble getting up to its roughly 30mph max in a hurry on throttle alone, and it’s quiet getting there. That’s a bit much for biking a kid around, though (not to mention technically illegal where I live), so I dropped the top speed down to 20mph in the controller’s settings.

Pedal assist feels good, too, at least at the lowest setting — any higher, and it takes over a little too much for my liking. As with my other e-bike, I don’t find myself using the throttle when I ride unless I want to get across a street quickly. The weak point in the system is definitely the battery, though — besides being unbranded and potentially unsafe, it’s small and drains relatively quickly.

It could still use some wired lights, a new saddle, and wider handlebars with space for extra gizmos and storage galore so that we’ll be that much closer to never, or almost never, needing to drive. Given that we’ve spent thousands of dollars keeping our two aging cars viable, that will be a dream fulfilled, indeed.

Lessons learned

Converting and upgrading a regular cargo bike into an e-bike left me with newfound respect for all the other DIYers upgrading their own bikes. I’m certainly no expert, and that’s the point of sharing — any regular Verge reader can do this and benefit from my successes and failures.

Would I do it again? Yeah, I would. It was fun. But if you do your own conversion, it has to be because you really want to and you know what you’re getting into. It might save you money, it might not — but the experience alone will be valuable.

In my case, the unexpected need for a new drivetrain and the labor to install it (my partner really wanted her bike back, and I didn’t have the opportunity, knowledge, or tools to do it in a timely manner) added more to the cost of conversion than I had hoped. And I still have to replace the battery and chain ring.

Still, slapping a motor onto a popular, long-running bike brand means I didn’t have to worry quite as much about the need for proprietary and costly parts (though cargo bikes certainly have their share of those). I recommend doing the same if you undertake your own conversion.

You can buy a kit with the same Bafang motor I used for under $500 — but throw in a battery, and you’re already looking at potentially doubling your cost. And if you find that you’re uncomfortable with doing the work yourself or, worse — screw something up — then you have to pay your local bike shop a steep (and well-earned) hourly rate to install it or fix your mistakes. By the time you tally up all the conversion costs, you’re inching into the same price territory as a good pre-built e-bike option from the likes of Yuba or Rad Power.

There’s also the E-BIKE Act to consider. If it passes, it would offer a 30 percent tax credit (up to $1,500) for e-bike purchases, making this kind of build for the dedicated few who just love a DIY project. Otherwise, a conversion might not be worth the effort if saving money is your primary motivator.

For me, the roughly 10 hours and about $350 (plus the value of the old e-bike we traded for the motor) I’ve committed so far to the conversion and component upgrades have been a worthwhile investment in the cargo bike and, importantly, myself. Now, when stuff breaks — and, inevitably, it will — I’ll likely be able to identify the failure and fix it, and there’s immense satisfaction in that.

All photography by Wes Davis / The Verge