Motor Wheel

Motor wheels are challenging. There are heavy, there transfer a lot of force and demand a good build. Most of the time I build a motor wheel is for a reperation. I often changed everything because sincerly... There are build very poorly.

Motor Hub :

There are a lot of motor hub around and it is difficult to source what they are. So you should measure it yourself. For this tast you need special tools like big compas ? and round compas. Specialy drill wood thing.

Hub holes are oversized, often more than 3 mm. You will need special spokes.

You often does not know what is the entrax of the hub. 135 mm, 140, 145, everything is possible and it is also related to the frame. Sometimes you try to guess the best you can.

Rim :

They are often underweighted for the task. I advise The Andra Series from Ryde - you can drill them - or the Utilities Series from DT Swiss - No drill with Eyelets. The rim needs to be strong and that often means heavy - 700 to 1000 g for a 28". Weight does not really matter, you are on E-bike anyway.

I would never go below 600 g for a 28". If I find the rim to light I will add washers to strengthen it.

Spokes :

I mostly use spoke with 2.3 mm or 2.6 mm J-bend ankle. Sapim Strong 2.3 - 2 mm, E-Strong 2.6 - 2.3 mm, DT Alpine III 2,3 - 1.8 - 2 mm. You might also use DT Champion or Sapim Leader 2.3 mm. They go be as small as 70 mm on a 20" wheel.

Nipples : 

Definitely brass nipple. Sapim Oversized, reduction, 13G from Pillar, you often have to use dedicated nipple to the rim. See the chapter on "All those nipple and rims" for more details.

Avoid 13G nipple not reduce, the paroi is thin.

You might drill to use the 13G. So Andra Series is nice. Eylet does not permit to drill.

Crosses :

That's an interesting topic. It will be good to use the calculator from Grin technology at this point.

You will need to check the angle of entry of the spoke in the rim. With a round shaped spoke like the Polyax from Sapim you can go up to 12° maximum - 78° on Grin. With a rim with oriented holes, you can go up to 25° - 65° on Grin. 

You will see that you will rarely cross more than 2. And definitely go with a radial build with a small wheel.

Spokes head on one side. Careful of the disc space. Improve tension by testing the side.

Force :

Let's talk about physics. Radial no force. No power transmission, no brake.