Fishstalker

Hey all, not sure if this questions been asked before, or if its even a smart question at all but. Is it possible to turn a BMX bike into an electric bike? Im thinking about it because BMX bikes are robust, small and you can carry 1 more person on it with those foot pegs hehe.
But back to the main point, im just wondering if its possible as im not really sure about axle sizes and hub widths and any other differences between a BMX and say a MTB or something that may affect a conversion. So if anyones done it before or knows anything about it, your feedback would be greatly appreciated.

Thanks a bunch guys.

paul-yokaholnes

I would love this.. seen a few add ons on ebay which might work.

nwmtnbkr

You can add an electric motor to any bike. That said, there are issues you need to consider, especially if you go with a larger motor with lots of torque. Safety issues need to be factors in your decision, not just speed and power. Some people consider all hub motors unsafe because of the affects of the torque they generate. You can read long discussions about this at the Endless Sphere e-bike forums. The one thing that everyone will agree upon is that you absolutely cannot use a hub motor on an aluminum fork or a suspension fork. They have cast drop outs that can and will fail without warning, even with torque arms, causing you to loose control of the bike as well as serious injury.



Steel drop outs can fail too, so you'd need to keep inspecting a front fork frequently. You need to use torque arms for any hub motor. It's a necessary and worthwhile investment.

There are non-hub motor kits. If you live in a hilly area, they have a big advantage in that they produce much more torque. I installed a Currie conversion kit on my mountain bike this summer to help me on the hills. (I retired to the far norther US Rockies--I'm west of Glacier Natonal Park.) I love this kit--it's enabled me to ride my bike without knee pain and I'm riding my bike daily (except in extremely severe winter weather). There are several non-hub motor conversion kits available. Many people like to build their own, ordering inexpensive electric motors and parts from various sources (especially those that stock parts for electric scooters). If you're so inclined, I'd suggest you go to the Endless Sphere forums--they've got several on e-bikes, including one that specifically focuses on non-hub motors. (You can gets lots of help if you decide you want to build your own system.)

If you're looking for speed and no pedaling, I'm afraid you're going to be disappointed. Battery technology improvements have been slow and the batteries present the biggest issue in any e-bike build if you're wanting maximum speed. Many have embraced LIFEPO4, which uses iron phosphate, which is a safer cathode than Li-POLY or even LiION with either cobalt or magnesium oxide. It is lighter than traditional SLAs and can be recharged much more often before it will loose it's capacity. However, it is still a very expensive. If you want to go extremely fast, you'll probably be needing a 48V 20AH battery at a minimum. With shipping from China, that's probably $700-$900. Even with that power, you'll probably only get about 2 hours runtime, depending on how hard you hit the throttle. (A rule of thumb is that you get 1 hour run time for each AH the battery is rated.)

Now, whether your existing bike frame and components are adequate to make it a candidate for a safe e-bike build is often an issue people don't discuss. However, it's as important a factor to consider as specs for the components of an e-bike conversion kit. There's a reason that Congress mandated that ready-made e-bikes that can travel over 20 MPH and/or have motors with more than 750W must meed safety standards for mopeds and motorcycles set by the National Highway Transportation Safety Administration. Those safety standards are drafted to minimize frame failure due to torque and improve handling as well as mandate safety features, such as good brakes, turn signals, lights, horn, etc. At present, kits are caught up in the safety standards issues, but I think it's only a matter of time before the sales of kits get regulated since some powerful motors are being imported and sold. If you want to install a motor that will allow you to travel more than 20 MPH, your bike really needs disc brakes. If you don't have them and cannot add them as an after-market add on, then maybe you need to buy another bike to build your e-bike. If your existing bike is very light weight aluminum or carbon, you might really want to get another bike for the e-bike build.

Good luck. Read, read, read and take your time shopping. If you are thorough in your research, you should be able to build a safe e-bike that you're happy with.

Fishstalker

Wow theres so much i need to consider. Luckily i havent bought anything yet as im still taking my time to research all possibilities so i can get the best value for money and so i dont die the moment i turn the motor on hehe. But as far as i can tell here in australia the legal limit for a electric bike motor is 200w so i dont think itll cause too much trouble. I was thinking of getting a 24v 200w motor and a 24v10ah battery (not sure if itll get me the distance i need, im planning on riding about 16 miles round trip), just the most basic level as i was planning on doing most of the pedaling. The BMX in consideration will most likely either have a chromoly or Full Hi-Ten (not sure what that means but im assuming high tensile steel) fork, no aluminium there.

With that information in mind im guessing that it should be fairly safe though i cant be too certain which is why ive come here to ask for advice =D.

nwmtnbkr

You should do fine, especially since you want to pedal. I plan on building a LIFEPO4 battery over the winter, but I've not had issues with the SLA pack that came with my kit not getting me far enough. However, I pedal and use power assist on the hills here. I've gone over 25 miles and still had power available in my SLA pack.

There are so many 1000W motors (and even higher powered) showing up on e-bay, many people are ordering (from posts in various forums it would appear that even those living in your country or the EU have been able to order these powerful motors from China and they aren't being seized by customs officials--perhaps because they don't realize that the motors will be used for an e-bike). I would suggest that you check out the Endless Sphere forums. You'll learn a lot and the members are very knowledgeable and willing to help with technical problems. One of the senior members, who is a fellow countryman of yours, has a very interesting build going on. His e-bike/motorcycle build is awesome. I'm amazed at the level of skill of many of the members at Endless Sphere. Here's a link to the thread on that particular build. https://endless-sphere.com/forums/vie...p?f=28&t=12810

ekline309

There are actually quite a few issues that make building an electric BMX more difficult than a traditional electric mountain or road bike.

1. Rear frame width
BMX frames are traditionally 110 mm vs 135mm or so for mounting and road (and most hub-motors). You will probably need to modify the frame to accept this sized hub and use corresponding crank spacers to move out your sprocket.

2. Rear gear size
If you do get a rear-hub motor to fit you will probably be stuck with a traditional freewheel which (I believe) only goes down to 12T. To get 25-9 gearing you'll need to run a 33T in the front (not so bad but a little big).

3. Space for batteries
BMX frame triangles have gotten smaller and this won't leave much room for a battery and a controller. Not a deal breaker but also not ideal.

4 Mid-drive Q-factor
If you opt for a mid-drive like all the quality eMTB bikes are doing you might have a Q-factor issue (which is the distance from crank-arm to crank-arm) since the rear hub is narrower than mountain and road bikes. I'm not 100% certain about this but something to think about.

There are actually quite a few fat-tire bikes you can get today that I would call BMX "inspired". I would recommend taking a look at them here.

Hope it helps,
Eric

Doc_Wui

The original question was asked about 10 years ago. Battery technology has changed. The electric vehicle world is using the more volatile lithium chemistry, with layers of electronic safe guards
However, the axle widths still restrict what can be done with hub motors unless one is willing to bend a steel frame. And while batteries are less expensive, they are still harder to fit on a small frame afterwards. STill, it's easier t oday t o motorize a BMX than it was 10 years ago.

ietours

Me and my friends have lots of electric bicycles in Vietnam. We often bike together on weekends

linberl

With a 16 mile range, and intention to pedal and not throttle, you could just put a friction drive on your bmx. Easy to add, you might wear tires a bit more often depending on the drive. If you plan to ride in heavy rain or snow, probably not gonna work for you. Endless Sphere can help you make your own (Kepler might still be selling his kit) very inexpensively. There are some commercial ones available as well (OneMotor, Alizeti, Add-e, Go-e, Rubbee). Folks have been using them on folding bikes (small like bmx) for a long time, Brompton/Hidden Power for example.