Converting a Pedal Bike to an E-bike – My Experience

By Paul Levett. All images courtesy of Paul Levett.

I am a cyclist who rides for transportation. I got into e-bikes after ten years of riding the Metro and decided to commute by bicycle to work in downtown Washington, DC. I needed a pedal-assist to cycle uphill to my home in Arlington, VA.

In fall 2016, I bought a Bafang BBS01 (also known as an M215 or G340.250) mid-drive kit motor and 36v battery.

See also my article about Enviolo hubs.

Deciding on a pedal bicycle to convert

I wanted a step-through bike with an internal gear hub (IGH) to shift gears when stationary, with the ability to mount a mid-drive motor and carry the battery on the downtube to keep the weight low and central.

Frame type and assembly

The first-generation Breezer Downtown ST had the mid-step frame and internal geared hub I was looking for and the mid-step design meant I could mount a battery on the downtube. Breezer has since changed the design of the Downtown ST to a traditional loop frame step-through. This design requires a clamp designed to mount the battery vertically on the seat post such as the Lekkie Frame Clamp Set or Grin Tech Bottle Bob.

Papillon Cycles of Arlington placed the order and assembled the bike for me with some modifications: I had them remove the bottom bracket so I could fit the motor, and they replaced the 18t rear sprocket with a 21t so I could get the 2:1 ratio Shimano recommends for the Nexus IGH with the new 42t front chainring.

The width of the motor meant I had to replace the Breezer chainguard to fit an Hebie chainglider of the right size to work with the front chainring and the Shimano Nexus 8 IGH. It works well to keep my pants and the chain clean. I upgraded the bicycle touchpoints with Ergon grips, VP flat pedals, and a Brooks B66 sprung saddle.

Power, speed, and weight

Two questions remained: Could the bicycle gears handle the motor's torque and were the brakes capable of stopping a heavy bike?

To ensure the motor cuts out when shifting gears, I had Papillon Cycles fit a gear sensor in line with a new gear cable. This solution is more basic than Bosch's shift detection system, but it works to momentarily cut the power and ease up on the drivetrain. I also had Papillon Cycles replace the front rim brake with a Sturmey Archer 90mm drum brake that stops reliably in all weather.

Adding e-bike-specific components

In addition to the motor and battery, I added a throttle, display, wheel speed sensor, and torque arm on the chainstay to prevent the motor from rotating in the bottom bracket.

I installed e-brake sensors that stop the motor, and managed cables with spiral wrap, neoprene, and zip ties. An Anderson tap was installed in line with the battery wiring harness to power e-bike lights off the battery.

The BBS01 has 6v/3w light connectors but tapping the main battery power wire permits brighter lights. I upgraded from a 1.5w/100-lumen to a 5.5w/400-lumen headlight with a broader beam pattern that allows me to better see dog walkers and joggers at night.

Deciding on an e-bike kit

The simplest and least expensive e-bike kit to install is the Hill Topper Sprinter ($550), which replaces your front wheel, so you don't have to mess with the pedal bike's gearing. The drawback is that the conversion kit offers only a throttle and no pedal assist.

If you want pedal assist, the slightly more expensive hub kits from Ebikeling come with a clip-on cadence PAS sensor. My BBS01 uses both an internal cadence PAS sensor and a wheel speed/spoke magnet sensor. The BBS01 and a 13ah battery currently cost about $750 online.

I chose to fit a Bafang BBS01 mid-drive motor because it offered twice the torque (80nm) of an equivalent 36v hub motor to bike up hills. I weigh 240lb, the bike weighs 35lb plus another 20lb for the motor, battery, and drum brake. Sometimes I tow a trailer with a passenger. The result: The Bafang motor is capable of winching up to 365lb of weight on my rig uphill.

Other Bafang mid-drive models like the BBS02 and BBSHD have a wider stator to provide more torque, with upgraded controller mosfets that can handle the increased current without overheating and would be a better choice for a cargo bike. The BBS01 does what I need it to do.

Conclusion

Would I do it again? Yes, although I would be interested in trying either a 48v BBS02 motor or the TSDZ2 motor that uses a torque PAS sensor.

How is the bike performing? I highly recommend installing the gear sensor. I tried operator training to cut the power when shifting, but there is no substitute if you want to protect the drivetrain.

Was it cost-effective to build your own e-bike? Installing a Bafang mid-drive requires bottom bracket removal tools and an understanding of bicycle drivetrains. I recommend working with a local bike shop on the conversion as I did.

In return for their help, I became a regular customer, spending an average $200 each year over the past five years, paying for their expertise and shop tools to install/remove the kit and service/upgrade the mechanical bicycle components.

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