Weekend project: How to build your own DIY 40 mph fast electric bicycle
Electric bicycles is a booming industry. It seems like every week we hear about another new model entering the market. Outside of a few exceptions, most electric bicycles fall in the 15-28 mph (25-45 km/h) range. That’s fine for pleasure riding, but it leaves many enthusiasts looking for more speed.
With so many people commuting on electric bicycles, the extra speed of a fast electric bicycle is a nice addition for many, allowing them keep up with traffic. However, there aren’t many commercially available options for fast electric bicycles. That’s why I decided to build my own, with the goal of reaching 40 mph (64 km/h). Read on to see how to build your own DIY fast electric bicycle.
[Disclaimer: Fast electric bicycles can be dangerous. Please do not attempt to build your own high speed e-bike if you do not already have experience building custom electric bicycles. Please start with a tamer, more reasonably-powered electric bicycle first.
Additionally, please check your local laws to determine if a fast electric bicycle is legal in your area. Depending on local laws, this could be an “on private property only” project, or may require adding mirrors and lights before registering as a moped or light motorcycle.
Lastly, there are multiple safety advisories peppered throughout this article. If you plan to build a fast electric bicycle, please pay attention to every safety advisory.]
Choosing a donor bike for a fast electric bicycle
Component choice is critical, as this is what will make your e-bike safe and effective.
We’ll start with the donor bike, which we’ll convert to an electric bike. I recommend using a full suspension bicycle when building a high speed electric bike. Full suspension smooths out the ride and can keep you from getting jarred when hitting a pothole at 40 mph (64 km/h). However, please do not use a cheap department store full suspension bike.
I’m using a Motobecane Jubilee FS bike, which costs around $600. This is a nice balance between a full suspension bicycle that has high enough quality to be safe, while not breaking the bank with a $2,000 bike. One component I would have liked to have on this donor bike is hydraulic brakes, which would be nice for stopping at these speeds. But decent Shimano hydraulic brakes can be found for around $70 to add to any bike.
Another good option would be to start with a used downhill bike. Downhill bikes are built to handle extreme terrain and thus make great high speed electric bicycles. A used downhill bike will still be high quality, but won’t have the same high price tag.
A quick note about donor bikes: no bicycle brand will condone you turning their bike into an electric bicycle. Each will have some generic statement about how this voids their warranty and the bikes weren’t designed for such applications. This is definitely true, any sort of tinkering will void your warranty. However, if you start with a high quality bicycle, you can still build a safe machine. High quality mountain bikes were built to handle speeds over 40 mph because you can easily hit those speeds on hills, though you may want to upgrade your brakes if you’ll be sustaining such speeds. The frames are rugged because they are meant to bounce off boulders and tree roots while racing down mountain trails. Thus, 40 mph on a smooth street is definitely within the design tolerances of a good quality mountain bike. Yet another reason not to use a cheap department store bike.
In the video below I show the bike I chose, then I demonstrate the building process and test out the final e-bike.
Choosing an electric bicycle conversion kit
Electric bicycle conversion kits contain all the bolt-on parts you’ll need to convert a standard bicycle into an e-bike.
If you want to go up to 30 mph (48 km/h), you can find many kits as well as batteries to handle that job. Generally speaking, you’ll be looking at a 1,000 W direct drive kit and a 48V Li-ion battery.
For my fast electric bicycle though, I am going to choose a 1,500 W kit from West Coast Electric Cycles, based in Washington. For a kit that requires such speeds, I feel more confident buying from a local company with a good reputation. I spoke with WCEC’s owner Barent Hoffman about my project goals, and he helped me find the right kit as well as the Motobecane donor bike. Barent has been building fast electric bicycles for years, and stocks crazy high power kits at WCEC. The 1,500 W kit I’m using is actually the tamest of his options. Many of his customers are electric bicycle racers.
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