Converting a road bike into an electric bicycle
This is the guide I wish I had when I was researching how to convert a 2013 Giant Defy road bike in to an electric bicycle using a Bafang centre drive kit.
When I started I knew converting a road bike to electric wasn't too common and that there would be difficulties. I had to read heaps of different blogs and watch lots of videos to figure out how to convert the bicycle. I managed to get it all working in the end and thought this retrospective might help others out!
Everything I needed for the project
Components
- 1 Giant Defy 2013 road bike - bottom bracket removed by bike shop
- 1 BBSHD Bafang motor
- 1 52v Panasonic 13.5ah GA Shark Pack
- 1 Lekkie BBSHD Bling Ring 42T Red
- 1 set of Bafang disc brake sensors
- 1 custom bottom bracket adapter
- 1 pack of bottom bracket spacers (variable widths combined to 10mm)
- 1 Bafang gear change sensor
- 1 DPC-18 colour display
Tools
- Pedal wrench
- Bike tool (Allen keys)
- Chain breaker
- Power drill (or Dremel if you have one)
- Pliers
- Snips
- Metal file
- Hacksaw
- Bafang installation tool
Consumables
- 80 grit silicon sandpaper
- Cable ties
- Epoxy for connecting the brake
- Black electrical tape
- Cable tidy
- Blue Loctite
- Plastic bumpers
The Bike
I've recently upgraded my 5 year old Giant Defy bicycle to a beautiful Cannondale Synapse. I have some great memories on the Defy cycling around New Zealand and Europe fully loaded as a tourer and I've gotten some serious use out of it but it is quite beat up at this stage.
I have 15 km bike commute here in Auckland. Lately I see more and more folks on electric bikes whizzing past me on the way to work not even breaking a sweat so I built an electric bicycle to replace my motorcycle for commuting on the days I don't feel like riding a standard push bike.
Instead of just selling it on TradeMe for $100, I thought I could get a few more years out of it with an upgrade to an electric bike and save some petrol money this year too.
If I was building an electric conversion again I would buy a bike specifically to upgrade instead of doing it this way on the Giant Defy. The bottom bracket's size and drop bar brakes are hard to work with on a modern road bike.
Choosing a motor
There are two common types of motors you can buy to convert your bike in to an e-bike. Mid drives and Hub drives and they all have different power options. I went with a Bafang BBSHD 1000W mid-drive unit. There are better options than this one with less power and cost but they wouldn't fit on my bike. Getting a smaller motor means it's cheaper, lighter and uses less battery power. So get the smallest you can in my opinion.
Quick note on hub drive motors
A type of motor you could choose is a hub-drive system. Hub drives are essentially a wheel you buy that has a built in motor. You pop the wheel in your bike and plug in a battery. It's really convenient to install this type of bicycle conversion kit if it works for your bike.
I've read that there are some disadvantages with this type of motor around the way they feel to ride along with. They don't work well with gears and don't feel natural. Hub drives can understandably make changing the rear tyre a pain with the weight of the motor too. If you use Schwalbe Marathon Plus tyres you won't be fixing punctures very often but I can still understand the weight issue, motors are heavy. I've never ridden a hub drive myself though so this info is all from articles I've read online.
I had some really nice Mavic wheels on my bike and I wanted to keep using those so changing one out for a hub drive was out of the question.
The second common type of motor you can buy is the mid-drive motor pictured in the previous section. These types of motors replace the drive system on your bike. You'll get a motor that replaces everything that's in your bottom bracket including a new chainring and cranks.
Choosing a brand
I did a couple of nights of research on brands and Bafang or "8fun" kept coming up. I looked in to other brands a little bit but there were always negatives compared to Bafang. Availability in New Zealand included. One of the more promising ones that can retrofit an existing bike is the Tongsheng tsdz2 500W but it wouldn't fit my weird bottom bracket and didn't seem as reliable as the Bafang. It was cheaper though.
There are some really well known names like Yamaha and Bosch making great e-bike drives but they are for frame manufacturers. You can't retrofit them on to existing bikes. The frames are designed and built around those motors rather than the other way around.
Some good forums to do your own research are
https://www.reddit.com/r/ebikes/
The Bafang drives are available from reputable resellers here in Australasia and are widely available on Ali Express too. The Bafang company itself is notorious for not responding to direct contact on their website though so you are better off going through a reseller imho.
These resellers also sell all the spares and accessories you will need, usually as a package. There's also heaps of videos and blog posts like this one describing bafang installations for various types of bikes to show you how to install the drive so it kind of makes sense to just get the most popular drive and save yourself some hassle.
Choosing a motor model
So once I decided on the brand the next step was figuring out a model. Bafang have three main models. The BBS01 is a 250W motor (some vendors tune it up to 350W), the BBS02 is a 500W or 750W motor and the BBSHD is a 1000W motor.
Bafang accessories work across all the motors so your decision should be based on what power you need, legality of the motor in your area and if the motor will fit on your bike.
Legal limit for motor power
Many countries have a legal limit for e-bike motor power on public roads and some have a speed limit also. Across Europe the limit is often 300W or so. Most bikes from the big manufacturers like Bosche, Trek or Specialized are 250-300W. That's because this size motor works great!
These 300W bikes still get people around quickly and efficiently, the motors and batteries are light and the batteries last a long time. You might not need the biggest and baddest motor on the market unless you are riding in a very hilly area. The higher the output of your motor, the faster you will use your battery power. I would have gone for 500W if it would fit on my bike.
Bottom bracket diameter
The second really important consideration for buying a motor is will it fit in your bike? To check this you have to measure the bottom bracket on your bike with a ruler or callipers. You can get a rough measurement without taking anything off the bike but it's even better if you can get the bottom bracket completely out to measure.
The Bafang motors are designed to fit in a BSA threaded bottom bracket that is 68mm or 73mm wide (that's the distance between where the two cranks connect to the frame) with a 33.9mm diameter (the diameter of the hole in your frame). If your bottom bracket is skinnier than 33.9mm you will never be able to get the motor on to your bike. If your bottom bracket space is larger than 33.9mm diameter you will need an adapter to fill in the space.
You want to turn your bottom bracket diameter into BSA diameter to fit the motor. You can see some common bottom bracket descriptions and dimensions here: https://wheelsmfg.com/bb-standards. Some of those ones, especially the asymmetric bottom brackets are going to be REALLY difficult to work with. Maybe reconsider the bike you have chosen unless you have direct access to a lathe to make an adapter.
My Giant Defy has bottom bracket that is roughly 41mm in diameter. I had to buy a custom aluminium adapter from Luna Cycles that I put in the bottom bracket space to turn it in to BSA diameter.
You can also buy off the shelf adapters for some bottom bracket types to turn them into BSA. They typically only work bottom brackets that are the exact width of BSA and you are only changing the diameter. So this leads us to the second problem...
Bottom bracket width
BSA bottom brackets are usually 73mm wide and the Bafang motors are designed to support this width. My Giant Defy has a ~90mm wide bottom bracket. The BBS01 and BBS02 will only work in 68mm or 73mm bottom brackets.
The BBSHD is the only motor you can get that fits wider bottom brackets such as 100mm and 120mm. It comes in multiple sizes to accommodate more bikes. Most vendors of Bafang products only sell the standard 68mm and a larger 100mm. Bafang sell some other sizes like 90mm and 120mm but not all vendors sell these to keep stock under control I guess. You can get a motor that has a fitting that's slightly longer than your bottom bracket width and use aluminium spaces to make it fit correctly.
This is what I did for the Giant. I bought a 100mm motor and used an adapter to make it 41mm diameter and used roughly 7mm of spacers to make it fit snuggly with its bracket. Please note that you don't want to get a motor that requires too many spacers because it ruins your chain alignment by pushing out the chainring. Mine is borderline OK and I can't use low gears. I probably should have gone for the 90mm direct from China but my electric bike does work OK, it's just not optimal with the chainring alignment.
So if you have a road bike. And it has a weird, wide bottom bracket (wider than 73mm) then you have to get the BBSHD. And you have to make sure you get the correct width. You have to have enough threads on the motor coming out the side of your bottom bracket so you can secure it to the bike frame. But you can't have too much extra width requiring spacers (more than 10mm imho) or you will ruin the chain alignment.
If you have a fat bike or some mountain bikes with a wide chain stay, you also have to make sure the cranks and chainring will fit and turn without hitting your chain stays.
I almost purchased my motor from Ali express but I noticed that the seller actually sold the 120mm Bafang model with spacers to get it to the length you ordered. This is a terrible solution because the spacers ruin your chain alignment.
When you're purchasing the motor make sure that you are actually getting the specific length motor and not a 120mm one with spacers.
Choosing a vendor
There are lots of resellers of Bafang motors. In my research I found one company getting recommended all the time - Luna Cycles. This is a US company that resells bafang motors and all the accessories you might need. They have some kind of partner company in Australia called Luna Mate that sells similar kit to us down here in Australia and New Zealand.
I had already ordered some tools and parts from Ali Express before I found this company, if I was doing it all over again I would just order everything I could from Luna because they deliver really quickly and you have everything in one package so you can build your bike right away.
I paid NZD $1,850 for the BBHD, a huge 52V 13.5Ah battery and a great colour screen. I also got a brake sensor kit, a programming cable, a spacer kit, a throttle and a fancy Lekkie Bling Ring 42 tooth chain ring. Everything went super smooth and delivery was a week or so. I could have saved roughly $400 by purchasing from Ali Express but I was afraid I would have to deal with customs and sending back a defective unit would have been a pain in the ass! Luna Mate also stock batteries in Te Anau so you don't have to deal with customs and mine was delivered in like 2 days.
I highly recommend Luna Mate!
Choosing a battery
For the BBSHD you need at least a 48V battery. I went with a 52V because that's what Luna Mate had available. Other than that get as much battery (Ah) as you can afford I guess. Battery lifetime is in charging cycles so if you have to charge less often you should get more life out of the battery. I think you get something like 1000 cycles out of a battery so judge lifetime by your commute.
I don't know much about batteries but there are some interesting YouTube videos comparing different voltages and such. I was happy to go with the choices on Luna Mate.
The "Bling Ring"
You can buy a special chain ring called a Bling Ring for the Bafang electric motors. I recommend getting one. It's much lighter than the chain ring provided by Bafang and the chain fits the teeth FAR better. This means there's much less chance of an unexpected chain derailment. They also have less teeth than the default chain ring which puts less strain on the motor and makes for a smoother take off. On top of all that they look a lot better too :)
Sizing the battery for your bike frame
You can get batteries in different packages. They can be mounted to your pannier rack, on the down tube or in a frame bag. This kind of depends on your bike. I went with a downtube battery. The bracket screws in to a bottle cage mount. It's all pretty neat and easy really.
I added some rubber bumpers to the bike frame where the batter bracket could flex to help give it more stability. The bumpers are usually used to stop press doors from banging shut. 3M make them and you can get them in any hardware shop.
If you have a mountain bike the downtube battery may not fit inside the frame triangle so you need to get a triangle battery and a frame bag. Some people mount the batteries underneath the downtube. If you have a compact road bike frame, make sure the pack and bracket can fit on a bottle cage bracket without hitting the seat tube. I didn't measure this and there is only like 5mm of clearance. I was just lucky!
Installation
Bike setup
You need make space for your new motor by removing the bottom bracket. Mine requires a special tool so I just asked my local bike shop to help. They did a fantastic job and even cleaned out the bottom bracket for me. If you have a press fit bottom bracket and don't know what you're doing you can damage the frame so be careful or get help!
If you look into the bottom bracket space there might be some spot welds or screws protruding into the space. This will prevent the motor and adapter to fit through easily so you need to sand them down until the motor and adapter fits through.
My bottom bracket tapered a bit towards the middle so I also had to sand a little bit off the diameter of the adapter I received from Luna Cycles to make it fit. I used a drill with sandpaper wrapped around a drill bit to do the inside of the adapter and the inside of the bottom bracket. This is stupid and dangerous though, use a Dremel tool if you can.
The bottom bracket adapter I ordered was also too long (my fault) so I had to hacksaw off 5mm from the end and file it down to be smooth. You need to have the adapter fit just inside the bottom bracket. It shouldn't protrude out the side where the teeth of the motor bracket need to bite into the bike frame. Better to order too long from Luna Cycles though imho.
You need to completely remove the front derailleur. Just unscrew the bolts holding it on and break the chain to remove the derailleur from the chain. I just snipped the gear cable. You wont need it again.
On my Giant there was a plastic cable guide on the underside of the bottom bracket for the derailleur cables. This was too big for the motor to fit so I removed it, cut off the larger side and put it back on in reverse. Be careful here as this screw fitting is very fragile. It's a steel bolt (strong) directly into the aluminium bike frame (very soft) so if you tighten it too much it will tear the threads.