Posted by Gregory Maassen on March 18, 2021 - Latest revision April 30, 2021  Reading time: minutes remaining

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.

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.

Why convert a pedal bicycle to an e-bike vs. buy an e-bike?

  • You have a pedal bike you like that can accommodate a motor.
  • You want to use a smaller (lighter) or larger (longer range) battery from a different supplier.
  • You want to do some of your own troubleshooting, having assembled a kit with a multimeter to test electrical current and an understanding of your kit display's error codes.
  • You want to program the motor controller to meet your power needs. Adding an e-bike motor transforms the carrying capacity and range.
  • You can ride a heavy cargo bike, tow a trailer, or just climb the steep hills in the Washington, DC, area.

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 that does not work for conversion purposes.

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.

An image of a red Breezer Downtown ebike lovers

The motor and battery are mounted low and center.

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.

The Hebie chainglider for Shimano Nexus internal geared hub.

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.

The gear sensor cuts power when shifting.

The gear sensor cuts power when shifting.

Motor torque arm attached to chainstay

The motor torque arm is attached to chainstay.

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.

An E-bike front light e-bike lovers

The e-bike battery runs both lights.

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.

Some other technical details

Motor location: The Bafang mid-drives fit in a 68mm- or 73mm-wide bottom bracket.

Battery location and weight: I mounted the battery on the downtube water bottle cage bosses.

Chainring: Bafang mid-drives replace your front chainring, and the width can offset your chainline. This usually isn't a problem for an IGH but it can be an issue for derailleurs. I found the kit’s 46t chainring geared too high for my IGH, so I went down to a 42t chainring.

An adapter can accommodate chainrings of various sizes from 33t to 54t with a 110mm BCD (bolt circle diameter).

If you have a derailleur and find the motor width pushes your chainline out too far, there are dished chainrings by Lekkie that bring the chainline back up to 9mm.

Crank arms: After the poor-quality aluminum crank arms that came with the kit deformed on the motor's steel square taper spindle, I replaced them with a steel unicycle crankset.

E-brake levers: The kit e-brake levers made of stamped aluminum felt flimsy, cheap, and nasty. I replaced them with e-brake sensors that attach to higher-quality brake levers.

Pedal assist: Bafang mid-drives use a pedal cadence PAS sensor and a throttle. I use the throttle to get going, then pedal assist. Depending on the terrain, I ride at between 12-15mph, and uphill at an average of 8mph.

Power: Peak power is calculated by battery Volts x Controller Amps. Bafang mid-drives can be reprogrammed to change the current. I set the current to 18A on my 36v BBS01 so peak power is 648w, which doesn't overheat. My power/speed settings are programmed as a Class 2 e-bike.

Ease of programming: Some kits are locked down but Bafang mid-drive controllers can be programmed using a laptop cable and software. If you upgrade to an Egg-rider display, you can use Bluetooth to change the controller settings with a phone app.

Parts and service: I have had good parts support for my Bafang BBS01 mid-drive kit from California E-bike, and for other e-bike components from Grin Tech.

Legality of controller reprogramming: Changing the power and top speed, or adding a throttle, may change your e-bike's class, which affects where you can ride. Markel and Velosurance provide liability insurance for converted Class 1-3 e-bikes.

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.

Do you have an engineering background? Can anyone do this? I have no technical knowledge of bicycle maintenance or electrical engineering. The biggest expense isn't money, it's the time it takes to learn what works.

DIY-bike resources

Although many bike shops happily work on the mechanical bicycle parts, most will not troubleshoot or service your motor kit unless they sold it. I recommend that you buy from a reputable US or Canadian parts supplier with inventory, as supply chains are overwhelmed by demand.
An E-bike tool kit

E-bike kit tools.


Helpful tools

  • Crimp-on Anderson electrical connectors that I recommend instead of soldering.
  • A multimeter to test current at the electrical connections.
  • Marine liquid electrical tape and/or heat shrink wrap to waterproof connectors.
  • Zip ties, neoprene wrap, and Velcro for cable management.
Papillon Cycles in Arlington, VA, assisted with the building of my e-bike. They do not sell or service e-bike kits. ElectriCityBikes in Tenleytown, DC, do sell, install, and service e-bike kits.

I bought the Bafang mid-drive kit from California E-bike (currently they supply the more powerful BBS02 and BBSHD), as well as the torque arm, gear sensor, and e-brake sensors. I also purchased a Bafang installation tool to tighten the motor lock ring. The Anderson connectors, crimping tool, Anderson tap, and e-bike lights were purchased from Grin Tech.

Other resources I consulted included Reddit's e-bikes wiki list of suppliers, example builds on Electricbike.com, technical info on Endless Sphere, and YouTube videos from E-bike School and Grin Tech. I also reviewed e-bike conversion kits on ElectricBikeReview.com.

Paul Levett - E-Bike Lovers - Senior Contributor

Paul is a librarian, cyclist, and Dad, who emigrated to the US from the UK in 2005. He started riding a bicycle for transportation at age 10, delivering newspapers. Currently he rides a Breezer Downtown pedal bicycle converted to an e-bike with a BBS01 kit motor. Paul lives in Arlington, VA.


Favorite e-bike: Tern HSD


Paul Levett

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