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Spoke length help

By MrMez - Posted on 30 October 2014

NB: Originally posted elsewhere on the Global Riders Network and appears via syndication.

Building a new set of wheels, and I need to double check spoke lengths...

Using DT hubs, so the DT calc comes in handy.

Rim: ERD 522
Front: DT 350 straight pull, centre lock, 15mm
Rear: As above, 142x12
Hidden/Internal nipples.
From there, all the numbers should be correct.

What I get:

(incl. Corrections)
272 mm
274 mm

(incl. Corrections)
274 mm
273 mm

-With only 2mm difference between longest and shortest, I should be ok with 274mm for everything?
-Anything I've missed or incorrect assumptions?



I did try that one.

Doesn't give any info about nipple orientation and length, but It kinda adds up listing the spokes at ~24mm shorter, which is about what you'd need to run external.

Surprisingly, the DT calc gives the same spoke length for 1, 2 or 3 cross, unlike ProWheelBuilder.

I'm thinking of going through the same exercise. I've been looking at the spoke calculator on the Sapim site'as I'll probably use their CX-Ray spokes.

This site requires you to input physical measurements based on their guide, and makes you select the number of crossings for both the gear and non-gear side.

It just strikes me as being a lot more thorough in what it asks of you, so you hsould get a better result based on more information and fewer assumptions (eg, not asking for the number of crossings doesn;t inspire me with confidence). Of course, garbage in garbage out, so measure twice and enter credit card details only once. Eye-wink

I have a heap of unused Cx rays spokes. Left me know what length you need and if I've got the right size it could save you

Yeah also settled on cx-rays. Best combination of price and performance.
I'm using straight pull, assume you have j bend.
As usual I did inquire with my lbs, but $10 per spoke and nipple to supply only is a bit ridiculous.
Online I can get them literally half price including paid postage. Anyway... More to the point, with a set of enve wheels, what could I possibly be upgrading to???

Wow. What a joke. That's $560 just for spokes. Another $100 and I could have an entire wheelset from the rim manufacturer or I could buy the spokes and the wheel building jig and still be in front before labour.

The Australian distributor's industry tax again.

I'll work out the lengths tonight and PM you.

The suppliers of sapims are the problems. If you buy online by spares as the supplier won't just sell the lbs one or two - they need to get a set which the lbs is unlikely to do as they will get stuck with them.

Yes I've got the j

Just been doing my head in using all 3 calcs side by side, trying to get them to all agree, when I realised I'm making a massive mistake with spoke cross and straight pull hubs.

Straight pull hubs have an inherent spoke cross you can't change. Duh.
Thats why changing the cross number in the DT calc rendered no difference. DT obviously know their own hubs a little better.

What I can figure out...

ProWheelBuilder makes no adjustment for rim thickness and allows no nipple choice.
Sapim allows manual rim thickness, but no nipple choice. (Both assume ~14mm external nipple)
DT allows a choice of nipples and automatically adds ~3mm for rim thickness.

Adding 3mm for rim thickness and 9mm for internal nipples to the Sapim and PWB calc, gives the same numbers as DT.

Finally, the magic numbers are 272-274mm. Safe to just get 273 all round?

I'm not sure how the internal nipples will sit, but going short with your spokes and conventional nipples can leave the thread just shy of the nipple head. The underside of the nipple head has the highest concentration of stress in the assembly. Extending the spoke thread to the top of the nipple reduces the resultant tensile stress at the critical nipple rim interface.

It's not a huge difference but significant at or near the point of failure.

When life is wheels. Ommmmmmmmmmmmmmmmmmmmmmmmmmm. Oommmmmmmmmmmmmmmmm.

Just checked: CX-Ray spokes come in 2mm even increments. So it will be 272 OR 274mm?

Also, for nipples internal to the rim, are you adding or subtracting from your spoke lengths? I'd have thought you'd need to add (sorry if i havent read that right, it's Friday afternoon of a busy week and my brain is fried).

True about extra thread providing extra strength. I'll sleep on it, but not sure the extra 1mm is a concern, especially since the lengths are rounded up.

I've found straight pull CX-Rays in 1mm increments. ProWheelBuilder seems to have the best price and good ground shipping within USA.

As best as I can guesstimate from looking at a cross section rim, thickness by the spoke hole is ~3mm, which needs to be added to the spoke length.
Adding 9mm on top of that for internal nipples leads to the the exact same length in both the DT calc and the sapim, where you can enter it manually.

Yeah double check everything I ended up having to do a four cross 32 spoke build because I went too long. Even CX-Ray spokes don't last that long with such a stupid pattern, cracked a bunch at the bend whereas the ones on my DH bike have been flawless.

Bugger, should have looked at internal nipples with washers.
Surprised to hear 4 cross ended up breaking spokes.

did some reading a while back on wheel building by a guy named Roger Musson. He's quite the builder apparently, though he typically uses standard hubs and sticks to what he knows.

Anyway, his book says to calculate the Effective Rim Diameter "ERD" for EVERY wheel that you build, as the wheel manufacturers aren't exactly accurate in production, so what they send with the literature for the rim may not be anywhere near accurate enough for your build. His method is to cut 2 spokes to 200mm length, then thread a nipple on one so it's flush and crimp it so it can't move. Then tape some elastic on between the two and thread through the rim, then thread the other nipple on. You measure between the ends of the spokes and then add 400mm to the length to get the ERD.

He does say that straight pull hubs aren't something that he does a lot of due to the number of variables that change between every sort, but if you can work out the ERD at least you have a starting point for buying your spokes. Millimetres of accuracy make a big difference in wheel building and can make the wheel serviceable in the future. Too short and you'll get breakage due to stress points, too long and you'll be unable to correct any truing issues.

Thanks for the info.
Sounds like a lot of work Sticking out tongue

Ordered everything over the weekend, so just need to wait and see.
The rims are (what I believe top quality) hand made carbon. Being moulded, the ERD should be identical for every rim, unlike a possible inaccuracy between calculated and measured ERD with a rolled and welded alu.

Using 3 different calcs along with DT's own gives me a certain degree of confidence. Once I got them all to agree of course Eye-wink

Noticed today that pretty much every decent Shimano factory built wheel is straight pull. XT, XTR even dura ace road. But you can't find a Shimano straight pull hub by itself anywhere.

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