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Could anyone tell me the spokes I would need for a Crank Brothers enduro synthesis alloy rim for a 27.5 and a pro 4 disc hope hub 148 mm boost rear wheel 3 cross. I have built a few wheels and pro wheel builder said I would need 273.3(I rounded up to 274) for the left and 272 for the right but every other spoke was way to long so I tried 272 for both sides and every other spoke was way to long as well. I have checked my 3 cross lacing pattern multiple times and from what I can tell I am not doing anything wrong so I figure it has to be the spoke size.So if anyone could potentially point me in the right direction id appreciate it. ( i am using 15mm spoke nipples)

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If I measured the rim to be an actual ERD of 564 (the published number) with the nipples I was using, this is what my calculation would look like using the raw formula via Spocalc:

spocalc

From there I would choose 271 for my right length or 270 if that wasn't available, and 272 for my left or 271 if that wasn't available. The rouding down by those amounts is to compensate for spoke stretch and rim compression. Never round up.

Your problem could be occuring because published ERDs usually are based on 12mm nipples. Longer nipples typically have longer threaded sections, so they can make a spoke that would be perfect for 12mm instead bottom out on the threads with a longer nipple. This issue is real but a detail that gets left out of too much written work about wheelbuilding.

Cut to the chase and measure the ERD yourself. Take 2 spokes of known length, poke them into the rim 180 degrees apart, then take 2 of the nipples you're using and screw on the nipples until they're at the point you want to define as ideal thread engagement. With 12mm nipples, that usually means the tip of the spoke flush with the top of the nipple, but with longer ones you have to choose how you're going to define it yourself. Usually what I do is screw the spoke all the way in and then back it off two rotations or 1mm, which for most spokes is 9mm of thread engagement out of 10mm of thread on the spoke, or thereabouts. Take your vernier caliper and pull the J-bends tight together with the jaws, then take the measurement of the caliper and add it to two times the spoke length. That is a method for measuring ERD that is superior to all commercial systems because it automatically accounts for any quirks of the nipple you're using, which is done virtually or not at all with other systems such as the Wheelsmith tool.

This measurement will likely give you a number that accounts for your long nipples in a way the published number isn't. You will probably plug it in to a spoke calculator and see what's going on immediately.

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  • Curious - I'd happily round up if to 272 it were 271.9. I'd even go up 0.2mm or more if it were double-rim construction, and if the spoke ends up poking through the nipple I'd file it flush with a dremel or a hand file. – Criggie Feb 6 at 8:36
  • A DT Swiss Alpine III spoke stretches around 0.65 mm at optimal tension if you have measured the ERD using untensioned spokes. 12mm nipples allow typical spokes to protrude around 1.4mm from the nipple head. So if your ERD is really accurate, you can round up at most 0.75mm, usually however there could be 0.5mm inaccuracy in ERD translating to 0.25mm inaccuracy for spokes. So rounding up even 0.5mm is probably not advisable. The screwdriver flats are 1.5mm so rounding down 1.5mm + 0.65mm = 2.15mm is perfectly fine, probably you could round down even more. – juhist Feb 6 at 9:15
  • The piece of the puzzle that gets left out of the conversation re: rounding up spoke lengths is that the threaded length on spokes and nipples is not universal. There are commercially available ones where you run out of threaded length with the spoke flush with the top of the nipple. Some Wheelsmith spokes are like that. The among of stretch also varies quite a bit with the gauge and tension. Rounding up is a recipe for getting burnt, there's just no reason to do it. – Nathan Knutson Feb 6 at 18:40

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