Lacing Bafang hub motor

[fitek]

Hey folks, I got a Bafang front hub motor and would like to lace it in a 20" wheel.

The trouble is I have never laced up a wheel or had it done for me.

If anyone knows a place where I can get it done for a reasonable price in the SF Bay Area let me know. If it is ridiculously easy I'd try it myself but if its less than a hundred bucks I'm tempted to just let someone else deal with it.

What else do I need to know? Type of spokes, pattern?

 

[Zoot Katz]

Wheel building requires a "touch" that isn't hard to develop after a few wheels.

Here's a decent article on building a wheel into a Bafang front hub.
http://www.pedelecs.co.uk/forum/tec...ld-suzhou-bafang-hub-motor-ezee-torq-1-a.html

He's using a 700C rim for which you can find the ERD (Effective Rim Diameter) and subtract the difference in the ERD of your rim to arrive at the proper spoke length for a two cross lacing pattern. Considering the smaller diameter 20" wheel you'll probably have to go with a one cross or radial spoke pattern so those numbers end up useless to you. The hardest part will be calculating the proper spoke length since there's not yet a data base including the pertinent measurements of common hub motors.

If the rim must be drilled to accommodate a larger nipple then you'll want to pay attention to the angle of the spokes when you enlarge the holes.
As always, Sheldon has the answer:http://www.sheldonbrown.com/wheelbuild.html

 

[Rassy]

I got my Bafangs from JohnRobHolmes and he laced one of them into a nice 20" dual wall rim with a one cross pattern. He would probably be able to provide you with the correct spoke length. I relaced a couple of my WE BD36's into 20" rims a while back. Since a 20" rim was one of their options I just purchased the rim and spokes from them. The lacing wasn't too hard, you just have to go slow and pay attention to avoid do overs. Good luck.

 

[dnmun]

ask holmes, he is the authority on wheelbuilding.

danscomp sells the 12G spokes too if you wanna do that and the bike shops can calculate the length too. the bafgang pdf is in one of knuckles threads too.

i am interested too, also thinking of building a 20" for an actionbent, 406mm that is.

make sure you get 36 hole rims since there are lotta 40 hole 20" rims for bmx bikes.

 

[drewjet]

A good lacing instruction tutorial.

http://sheldonbrown.com/wheelbuild.html

I used it and it came out great on my first try.

 

[fitek]

I got a rim, no spokes yet, but I'm wondering what length to order. The three shops I went to weren't any help there. Is it in Knuckle's pdf? I have a pdf of the hub dimensions from keywin.

 

[JS Tyro]

Search the web for a spoke length calculator. You'll have to take a few measurements off the motor hub to use them.

 

[johnrobholmes]

What is your rim ERD? I have the hub read in calc right now.


Just laced a bafang into a 20" for a friend this week. Actually did two builds for customers too. My buddy on 18s lipo hits a solid 22 to 25mph on the flats. Didn't get a chance to hit a speed trap or install a speedo on his bike, but it had great punch during acceleration.

 

[docnjoj]

Yep John! I just got mine and it looks really fine. Now I just need the new trike to show up so I can use it. This is my first "bought" wheel as usually I lace them myself and then get my LBS to true it. I'm afraid I just got spoiled by the new one! Thanks John!
otherDoc

 

[fitek]

I suppose I need to buy a rim to get the ERD? I bought one locally (beefy looking double walled aluminum thing) but now that I look at it, the holes in the rim look like they are for 14ga spokes not 12ga.

Is a beefy wide rim necessary? I'd prefer to go with the thinnest highest pressure tire I can get away with.

-Peter

 

[fitek]

So I used spocalc.xls, which you can find on Google, and the Bafang PDF.

130mm for dL and dR which is the spoke hole diameter and 23mm for WL and WR, which is the distance from the center of the hub to the flange on either side (along the axis of the axle).

Wheel ERD is 405mm.

For 1 cross, I get 145mm, for 2 cross, 163mm.

I have found 143mm and 165mm spokes. Hmm. The 165mm ones are stainless rather than just steel and come with nipples.

I wonder, then, whether to go for slightly oversized or slightly undersized? I am leaning towards oversized, as they could be cut down in the worst case...

 

[vanilla ice]

Out of those two choices I'd go 143 for cross1. For a 20" cross2 might be too much angle, plus one or two mm short isn't going to hurt anything. If you go 14g you can get exact length cut from Dan's comp. Very reasonable pricing. I wasn't clear on whether you are going 12 or 14g tho. They don't cut 12.

 

[fitek]

I called Danscomp and they said they could not cut the spokes shorter than 185mm. I am going for 14ga, I have a rim with 14ga spoke holes.

 

[ElectricEd]

I called Danscomp and they said they could not cut the spokes shorter than 185mm. I am going for 14ga, I have a rim with 14ga spoke holes.

Very sensible. 12g spokes are a pain due to the fact that there is very little elasticity in them. If one is a bit tight you can end up pulling the nipple through the wall of the rim. They also come loose more often for the same reason. Get good quality spokes such as DT, not the "Hoo-Flung-Dung" variety which are of questionable quality. Justin at ebikes.ca probably can make them to the length you need.

If you could post the hub dimensions I could do a backup calculation for you of the length required.
To do this I need:
Hub spoke hole size (2, 2.5, 3mm etc).
Hub spoke hole PCD (Pitch Circle Diameter).
Hub flange spacing (centre to center of flange).
Left and right flange offset from a center line drawn between the dropout spacing.
Number of spokes.
Pattern (as vanilla ice said, cross(1) is the max you should do for a 20" rim).
Effective Rim Diameter (of nipple seats).

 

[monster]

if you have several spoke sets lying around then you can probably make do with some combination of those. i laced a wheel with two different spoke lengths that combined made up for the fact that neither one fitted correctly by itself. you can make up a few mm + or - by swapping the spoke ends from outside to inside or visa-versa. most hub motor nipples have loads of travel on them which makes it easy. i can lace a wheel while watching the TV now. (assuming everything is nice and clean)

 

[docnjoj]

I second the 14 Ga. spokes. Either Swissdt or Danscomp or other high quality drawn or better yet forged spokes. Much easier to lace and I have never broken one even in the trike. Of course, letting someone like John Holmes do it really makes it quite pleasant for me! And he actually knows what he is doing. I to used to lace 'em while watching TV. Still not exactly fun!
otherDoc

 

[fitek]

I bought DT Swiss 165mm. We'll see how it turns out. Also stocked up on some other goodies...

 

[fitek]

Tried 2 cross with the 165mm, but they are at least 10mm too long. Too short for 3 cross.

150mm or so would be ideal, but where to get those... the search continues

 

[johnrobholmes]

I typically use 139mm for 1 cross and 395 erd. 2 cross is too severe of an angle at the eyelet IMO.

You will want 144mm for 1 cross and 159 for two cross, if your ERD is in fact 405

 

[fitek]

Thanks JohnRobHolmes, I found a local shop that will cut my existing spokes down. Will swing by tomorrow and try to find something that fits your numbers.

I measured the ID of the rims at 395-398mm (inaccurate measurement device, heh). The published ERD is 405 though. That's 10mm off, which is about what my spokes are off... so I'm thinking the published ERD is wrong.

 

[johnrobholmes]

The ERD is right where the nipple head should seat, so a few mm addition to the ID is about right. Building them is more of an art than science really, and very rarely does a wheel turn out perfect unless it has already been built before.

 

[fitek]

I got 13/14 guage spokes. They will be cut to 139mm for 1 cross.

We double checked the numbers using QBP's app. The ERD for the Alex DM24 20" is 395mm. Not sure where I got the wacko 405.

Spokes will be done Monday... will report back when done. Guess I'll unlace the bad ones and also swap in that metal gear I have.

I've now spent more than just getting the wheel from JohnRobHolmes but hey dudes, this is "fun" isn't it hehe

 

[johnrobholmes]

:lol: it cost me quite a bit in spokes and labor to figure out my first few hub motor builds too. Now I lace them so often I know the sizes by heart.

 

[fitek]

Lacing is all done, but what size axle is this and what is this thread??? I tried a bunch of nuts laying around in the shop and none fit. Guess I'll have to go to Orchard and then perhaps order from McMaster...

 

[johnrobholmes]

I don't know what it is, probably metric.