Managed to break 3 spokes on my BPM rear hub. Measured them to be 200mm but not quite sure. Anyone know the correct length? I will say they do seem a bit long as all the spokes have an awful bend where they attach to the nipple.

No knowledge of lacing so just an opinion that may be wrong

The length depends on the ERD of the rim and the lacing pattern. Every type of rim has a different ERD. We can't tell you the ideal spoke length without those two pieces of information.

you can use the spoke calculator here:

http://www.ebikes.ca/tools/spoke-calc.html

 

select Bafang BPM as hub, 26" rim as rim, 1-cross as pattern,

 

We have spares if you need some.

 

edit:

our spoke length 200mm.

Edited November 23, 20178 yr by Woosh

you can use the spoke calculator here:

http://www.ebikes.ca/tools/spoke-calc.html

 

select Bafang BPM as hub, 26" rim as rim, 1-cross as pattern,

spoke length 190mm.

 

We have spares if you need some.

Is that the best pattern? Only asking because the spokes have snapped the tread off and wondered if it was because of the angle they meet the nipples. I don't mind paying to have it relaced if it would relieve that stress on them.

Is that the best pattern? Only asking because the spokes have snapped the tread off and wondered if it was because of the angle they meet the nipples. I don't mind paying to have it relaced if it would relieve that stress on them.

 

I have left the office, so couldn't check.

I think we use 2-cross pattern.

The problem is usually spoke tension. They need to be even on all 36, firm but not too tight.

I know nothing about lacing patterns . What is this ? Would there be a better one? How much are spokes and nipples? Are brass ones the best?

Anthony, I'll send you 3 spokes tomorrow.

Is that the best pattern? Only asking because the spokes have snapped the tread off and wondered if it was because of the angle they meet the nipples. I don't mind paying to have it relaced if it would relieve that stress on them.

Use 14g spokes instead of 13g. You can then choose 1 cross or 2 cross, though I think 1 cross might be better. You still need the rim ERD to calculate the spoke length.

 

If your spoke length is 200mm and you presently have a 2 cross pattern and the spoke length is correct, your ERD is 516mm.

Use 14g spokes instead of 13g. You can then choose 1 cross or 2 cross, though I think 1 cross might be better. You still need the rim ERD to calculate the spoke length.

What's the difference in patterns? How do I find the edr?

You get the ERD from the manufacturer or listing, but you need to know which rim it is. Alternatively, you can measure it when unspoked or make yourself a massive caliper gauge. You measure the inside diameter of the rim in two directions, take the average and then add on 3mm to get an approximation of the ERD.

 

You can make a caliper gauge out of thee lengths of wood in the shape of an A. Bang a nail or screw in the top and one in the side. The cross piece needs to overlap. Position the two feet of the A inside the rim and clamp the other cross-piece end with mole-grips. Check that the feet make a nice sliding fit on the rim, then measure the distance between them with a tape measure, then add on 3mm to get the ERD.

Anthony, I'll send you 3 spokes tomorrow.

thanks, ride it every day so kinda lost without the bike now.

The lacing of your wheel looks kind of iffy to me, especially the angle at the nipple is indeed very strange. Where did they break, there?

 

My Mxus is laced in 1 cross in a 26" with 12g or 13g spokes (can't mesure just now) but the angle at the hub is decent. I am going to lace it into a 28" rim 2 cross and 14g spokes.

The lacing of your wheel looks kind of iffy to me, especially the angle at the nipple is indeed very strange. Where did they break, there?

 

My Mxus is laced in 1 cross in a 26" with 12g or 13g spokes (can't mesure just now) but the angle at the hub is decent. I am going to lace it into a 28" rim 2 cross and 14g spokes.

yeah, snapped right at the treaded part. would 1 cross reduce the angle?

I know nothing about lacing patterns . What is this ? Would there be a better one? How much are spokes and nipples? Are brass ones the best?

 

2 cross in a 26" rim with a 180mm bpm isn't ideal for nipple angle.

A 2 cross lace, the angle at the nipple is a bit stressed. A 1 cross lace will straighten the nipple entry though needs complete rebuild and new shorter spokes.

think i'll plan for a rebuild in the near future. ill get it up and running with replacement spokes. have to find out spoke length and get some ordered.

Remove a good spoke and simply measure the length from end to middle of the elbows bend.

I think spoke length is measured to inside of the elbow, which is different from above by only 1mm typically.

 

Your picture looks like 2 cross to me, large hubs are often 1 cross.

 

You can see the difference if you play around with the spoke calculator mentioned above. If you put in the relevant data you should be able to confirm your 200mm spoke length. This is a good start for understanding what is needed to re-lace a wheel. Ideally a spoke should be just shy of protruding from the nipple, (not always possible).

 

At least with a large hub you won't have to remove the cassette (or freewheel) to replace spokes. Maybe you need to keep a spare spoke handy in case of further problems? One broken spoke can stress the next and so on. Check spoke tension without tools by squeezing two together by hand between cross and rim and comparing around the rim, and comparing with a known good rim with similar pattern etc. You're going to need to do this when you replace your broken spokes. Remember that spoke tension on a dished wheel differs from drive side to non-drive side slightly, (or disc side to non-disc side at the front, possibly).

 

If you do re-lace take lots of pics and allow quite a bit of time, if it's your first. Read Sheldon Brown's guide (as you progress), and allow for the fact that electric motor hubs are sometimes laced with spokes leaving on one side of spoking flange instead of alternating, witness marks on the hub will give a clue after disassembly. These details can be seen on the spoke calc graphics quite well, I think. My opinion is wheel building whilst a challenge can be quite rewarding.

 

Are 2mm = 14g spokes thick enough, for these hubs? Any opinions, either way, anybody?

Sapim strong are 2mm spokes except at the bend where they are 2.3mm, they would be my first choice.

 

Velomobile wheels are often built with aero spokes, so even less than 2mm in the blade section.