Extensive Hands-Off Experience: Installing the BionX Electric Assist

I consider myself The World’s Leading Expert on BionX Retrofits… who has never actually done a retrofit himself.

In a previous post, I talked about the natural ride of BionX — and I referred to bikes that come from the manufacturer with the BionX system already installed.

But what about someone who wants to put the BionX system on their existing bike. That’s the retrofit scenario.

If you are considering a BionX retrofit for your bike — maybe doing it yourself — this will let you know what you are getting yourself into.

At Campfire Cycling, we sell these kits on our Bike Tech Shop. Our practice is to know what we are talking about, and to write authoritative product descriptions.

BionX Axle Collar Puller Tool
What is this? Who needs it? I’ve never touched one, but I know.

After a whole bunch of research on every single part, accessory, and option for the  BionX Kits that we sell, I wrote the product descriptions. I did so knowing that bona-fide wrench-turners would be reading these descriptions.

You can either trust that I know my stuff when I talk about the retrofitting, or you can patiently humor me as you would a priest who is giving you marriage advice. For some people, that’s plenty authoritative.

So how difficult is it?

Have you ever put together furniture from Ikea — with just a screwdriver, a hammer, and the hex wrench that came in the box? Did you get it right on the first try?

It’ll be harder than that.

Have you ever installed a pacemaker into a patient with an underlying myocardial infarction?

Installing a BionX system won’t be that hard.

I’m certain that, with my skills, I could do a BionX install.

If I were to try it, I’d set aside a long afternoon. I’d make sure I had a fresh box of bandages and some antiseptic nearby. And I’d bring my laptop computer into the garage where I could watch this instructional video again and again.

Flagstaff Bike Revolution
Link Love for Flagstaff Bike Revolution

For perspective, I spoke with a professional mechanic, Adam Cornette at Flagstaff Bicycle Revolution, where they’ve done many BionX installations on bikes for their customers. Adam told me they can do a BionX install in about an hour.

One hour.

It takes me half that long to patch a tire — under ideal conditions, in my garage, with my work stand and all my tools handy. If I’m in a good mood.

So you might think about your skills and the value of your time, and weigh it against the DIY self-satisfaction that you anticipate having. (Focus on self-satisfaction — because when you boast about having done the retrofit yourself, nobody else will care.)

Are you still up for this?

Do you still want to do this yourself? Or maybe you want to walk into your local bike shop carrying the kit all the right parts they will need.

Here are some things you’ll need to figure out:

Battery on the Downtube or on a Rear Rack

Do you want a battery that mounts to your downtube or one that mounts to a rear rack? Personally, I prefer the look of the downtube mount, and I like that the weight of the battery is down in the middle of the bike, which improves handling.

Technically, the mounting bracket for your downtube requires two bottle cage bosses to mount. If you don’t have these bosses in your downtube, you don’t necessarily have to add them. Adapters are available — but I hear tell that hose clamps work just fine.

BionX PL 350HT Electric Bike Conversion Kit
Downtube Mounted Battery

Surprisingly to me, rack-mounted kits are more popular, according to Ryan Cate at Quality Bicycle Products — and he would know. If you buy a BionX kit in the USA, it probably got to your local bike shop or to your favorite online retailer via QBP.

I find the popularity surprising because the rack-mounted kits almost always mean you forfeit your favorite rear bike rack, and instead use the BionX Rear Rack with Docking Station. Additionally, you end up always having eight-ish pounds on your rear rack before you ever mount panniers or a rack-top bag.

BionX PL 350HT Electric Bike Conversion Kit
Rack Mounted Battery

Of course the frame design may be the constraint that makes a rack-mounted kit the only option. Me? I just don’t like the looks of it.

Hey! You with the weird bike…

Recumbent Tandem with Bionx Rear-Rack Mounted Battery
It had to be blue: A BionX-Powered Recumbent Tandem Folding Bike | Photo: Swann Electric Bicycles
Bionx Wire Harness Sizing Guide
Bionx Wire Harness Sizing Guide (PDF)

I’ve seen photos of BionX kits installed on just about everything from folding bikes to recumbents to tandems to long-tail cargo bikes.

Bikes with weird geometry or long cable runs may need either a Motor Cable Extension or a Communication Cable Extension.

This Bionx Wire Harness Sizing Guide will help you determine what length extensions you will need, if any.

And if you do have a weird bike, all bets are off with regard to the time you’ll need to do the install.

For Bikes with Non-Vertical Dropouts

Normally a bike’s rear axle is pretty passive. It just has to hold your wheel in place, and maybe keep your chain properly tensioned. There are no forces making that axle want to turn.

BionX Torque Blocker
Non-Vertical Dropout Diagram

But when the power to your bike is coming partially from inside your hub, that can cause your axle to want to turn in an opposite direction to the rotation of the wheel.

So the BionX kit is designed with a tab-like thing that juts into the dropout slot to block any torque on the axle from the motor. If you have vertical dropouts on your bike, the kit is ready out of the box.

For some reason, however, it’s critically important that this little notch in the hollow BionX axle be pointed straight down.

So if you have non-vertical dropouts on your bike, you will need either a BionX Axle Collar Puller Tool (a $24 tool you will never use again — only for the PL 250 or PL 350 kits), or you will need to select an angle-specific torque blocker (for the SL 350 HT kits). These will allow you to adjust the BionX axle, and properly orient that ever-important notch.

If that didn’t scare you, maybe you are up for this retrofit project.

Your Freewheel Might Not Work

SunRace Threaded Multi-Speed Freewheel
A SunRace Freewheel compatible with a BionX Hub

BionX kits come with a pre-laced rear wheel to replace your existing rear wheel, and the motor is built into the threaded hub.

If you’re lucky, your existing bike already has an ISO thread-on freewheel, and you can use it on the BionX hub. Otherwise, you’ll have to acquire a compatible threaded multi-speed freewheel, such as this one by SunRace.

And, of course, you will need to readjust your derailleur after you get it all put back together.

You do know how to adjust your derailleur, don’t you? Or is that pro bike shop starting to look good?

For Most Handlebars

Tektro Linear Pull Brake Lever Set for eBikes
Look Ma. No zip ties!

There are sensors and a magnet that need to be installed on your rear brake levers, which is accomplished with (I kid you not) zip ties, mounting tape, and superglue. Weird, huh? But that apparently means that the sensor can install on a wide variety of brake levers.

But if it were me — the guy who would rather throw money at professional bike mechanics — I would just buy a Tektro Linear Pull Brake Lever Set for eBikes and replace my old brake levers. The Tektro levers have all of the electronics built in. If these levers will work for your handlebars, I’d consider it $46.99 well spent.

For Bikes with Drop Bars

If you have a bike with drop bars, there are all kinds of reasons why the sensor mentioned above might not install well on your fancy brake levers. And, sorry, those Tektro levers aren’t made for drop bars.

The alternative is the BionX Inverse Magnetic Brake Switch, which installs on your top tube and brake cables, instead of on the brake lever.

BionX Inverse Magnetic Brake Switch
Inverse Magnetic Brake Switch

If you install the standard magnet and sensor (the one that comes with the kit) at this location, the BionX system will want to do the opposite (inverse) what it should do when you are braking: The motor will only want to assist when the brakes are engaged. Which is kind of the opposite of why most people would want an e-bike. And that’s why you would need an inverse brake switch.


Hey. I’m not trying to intimidate you. I’m not saying I’m intimidated by this; I’m saying I’m lazy. I’m exhausted from just writing all this. The fact is, I’d love for you to buy a BionX kit and all the related accessories from Bike Tech Shop. I just want you to know what you will be getting into.

If your skills are as good or better than mine — and your ambition is definitely greater than mine — you can do it.


Find a good bike shop — preferably one with a mechanic who has done a BionX retrofit before. Remember what I said above about QBP? If a bike shop has a QBP account, that’s a good sign. Don’t be afraid to ask.

Have you done a BionX retrofit? Did I get anything wrong? Let me have it in the comments.

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