How to Convert a Road Bike to an Electric Bike

by tu2thepoo

43K18838

Intro: How to Convert a Road Bike to an Electric Bike

I converted my road bike to an electric commuter! I've been thinking about this project for a while, since I’m lucky to live close enough to consider bike commuting to work. On the other hand, hot summers combined with living at the bottom of a hill make it hard to get there without being drenched in sweat.

I found that adding an electric motor not only got me to work quicker (and drier), it made me more likely to use my bike rather than my gas-guzzling SUV or hailing a carshare. Your mileage will vary (pun!), but with my SUV's terrible city mileage and California gas prices, I figured this e-bike project would pay itself off within 2-3 years if it only cuts my driving in half.

That being said, being able to climb a hill at 15-18 mph while soaking up the sun has benefits all its own!

STEP 1: Decide If a Road Bike to E-bike Conversion Is Right for You

Like many DIY projects, this may NOT save you time or money if you're new to repairing and modifying bikes. Many folks will be better off getting a pre-built electric bike (e.g. from Luna Cycle or Propella, or Trek on the high end). I chose to do a conversion because I:

  1. Really wanted to keep my road bike and
  2. Already have a ton of tools from years of bike repairs and commuting to previous jobs.

Point #2 is often overlooked by new DIYers - you might not realize you need a specific tool until you've halfway disassembled your ride! And besides the general repair stuff (see Supplies), for this project you may need stuff to help you bodge things together in ways they weren't designed (JB weld, silicone sealant, electrical/duct tape, etc).

See below for videos for the general repair skills you should have as a baseline:

If any of the above look particularly daunting, you may want to reconsider converting your road bike.

If you're thinking "Sounds good! When do we get started?", let me point you at a quick primer on electric bike conversions, and the difference in motor types. Generally speaking, a mid-drive conversion like this project will have higher costs and maintenance requirements, in exchange for potentially higher performance.

STEP 2: Pick a Bike

This is what I started with - a Motobecane Vent Noir, which is a solid entry-level road bike. I’ve upgraded it over the years with nicer wheels, tires, a new seat, and all sorts of colorful accessories. Point being, if you've got a bike that already rides well and you know inside and out, you're probably in good shape.

On the other hand, if you're in the market for second-hand bikes, steel frame models are generally sturdy and cheap(er). However, you run the risk of having rust hidden in the frame, and spending the money you save up-front on replacement parts, later. Most newer road bikes are made with aluminum frames - there's a school of thought that aluminum is more likely to fail without warning, but this seems to depend on the abuse the bike receives.

On that note, if you’re really unlucky, the bike may be old/unique enough that you need single-purpose tools to get it ready (like a bottom bracket removal tool, chain breaker, or replacement hub bearings). If you can’t budget extra for ordering emergency parts and tools on short notice, you’re going to have a bad time.

These bike features will increase your chance of success:

  1. A large front triangle will give more room for mounting the battery.
  2. Water bottle mounts allow you to position the battery lower on the frame, which can improve handling. However, there are alternatives.
  3. A standard width/type bottom bracket will make mounting the motor easier.
  4. Wider forks/dropouts will generally let you mount larger tires, which will give you a more comfortable ride.
  5. Easily accessed shift/brake cables will make it easier to install sensors and adjust things during installation.

STEP 3: Choose a Motor, Battery, and a Vendor

I ordered the Luna Cycle Bafang BBS02 kit, since Bafang motors are very popular and there's a wealth of information and parts available. There are two models to consider:

  • The BBS02 only fits a specific width of bottom bracket without modification (68-73 mm). It is the lighter and more affordable option.
  • The BBSHD can fit a wider variety of bikes, and is built for long-distance/high-power riding without overheating. If you need your motor to power a half-century ride, the BBSHD might be the better choice. On the other hand, it's heavier, larger, and more expensive.

You can find more commentary here.

When it comes to batteries, you're looking at 36v, 48v, or 52v - all things being equal, a higher-voltage battery will be larger and heavier but last longer. The Internet consensus seems to be that 36v batteries are best suited for flat terrain and light duty, while 52v is overkill unless you're climbing huge hills - I went with 48v.

I chose Luna Cycle because their parts have an excellent reputation in the DIY community. I thought it was worth it to buy from a local vendor (they're based out of California!) who support their products and provide a ton of reliable information. They also source brand-name lithium-ion cells and make it easy to add on smart chargers (which can help extend your battery's usable life), suspension seatposts, and other useful accessories.

(As an aside, the smart charger has a high-pitched whine that comes from the cooling fan. I turned up the recording gain while recording the video, so keep in mind that the actual volume is a bit less.)

If you're comfortable navigating the AliExpress or Amazon marketplaces, the motor parts all come from China (where Bafang is based) and the batteries all come from Japan/Korea (Panasonic/Samsung) anyway. However, beware vendors with inaccurate listings, and counterfeit or under-specced battery packs.

STEP 4: Remove the Bottom Bracket

I followed an excellent youtube tutorial series from RevBikes: 1) Installing a Bafang mid-mount motor and 2) Bafang mid-mount: Installing the Bafang mid-mount controls

I’ll be providing timestamps when possible (removing the bottom bracket starts at 0:34 on video 1). If your bottom bracket doesn't match the video, refer to Park Tools’ comprehensive tutorial.

Try to clean the inside of the bracket slot (Fabuloso works well and is dirt cheap), but don’t worry about getting it sparkly-clean. Bafang motors only use the bottom bracket for structural support.

STEP 5: Fit the Chainring to the Motor

Mid-drive motors like the BBS02 use the existing drivetrain and augment your bike pedaling with electric power. They achieve this by spinning the front chainring directly, which then drives the chain and rear gears, spinning the rear wheel and moving you forward. From the bike's perspective, it's no different than having someone that can pedal many times faster and with much more power.


Without going into a huge amount of detail, the size of the chainring determines how much torque (rotation power) you get from a specific RPM (rotation rate). A smaller chainring will allow you to accelerate from a stop more quickly and will put less strain on your motor, but will have a lower top speed. A larger chainring will give you a higher top speed, but the motor will work harder to achieve that (which translates into more heat and battery drain). For guidance, I've broken the sizes (measured in the number of gear "teeth") into three general categories:

  • Small (30T) chainrings work best for riders who are regularly climbing huge hills (mountain bikers)
  • Medium (40-44T) chainrings are suited for riders who ride a mix of terrain and are not racing downhill
  • Large (48-52T) chainrings work best for flat terrain and riders who want maximum top speed

The Bafang kit comes with anywhere from a 44-52T chainring, depending on availability. You also have aftermarket options like the Lekkie Bling Ring and other "narrow-wide" chainrings. The major advantage with these is chain retention - that is, they reduce the risk of the chain flying off the gears. More discussion in a later step.

Follow along around 4:12 in the video for tips on how to fit the chainring to the motor. For reference, the default Bafang ring should "dish" inward, towards the motor (see picture). Definitely test how the ring fits before tightening any bolts.

One of the only complaints I have about the Luna Cycle kit is that the included bolts were too large. You can see in the picture above (and this video) that the ring actually rattles, and the bolts are long enough to scrape the motor housing if used. I solved this by purchasing some Origin8 Single-Ring Chainring Bolts (full disclosure: I didn't email Luna Cycle for replacements as buying the new bolts was quicker). You can see in the final picture that the new bolts fit just fine.

STEP 6: Fit the Gearsensor (optional)

The Gearsensor is an optional piece of kit that acts as an automatic clutch - it cuts power while you shift to avoid damaging the drivetrain. It's useful if you are keeping a 9/10/11-speed cassette on your bike, since 11-speed cassettes/chains are generally more fragile than 8 or 9-speed setups. Pedaling backwards will also cut the power from the Bafang motor, if you don't want to front $50 for the Gearsensor.

Note that I did NOT place the Gearsensor in the recommended position - it's supposed to be placed closer to the handlebar to avoid getting gummed up with mud and street gunk. We don't get too much rain in my town, so I felt safe mounting it on the downtube. I also wanted to avoid cutting up too much of my shift cable housing.

In any case, if you plan to use a Gearsensor, you should fit it on your bike prior to mounting the motor or running any other cables. I mounted mine with duct tape initially, and secured it with marine silicone sealant once I was sure it worked correctly.

On a side note, I had ordered two Gearsensors with the intention of using the second as a makeshift brake sensor (the regular brake sensor won't fit on a Shimano 105 "brifter" without a bit of improvisation). I had watched this video which claimed it was possible, but the Gearsensor I ordered won't physically fit a properly-sized brake cable. You can see the size comparison above (shift cable on the left, brake cable on the right).

STEP 7: Remove the Front Shift Cable (required) and Front Derailleur (optional)

Since the Bafang motor takes the place of your front groupset, you can (and should) remove the shift cable completely. The front brake cable should be left in place, and you can simply clip the remaining shift cable housing rather than re-doing your handlebar tape (although if you want to replace your bar tape, Park Tool has an excellent tutorial).
You can elect to leave the derailleur in place to act as a makeshift chain guide, but I chose to remove it to free up space for mounting things to my bike frame. I didn't have a convenient screw to loosen as in the Revbikes video, so I had to open the chain. With most 10 and 11-speed chains, there should be a powerlink that's easy(ish) to open, so I anticipated maybe a five-minute job.

Imagine my horror when I realized I had apparently run out of the single-use Powerlinks and forced an old-school bolt into the chain at some point in the past. There's nothing to do at that point but use the corresponding old-school chainbreaker and buy a proper replacement Powerlink. Off-brand versions are available on Amazon if the retail Shimano/SRAM prices are too much to stomach.

STEP 8: Check How the Motor Fits Before Bolting in Place

Mid-drive motors use the bottom bracket as an anchor point, and the Bafang motor can rotate slightly if needed. This allows you to fit the motor without pinching any cables or blocking any components. After you've removed the bottom bracket (as per Step 4), push the motor housing into the bracket as pictured above (if needed, you can use some grease and a soft mallet). This part of the tutorial starts about 7:30 into the Revbikes video.

Once in place, check to see if there's any welded components that potentially need to be sawed off, any cable guides that need to be clipped, or any shift cables that will rub against the motor. In my case, you can see that the cable guide cleared the motor (1st red circle), but the rear shift cable would be pinched (2nd red circle). I cut and taped together some spare bits of cable housing to use as a spacer.

Keep in mind that my bike is flipped over for these pictures, so when riding the mass of the motor will actually be resting on the mounting bolts. So you don't need to over-engineer whatever you end up using - in fact, mine fell off after a few weeks of riding without any issues. If you mount the bolts and retaining rings properly, the spacer is superfluous.

Finally, if a part of the frame is blocking the motor, remove it and try fitting again. If you're certain a frame component needs to be removed, you may want to check with your local bike shop (LBS) before doing anything. An errant cut with a hacksaw may compromise your frame's strength.

STEP 9: Mount the Motor and Test the Pedals

Now that we've sorted out fit and spacing, we can mount the motor with the bolts and retaining pieces. Make sure everything is facing the right direction (see pictures) and use Loctite on the threads if possible. The Revbikes video goes into more detail at around 11:25.

Once everything's bolted in place, you'll want to mount the crank arms and test the pedals. Loctite needs to cure for about 24 hours, so depending on when you started this might be a good stopping point for the day.

STEP 10: Replace the Chain and Check Shifting

With the motor mounted, it's time to place the chain on the chainring. "Narrow-wide" chainrings are usually recommended for single-ring setups, since they hold on better by virtue of the teeth matching the chain spacing (as in the picture above).

Once the chain is placed, you should check the shifting and adjust as per the excellent Park Tools tutorial.

Finally, you should take note of your bike's chainline after mounting the electric motor. As you can see on my 11-speed, wide-range cassette, the highest gear creates the straightest chainline (green), while the lowest gear has the most twist/worst chainline (red). The current gear is somewhere in-between (yellow).

This matters since running at low gear will stress the gear cassette and chain, but running at high gear will burn out the motor if you're attacking multiple hills each day. So make sure you downshift when you’re stopping, and shift to higher gears when you regain speed.

STEP 11: Connect and Route the Wiring

Luna Cycle sells batteries that can be used with multiple brands of motors, so the connector the battery comes with probably won't match the connectors on the Bafang motor (red circle, third picture). You'll need to either solder the connections or use a crimp - I went with the crimp, as a high-quality soldering iron can easily run you $100 (and requires an entire skillset of its own to use properly). I followed the crimping tutorial on electricbike.com and my bike works perfectly fine.

When you're first routing the wiring through the bike frame, I highly recommend starting with velcro zip-ties (see yellow circles on the third picture), rather than regular zip-ties or gluing. Each wire needs appropriate strain relief and can't rub on anything (red circle, 2nd picture), so you'll likely be changing things around several times before finding a good arrangement.

STEP 12: Install the Speed Sensor and Connect the Motor Controller

The speed sensor isn't strictly required for the motor to work, but it does enable the speedometer readout on the controller screen. I've also noticed that the motor will cut out or "hesitate" for a second or two if the speed sensor isn't reading, which is probably a safety feature.

I think the plastic bit that holds the sensor is designed for mountain bikes with wider dropouts than most road bikes, so it's difficult to mount in a convenient spot. The main factor seems to be distance, so the magnet and sensor don't have to be perfectly aligned as long as they're close together.

I ended up zip-tieing and taping the sensor in place temporarily - once I found a good position, I fixed it in place with silicone marine sealant. I also somehow lost the retaining bolt for the spoke magnet, so I used a machine screw to hold it in place. It's apparently pretty common to lose the spoke magnet, so keep in mind that any magnet will do if it's mounted/glued close enough to the sensor.

The relevant portion of the tutorial video starts around 16:54.

STEP 13: Take Care of Miscelleanous Items

At this point, it's time to consider the odd bits that you may need to modify to get everything mounted. Please refer to the 3x3 picture above.

Top row: the BBS02 control unit and throttle are built for flat bars (mountain/hybrid bikes) and won’t fit on drop bars (road bikes). I zip-tied the controller in place and decided not to use the throttle, which works perfectly fine. Finally, be careful how you route cables and try to use the existing holes in the frame to your advantage.

Middle row: I cut some cables too short and had to use my spare Jagwire brake/gear cables and my Pedros cable grabber to fix everything up. That can be an easy $70 expense if you don't have spare parts. The Cane Creek Thudbuster seatpost comes highly recommended for bikes that lack suspension. I bought the short-travel ("ST") version, which really absorbs bumps from poorly-paved city streets.

Bottom row: AZIZ, LIGHT! I’m a huge proponent of riding while lit up like a Christmas tree. Other drivers and bikers will NOT notice you even in the best of conditions, and you don’t want to be cut off going 20-25 mph on an aluminum death trap. I put together a double-barreled front light using a headlamp and a smaller bike light - it's a lifesaver for riding at night. You can find purpose-made lights but I didn’t want to deal with wiring them to the battery.

STEP 14: Consider Your Bike Security (AKA "Buy a New Lock!")

Let’s talk security. With all the cables and connections snaking around the bike frame, it’ll be pretty obvious to a thief that this is an expensive piece of kit. My current city doesn’t have nearly the theft problem that San Francisco/New York do, but you should still consider the SF bike coalition’s excellent advice for securing your bike.

I have a few U-locks (one Kryptonite New York Standard and a few cheap Bulldogs) and a chain - I use a mix of each depending on how long I expect to leave my bike alone. There are several comprehensive lock reviews online, but the general rule of thumb is to lock up with 10% of the cost of the overall bike - if your bike is worth $1500 to you, then buy $150-worth of quality locks.

On a side note, the Shark battery pack has a key lock which will be fine for a quick Starbucks run, but you’ll want to remove the battery if you’re parking for work or at a friend’s place.

Finally, consider your neighborhood - if your bike looks marginally harder to steal than the beach cruiser with a braided cable lock or the bikeshare sitting next to it, most thieves will go for those instead. You don’t have to be faster than the bear, just faster than the person next to you.

STEP 15: Tidy Everything Up and Do Final Checks

Before going on a ride, check for any snagged cables or pieces rubbing together. A bike tire spinning at who-knows how-many RPM will grind through insulation real quick. It’s one thing if it happens to your bike lock, another if its a high-current power cable.

Also, this is a good time to check if your wheels are spinning true. Any wobble in your ride will be magnified when you dial up the power on the electric motor.

If everything looks good, power on the bike and let 'er rip!


Closing Shoutouts:

Thanks for reading! Let me know if this Instructable helps you build your own road e-bike!

25 Comments

SCHLEPIC 4 years ago

Great documentation. Well done!

tu2thepoo 4 years ago

Oh cool! It may need a bit of tweaking since it probably won't fit a drop bar (same issue I had with the throttle control), but definitely a cheaper alternative to the gearsensor.

kiwironnie 4 years ago

Great project, well done.
There isn't a great deal of advice around on converting road bikes. So your write-up should be helpful to many.
The crank drive is great but more complex and risky to get wrong (crank shell size, threads etc) than a front or rear wheel motor.
Recently I converted my carbon road bike to electric with a ~350W front wheel motor. One of the biggest challenges and risks was to strengthen the forks, achieved using a torque arm either side with 3D printed sleeves to protect the carbon forks. So far this has worked very well. Another concern was fixing the heavy battery case, which is a front tube bullet, quite similar to the one you used. However the tubes are a much larger diameter carbon. So again, 3D printed clamps provided a solution. Controls are really simple. Just a couple of on / off switches in the right places and a 4 position power switch. This required developing a little pulse width modulation control board using a microcontroller, also to provide a kind of cruise control. Otherwise no sensors apart from the motor itself. Really enjoy riding the machine, including up steep hills that would otherwise be impossible at my current level of fitness. Cheers Ron.

tu2thepoo 4 years ago

That's super cool! I don't have access to a 3D printer so that ends up with me doing a lot more gluing and zip-tying than would be optimal for a clean design. Do you get any torque steering effects with a front wheel drive?

kiwironnie 4 years ago

Undoubtedly there are lots of ways to effectively add material to carbon (or aluminium) forks to spread the load. If you don't want to bond stuff on there, maybe make a mold to cast a plastic shell. However the 3D printer was also used to make other parts, including thrust washers shaped to fit the flats of the motor axle. Also, switch and control housings that clamp to the handlebars, incorporating the motor control display. Frankly there was a lot more to do to complete the job than anticipated. For example the dropouts had to be carefully filed to accommodate a significantly thicker axle than is standard on a road bike.
With regards steering, there have been no ill effects. It all works well. The motor torque is applied quite smoothly on switch-on, i.e. a soft start. However 350W at 36 volts is probably about the largest motor that I would consider fitting to a front wheel (a Cute Q100C was used). For more power possibly another motor fitted to the back wheel, or better still a crank drive as in this Instructable!

gadgeteer123 4 years ago

Thanks for the information. Just a word of caution. There are two types of forks that are not suggested to be used for a front hub motor. One is a suspension fork and the other is carbon fiber. Carbon fiber is not strong enough to sustain the rotational torque of a geared hub motor. I'm sure that it is functional, but just a word of caution to those who are wanting a larger hub style motor. Steel frames are the best since they have some flexibility unlike aluminum. Road bikes are designed to be light and strong but not strong enough for the rigors of additional stress on the frame. Enjoy.

kiwironnie 4 years ago

Yes, you are right of course about 'suggestions' of materials that could be a problem. However much of the information around on this topic is untested. There is a great deal of force on forks when a heavy rider is braking down hill, yet aluminium and carbon fibre road forks remain in tact. Clearly though the force from a powered hub is applied differently, so a specific design solution is needed to account for the weaker, stiffer materials. My approach has been to use 3D printed sleeves to spread the load of torque arms fitted to both forks. The sleeves were designed to fit the profile of the forks, effectively increasing their thickness, with the twin torque arms halving twisting force on the dropouts. Certainly if I was starting from scratch then a steel frame would have been the choice. However I've proven, to myself at least, that suitably augmented carbon forks can be made to work.

Gusgonnet 4 years ago

admirable work, congratulations!!!

tu2thepoo 4 years ago

Thanks! It was a lot of fun overall, definitely some times when I tore my hair out :-)

samham001 4 years ago

I bet I could do this on my unicycle. Can't be that hard on one wheel, right?

Kardolf 4 years ago

Why use a mid mount drive system instead of a wheel motor? Or did I just miss that in the article?

gadgeteer123 4 years ago

A mid-drive motor allows one to have various speeds on the rear cassette hub. So besides the extra energy that it supplements to the pedal crank, one still gets to select lower gears for hills and taller gears for flat land with more speed.

tu2thepoo 4 years ago

Good question! Generally speaking, mid-mount motors are a bit more efficient climbing up hills, so you'll have less heat and power draw. That helps increase battery and motor life.

The more frou-frou explanation is that the mid-mount motor helps preserve the weight distribution of the original bike, and a lot of people riding road bikes are very aware/sensitive to changes in handling/weight distribution.

So in short, rear wheel hub motors draw more power going up hills and can make the bike handle (more) differently than before.

johnip4 4 years ago

I’ve converted 2 cross country bikes. The first one I used a front wheel motor. It’s ok but the peddle assist sensor doesn’t fit with an ISIS crank set. It’s my wife’s bike so I the triangle was too small for a battery so I used a seat post mount. The bike is a bit top heavy. Due to the lack of the PAS, she has to use the throttle to get assist.

On my bike I used a mid mount Tongsheng TSDZ2 motor. The main difference between it and the Bafang motor is that it uses a crank torque sensor, the harder you peddle the more assist you get. Both of these motors give you a lower center of gravity than a wheel motor.

We’re both in our 60s and the ebikes allow for longer rides and we can take on hill climbs that we avoided before.
We love them!

tu2thepoo 4 years ago

That's cool! I had considered a hub motor setup, but I'd already blown too much money on upgrading the wheels to just get rid of them :-D

billbillt 4 years ago

Great Job!..............

Schermpje 4 years ago

Great intructable!
Very... instructive.

Been looking for a similar solution for my (very much loved) mountain bike, to get a little more use from the poor thing. This helps a lot :)

tu2thepoo 4 years ago

Thanks! There are a ton more guides for mountain bikes, so consider mine a stepping-off point!
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