2WD (Two-Wheel Drive) FAQ

[MacgyverHK]

100 km/h with front wheel drive on a bike is not a practicable setup. The wheel will spin and skitter around at any speed that bikes are good at. Don't bother.

If you want better, like closer to 30 mph speed, use 2WD. That spreads out torque and heat, and increases power much more than torque. If you want big, like 60 mph speed, only rear wheel drive will to do that reliably.

Bikes don't go much faster than 30 mph without misbehavior. You can work around that, but not without making handling qualities suffer at bicycle speeds.

Good point. I really am not interested in speeds above 45 but i am interested in building a front and rear system that can work together.

 

[MacgyverHK]

I am open to a lesser geared hub motor as an option.
Interested in my 2WD setup choices.

Good point. I really am not interested in speeds above 45 but i am interested in building a front and rear system that can work together.

 

[MacgyverHK]

"Hub motors don't really have a voltage"

Hello Chalo

What do you mean by this? Please school me.
Can i run a 48v Brushless geared hub motor on 72v?

I was thinking originally of using the front motor as a torque boost and extra grip off road where the speeds are much slower, like hill climbing.

If my rear motor has I higher top speed, wouldn't the freewheel just go with it if I am not applying power to it?

 

[scianiac]

You can technically run any motor at any voltage until you reach the breakdown voltage of the windings which is very high. The real number you need to look at it is not the motor's voltage rating which is just a made up recommendation but the motor's Kv which tells you how fast the motor will spin unloaded at a given voltage. Then you can find what motor will work based on your target speed and voltage keeping in mind at that RPM the motor will make zero torque so a value less than that is the real speed you need. And spinning the motor way beyond or below it's designed speed will result in poor efficiency.

The thing to watch out for is if the front motor doesn't have a freewheel like with a DD motor and the motor Kv is too low the back voltage from driving it too fast will damage the controller. If it does have a freewheel like with most geared motors then it won't matter.

I still think with the bike you posted a picture of this a front motor will offer little advantage and lots of disadvantages that will probably outweigh the advantages. If you need more traction all you need is to put on some more aggressive tires at a lower tire pressure, yes this has some on road downsides but there are tradeoffs with everything and those tradeoffs may be easier to make than the ones from the 2nd motor. Your rear suspension is already pretty poor offroad with that much unsprung mass so why you would want to make the front suspension worse too. Just an example of one of the front motor downsides.

 

[MacgyverHK]

Thank you for your response

 

[motomech]

I've built several 2 WD bikes and it's only worth the extra parts and complexity, w/ low to mid powered motors. If the rear motor system has any power above 1000 watts or so, brisk acelleration will unload the frt. wheel to the point where it will spin on anything more slick than dry pavement.

 

[MacgyverHK]

I've built several 2 WD bikes and it's only worth the extra parts and complexity, w/ low to mid powered motors. If the rear motor system has any power above 1000 watts or so, brisk acelleration will unload the frt. wheel to the point where it will spin on anything more slick than dry pavement.

How are about a light low power geared hub motor just for off-road traction at lower speeds?

 

[Chalo]

I've built several 2 WD bikes and it's only worth the extra parts and complexity, w/ low to mid powered motors. If the rear motor system has any power above 1000 watts or so, brisk acelleration will unload the frt. wheel to the point where it will spin on anything more slick than dry pavement.

If only car drivers were so conscientious as to reject vehicles that spun their wheels when you get too deep in the throttle, what a wonderful world it would be.

I find front wheelspin on a front drive to be very tolerable, because unlike front skids on an unpowered wheel, the spinning wheel keeps pulling the front of the bike in the desired direction.

Data point: My 2WD bike has about 1000W (electrical) in the front wheel and about 1500W in the rear wheel. The front motor has a configurable display, and all I had to do to mitigate front wheelspin was to set a slow start throttle ramp for the front wheel.