TOO much torque on 20in Uber Bafang front wheel

[dialadrone]

Hey y'all. I My usual ebike is an old mountain bike i threw together with 26in rear wheel drive. Considering how little I pedal an ebike I figured why not make a much smaller one so its easier to throw in the car for little trips. I slapped together a pretty odd little bike out of an old Schwinn bmx. I laced one of those banfang hubs from a decommissioned uber/jump bike into a front 20inch bmx wheel.

ts pretty fun to ride, but the small front wheel has so much torque that it wants to slide out when starting from a stop and giving any kind of throttle on a turn is a terrible idea.

Overall the build feels a bit too sketchy to ride regularly due to the front wheel skidding before it grabs. Is there anything I can do to lower the torque while maintaining my top speed? I'm running a 48v battery/controller and am wondering if downsizing to a 36v controller/battery would make the low end a little safer? Is this build doomed sine the hub was meant for a larger wheel? Should I just bite the bullet and try to convert the front wheel to a rear since its a single speed? Any tips are appreciated.

 

[dogman dan]

Lower the wattage but keep the voltage the same should work, to the point where the wattage itself limits. 500w should still get you around 20 mph.

But I'd just learn to ride front hub better. I had similar trouble with my very first e bike, but later on ran 3000 plus watts without a lot of issues. It's a matter of learning to ease into the throttle, get rolling, then romp it on. It won't take all that long for you to get used to some spin taking off, and know how much throttle you can give in a corner, and when to avoid a front wheel power drift. You will also learn to lean into the bars on those starts a bit more.

Soon you will not notice this anymore, unless you have done something to really upset the geometry of the bike.

 

[Chalo]

BMX bikes aren't made to fit adults. It's foreseeable that weight distribution will be wrong when they're pressed into service as clown bikes.

If you don't pedal, and you only want something compact, you might as well get a kick scooter with 20 inch wheels and put the motor on whichever end you prefer.

 

[dialadrone]

I acually put the wheel in the rear to see if it would handle better today and it was terrifying! Total wheelie machine! so much for the idea of welding part of a rear hub on so I could attach a free wheel.

dogman: thanks for the info on wattage, after changing the handlebar angle to distribute my weight forward a little more its not as freaky but the throttle is still so sensitive that its hard not to send that wheel skidding at first.

Chalo: The kick scooter idea is cool but i've had this old 70s schwinn bmx collecting spider webs in the yard for years so i'm gonna stick with it.

half the fun for me is making something out of the junk I've got lying around, so far i'm in the hole about 20 bucks for the spokes. Might just have to ride it as is or hunt down a 36v battery/lower watt controller to slow it down. My current controller came from a free pile and doesn't say how many watts it is but i assume it is high because this thing flys.

 

[Chalo]

I acually put the wheel in the rear to see if it would handle better today and it was terrifying! Total wheelie machine!

So you do have an intractable weight distribution problem. That's one of the drawbacks of putting an adult on a child's bike.

If the seatpost has separate guts on the top, try turning them around to mount in front of the post, and slide the seat forward before tightening it down. Tilt the handlebars forward to buy back a little more room in the cockpit. You can also try attaching the battery to the handlebars. All these things will increases the fraction of weight on the front wheel, which will improve traction.

If you're using a controller rated more than 22A or 500W nominal, you're likely to cook that motor in pretty short order.

 

[dialadrone]

I acually put the wheel in the rear to see if it would handle better today and it was terrifying! Total wheelie machine!

So you do have an intractable weight distribution problem. That's one of the drawbacks of putting an adult on a child's bike.

All solid points! I did some seat rearranging and got it to where it rides fairly comfortably but alas another issue has arose! I’m going to start a separate thread to address the new issue rather than lump the together. Ty for the help!
If the seatpost has separate guts on the top, try turning them around to mount in front of the post, and slide the seat forward before tightening it down. Tilt the handlebars forward to buy back a little more room in the cockpit. You can also try attaching the battery to the handlebars. All these things will increases the fraction of weight on the front wheel, which will improve traction.

If you're using a controller rated more than 22A or 500W nominal, you're likely to cook that motor in pretty short order.