What motor would you install in bmx bike?

Hi, im brand new to the forum. If this post violates any guidelines please remove it. Ive chosen the donor bike for my ebike, a 20 inch bmx bike. Im wanting to put suspension forks for 20 inch tires on the front.
Because its a 20 inch it seems pretty complicated to have disc brakes installed. I was wondering if v brakes can work apropriately for an ebike. I was originally wanting to install a rear hub motor but i am confused about installing it on a single speed bike and also dont want to stretch the rear dropouts as ive seen on other bmx ebike builds. I want to install a bafang bbs02 on this bike because it seems like a good product, but ive seen in the forums that people say its pointless to put a mid drive on a single speed. What would you do to my bike?(hub motor reccomendations, opinions on the mid drive)

Welcome to the forum.

Your brakes are fine. Any brake that can skid a tire is capable of maximum braking force. And Vbrakes are better for super fine, low speed control like you need on a BMX trick bike. Best motor depends on how you want to ride the bike. If it's going to be a park cruiser, then you'll need something wildly different from something you plan to take to the Bonneville Salt Flats and try to set the worlds record for the fastest BMX Bunnyhop.

A BBS0x without rear gears is like a girlfriend without boobs. Sure, you can ride it, but a good part of the fun and utility will be missing. Same is true of the bike.

You said you don't want to spread you frame, and that tells me that you care about this frame. If you like this bike, don't convert this one. Adding the motor, battery, and all the paraphernalia that goes with it will easily double to triple the weight of the bike, ruining it as you remember it. Instead, buy a cheap garage sale or thrift store $25 bike. Once you have a motor on the bike, you won't notice that it wasn't as good of a bike as yours.
.... And then spread the rear of the frame. Either you're going to want to stick a set of gears back there for a BBS0x, or you'll want a hub motor. The thing you don't want is a front motor. I have one of those in a 20" bike. It's useful, but it's easily the least favorite Ebike out of the dozen or so I've built.

Yep, get a frame you don't mind stretching to 135mm, or at least wide enough with a single speed gear on a rear hub motor. Steel bike. Add brake mounts to it with a welder, disc or rim, for a rear brake.
My first bit of advice is very very often this, don't convert your favorite bike.


I find it kinda odd, that all these years later, they still don't have cheap hub kits for bmx bikes all over ebay.

I would suggest taking a serious look at the 20-inch Golden motor "Magic Pie". The controller is integrated inside the hubmotor, so only the throttle and battery are separate.

It has limited hot rodding potential, but there is nothing wrong with it in the stock form.

The magic pie was my first choice, specifically the non vector one(sold out currently), but it said something about using a 7 speed cassette. Can a single speed cog be used on it and will i still need to stretch the dropouts?

And for the record i have no qualms about motorizing this bike, i just didnt want to have to spread the dropout out of laziness and fear of not having the right tools or doing it wrong(not because im sentimental about the bike) and one of the reasons im considering a bbso2 is that if i choose to jump i wont be landing on the motor itself(keep stress off the hub)

Maybe you might like it a bit longer, with a swingarm off the back. Maybe you want 1kw, 2kw. . . .

http://www.qs-motor.com/product/qs2000w-bldc-mid-drive-motor-assembly-kits-for-electric-motorcycle/

None. Worst possible platform for a motorized bike. Small, uncomfortable, no suspension, and heavy once you add motorized components.

Ah the main thing i forgot to mention, this is a commuter bike and for it to be street legal in my area it has to be a max of 750 watts and limited to 20mph however i would like to be able to turn the limiter up to perhaps 30mph if i get the chance to ride it in an enviornment where i can really put it through its paces.
But i live in a town that is somewhat hilly, not a mountain town by any means(central il, usa)
Im more interested in throttling than pedal assist but i believe it has to have functioning pedals to be a street legal pedalec

flat tire said:

None. Worst possible platform for a motorized bike. Small, uncomfortable, no suspension, and heavy once you add motorized components.

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Im adding a suspension fork to the front (mentioned in first post) , possibly a banana saddle for the seat to make it a more comfortable ride.
Maybe ill raise the handle bars too

www.goldenmotor.com is in China
www.goldenmotor.ca is in Canada an authorized dealer of HQ in China

As far as street legal, the beat cop doesnt know the difference between a 250W, 500W, 1000W motor so its not an issue as long as you dont be going around pissing people off and speeding on your ebike. Be a courteous and responsible ebike owner. A fat 400lb rider should not have the same watt requirement as a 100lb crack head.

If i really want a mid drive what are my options for changing to a multi geared setup besides the obvious throw the whole bike out and get a new one :lol:
(Still stretching the frame,mounting the derailer?)
My hope is that a mid drive even on a single gear setup will do what i want to do (zip around town at 20mph, climb hills at a decent pace)

Options would be a rear hub that is an IGH Internal Geared Hub from Shimano, Nuvinci and the like.
If you can find one in the rear dropout width of your BMX.

Then mounting the mid drive.
https://em3ev.com/shop/bafang-36v-250-500w-bbs02-kit/

Article by SpinningMagnets
https://www.electricbike.com/bafang-bbso2-750w-mid-drive/

I thought about converting a BMX at one point, but most of the used bikes I looked at had a single piece (Ashtabula) crank, which was a non-starter for mid-drive without custom adapters. Can't tell by the pic, but maybe yours has a normal three piece crank and bottom bracket?

This guy used a big hub motor so the cranks weren't an issue:
https://www.youtube.com/watch?v=GA6HvPu6OSY

JIMONAH said:

My hope is that a mid drive even on a single gear setup will do what i want to do (zip around town at 20mph, climb hills at a decent pace)

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There is no point to it at all, if you don't have multiple gear ratios. It will only get you inefficiency and accelerated wear and tear, plus stupidly wide cranks that make you pedal like a duck. Get a geared rear hub motor that is spaced 110mm, if you can.

Your bike frame is made of aluminum, and is thick and stiff with especially short rear stays. It's almost uniquely bad in terms of its prospects for being respaced for a wider hub. You're gonna screw it up if you widen it significantly. And if you don't, you definitely don't have room for multiple gears.

I once put a relatively narrow 5-speed internal gear hub into a buddy's BMX bike. But it wasn't as bad a candidate for bending to a wider spacing as yours is.

Check http://ebikes.ca for their folding bike rear motors; one of them may be the right width for your bike.

If tha'ts not an option, you can convert a front hubmotor to a rear.

Take an old rear hub and cut the threaded end and flange off, and drill out some of the spoke holes, and remove the bearing cup. Take the right side cover off the motor, then center the flange on the cover, and drill matching holes in it. Bolt the flange to the cover. Reinstall cover. Install freewheel from your bike onto this.

Now you have a narrow rear motor.

If you look thru my threads there's one for doing this, something like "converting a front hubmotor to rear".


If you want multiple gears, that's probably going to need a new bike. Spreading the rear enough for a "normal" width hub and cluster is difficult to do evenly, and even if you get it even, unless the frame is steel (which I don't think yours is), it may crack at the BB shell (maybe not now, but later). Even a steel frame isn't meant to be bent that much.

A 3-speed IGH wheel would give you at least some gearing changes, but it may not be enough for what you want it to do (depending on what that is, exactly).


You *could* lengthen the bike *and* get multiple gears by bolting (or welding, if it's steel) on the rear end of a regular (or folding) bike to this one (see threads like Dogman's Bouncing Betty" and my "bolt together semi-recumbent bike" for examples).

Thsi would also give you the option of a Stokemonkey (or similar) setup for a middrive.


FWIW, there's not much int eh way of useful suspension in 20" forks.

There is the option of adding 20"-spaced dropouts to a good 26" fork (that does have useful suspension), where the original dropouts would hang down near the ground, and the new ones would be added 3" above those, clamped to the lowers tubes. (or welded if they're steel). I did that to get something sort-of useful out of the crappy choices I had for my first custom-built bike.

A geared hub and mid drive is an option.

Shimano Nexus 7 with a BBS02 would go alright on a BMX frame.

That hub will fit a dropout as narrow as 127mm though, and a BMX is 110mm so you need to spread it 17mm.

I found a three speed IGH that is only spaced to 120 mm, so i would only have to spread 1 cm.
Will a 3 speed igh be enough to make a bbs02 efficient? And i just did the magnet test and it didnt stick to the bike so i believe its aluminum so will 1 cm be too much for the frame to handle?

JIMONAH said:

And for the record i have no qualms about motorizing this bike, i just didnt want to have to spread the dropout out of laziness and fear of not having the right tools or doing it wrong

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I was so lazy with my last frame, that I looked around my garage, and ended up putting my dropouts on either side of the exterior o of my bench vise and then opened the vise slowly. It actually worked out great, since I could use the jaws to take my measurements, and move around to the front of the frame to make small alignment adjustments. That was a steel frame though.

10mm inst really much.

Pretty sure I would have spread my dropouts on my MTB at least 5mm and that was a 135mm motor going in a 135mm dropout. The extra width was required to fit in enough spacers for the chain to clear the frame at the dropout in the highest gear.

That's a 29" bike though so the chain and seat stays are a fair bit longer and have more flex. Not sure about a BMX.

Also, what bottom bracket does that bike have?

If its an American style BMX then you will need an adaptor to fit a Bafang mid drive in there.

Something like this

https://lunacycle.com/american-style-eccentric-bb-to-bsa-adapter/

Now that you said commute on it, unless you are under five feet tall, you really need a different bike. Don't commute on a bmx, unless you are talking about a 2 mile round trip or something very short.

Best possible option on the cheap, a 7 speed beach cruiser. Huffy panama jack, or Schwinn. After that, a used 7 speed mtb like a trek 820.


Mo money, hard to beat electra cruisers.


Put an almost legal rear motor kit on it, 48v, with a display. In town if you must, run it on slower power level. But if you just throttle a 1000w kit, able to go 27 mph, you can simply ride inconspicuously when needed, and let it rip when out of the town center.

lionman said:

Also, what bottom bracket does that bike have?

If its an American style BMX :wink: then you will need an adaptor to fit a Bafang mid drive in there.

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The bike has a one-piece crank, which only fits through a large diameter shell like American or Swedish. And that one ain't Swedish.

Another thing the OP might not be thinking about is chainline. The chainline of a BMX bike is much narrower than the chainline of a crank drive like BBS02 or TSDZ2. And since it's a single speed, it's more dependent on correct chainline than a derailleur bike.

Thanks guys ive reconsidered my options, and im considering saving for a super 73 z1 and riding it stock untill i can afford/feel confident in my ability to upgrade it, thinking about turning a z1 into a 2wd dual hub motor bike.

JIMONAH said:

Ah the main thing i forgot to mention, this is a commuter bike and for it to be street legal in my area it has to be a max of 750 watts and limited to 20mph however i would like to be able to turn the limiter up to perhaps 30mph if i get the chance to ride it in an enviornment where i can really put it through its paces.

Click to expand...

You'll need more than 750w (about twice that) to do 30MPH.