Which motor to choose for a foldable Dahon ?

[marc.bastien]

Hi, I am looking to fit a hub motor to my Dahon muP24 on its front fork.  The inside width of the front fork is 76 mm.  Which motor would fit? The mini seems to wide and not sure about the 901 diagrams! An someone helpout please?

[Bikemad]

It might be very difficult to find a hub-motor that is narrow enough for that gap. Most front forks are usually between 90-100mm spacing. It seems that Dahon must be using a much narrower hub so that it is more compact when the bike is folded.

If the forks are steel, you might be able to spread them to allow a wider axle to be used, but if they're aluminium it's not even worth considering.

The best option might be to find a set of standard steel forks to fit your frame, but with a wider axle width to allow the hub-motor to be fitted.

I have attached a diagram of the HBS front hub showing some of the dimensions, just to give you an idea of their size.

Alan
 

[marc.bastien]

I checked on the Dahon website and the fork is made of aluminium allow (U7). So that's it for the front fork. The rear wheel includes an internal 3 gears and external 8 gears making it useless to consider changing the wheel for a hub motor.   
I had seen a Brompton folding bike with a Nano hub motor which requires a fork spacing of 74 mm. I couldn't find a kit for sale. 
I will now turn my attention to my 700C (28 inches) Devinci hybrid where the forks are standard sizes (front approx. 100mm and rear approx. 135 mm).
I wish to thank you Alan for your quick response. I am new to electric bikes and conversion kits. If I could find one that would fit my bike and carry me (200 pounds) for at least 30km at max 32km/hr, I could commute the 40 km in then 40 km back from work! 

[SydneyCommuter]

Mark
Couple of things to consider
The direct drive motor you need to keep under power for the entire trip. There is back emf resistance when it free wheels with power off.  So you need the full 40km range for that. The pi with 48v battery is about 30 range. The old 36v lithium 16 ah battery did about 50kms not sure what the new 12ah lipo battery is getting but speed you should get around that 30kmh the 48 does about 36kmh.
If you want to peddle unassisted any distance you need a geared motor that free wheels without power and down hills, they are also lighter and less power so may get you the range from std battery. Not sure top speed, there are posts about the 902 mini motor by way of example.
If your still going for a couple more weeks I'm building a dual mini so will be able to comment from experience then, others may give you a heads up now.

Good luck