Originally Posted by 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.
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.