Spoke length help

[James28]

I need to fit a 26" rim to a rear bafang hub motor (RM G020.250.DC 10) it takes a cassette if it makes a difference.

Ive rebuilt quite a few wheels before just measuring off old spokes but never had to calculate my own.


Is there anything different to building a hub motor wheel?

Would a 1 cross lace be sufficient (bike is used for commuting on ok condition roads, no suspension) i think 2 cross would make the nipple enter the rim at too much of an angle.

Specs for this motor seem to be 13g but the standard seems to be 12g. I personally dont think this is a big deal but i'd be interested to hear otherwise.

The ERD of the rim is 537mm
(Drive side is right hand side)

1 cross lace
Left 202mm
Right 201mm

2 cross lace
Left 218mm
Right 217mm

These are what i've come up with, i'd appreciate if someone could double check me. Ive added the dimensions for my motor

 

[Nealh]

1x lace you are correct because of the nipple angle.
Using grin calc I get left 200.7mm & right 201.7mm.
What rim width ?
I use 14g Sapim strongs on all my motor hubs as thye have more give then 12/13g.
Also if within 1mm I use all the same length as well so would go with 201mm.

Did you factor in the 5.6mm offset to the rhs which should be he dish factor so rhs spokes should always be a tad longer.

 

[James28]

Thank you very much, looks like im on the money with the length (I did round to the nearest 1mm).

Rim width is 24mm overall and 19mm internal

I think i'll go for the best fit for the spoke holes in the hub regarding the gauge.

 

[James28]

I halved the flange to flange, added 5.6 to the left to give 26.85, took 5.6 off the right side to get 15.65. Which did seem like quite a big difference to me.

It looks like i have my left and right mixed up, the calculator im using uses different left and right for the front and back wheels. I used the calculator for the front and figured it wouldn't make any difference for measurments

 

[Sturmey]

Specs for this motor seem to be 13g but the standard seems to be 12g. I personally dont think this is a big deal but i'd be interested to hear otherwise.

Dont use 12g spokes (imo) as I had to drill the rims spoke holes wider and in the direction of spokes when replacing rims lately. (The wheels were originally built with 12g spokes) Also this is not really possible with rims with eyelets so I used plain rims. 14g as suggested by Nealh is normally a good choice.

 

[James28]

I did wonder at what point spokes became too big for rim drillings. 12/13 seems pretty massive for a bicycle (imo). Pro's can put far more through a wheel than the 400watts im putting though mine with fewer and thinner spokes.

The sapim strongs are 13 gauge at the j bend and 14 thoughout the length of the spoke which is ideal for filling the holes in the hub flanges properly.

 

[Barnsleyrob]

My Pinnacle has the same motor on a 27.5” rim and it uses 12 g spokes. Not very good ones in my case !

I don’t want to hijack your thread, but what are you using as a speed sensor ?

 

[Nealh]

12g spokes tend to break as they aren't very flexible, the 14g sapim strongs are very good and as said they are only 13g at the bend .

 

[James28]

Im using a kt controller and a kt lcd 3, i believe it calculates speed from inputing the number of poles ( of the motor) x the gear reduction and the wheel size. Its basically all built in.