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Old 02-15-08, 05:43 AM   #1
lymbzero
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Wheel: ERD / spoke length / cross questions.

Hello,

I've got these rims but one of them is warped. ERD = 537
I'd like to replace the warped rim with a new one which has a larger diameter. ERD = 548

The original spoke length is 260mm
However with the new rim I calculated a 265mm spoke is needed. (DTCalc)

With the originally wheel I bought DT Comp spokes,
so I don't really want to dish out another $$$ for new spokes.

The question is ... Can I use the 260mm spokes on a rim that requires 265mm spokes?

My cheapskate mind thinks....
Tightened, the spokes pop out just above (1-2mm) the heads of the nipples.
If a nipple is 12mm then I have 7-8mm of nipple on the thread of the spoke.
Is that enough?

Thanks.

Oh yes.. and.. do people lace 2X on rear MTB wheels?
I've used 2X on fixed wheels and it seems to be fine.
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Old 02-15-08, 11:08 AM   #2
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1. 5mm short is a lot. You might be able to get away with it you might find yourself breaking nipples. I wouldn't do it. To me one of the prime reasons for building your own wheels is to see how good of a job I can do. Cheaping out on buying the right length spokes would be counter productive.

2. I've read more mumbo-jumbo on spoke crossings than just about anything. Ideally you'd like for the spokes to be tangential at the hub so they are pulling against more material and radial at the rim so that the nipples are straight. You can't have both.
If you accept the above criteria, with the majority of hub and rim combinations 28 spokes work best 2 cross, 32 and 36 work best 3 cross, and 40 works best 4 cross. Other possibilities might work but why would you want to?
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Old 02-15-08, 12:55 PM   #3
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One thing of note, nipples are generally not threaded all the way through, so your 7-8mm measurment might be a bit ambitious.

There is such a thing as longer nipples, though I don't know about how they are threaded internally nor do I know how much they cost.
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Old 02-15-08, 01:08 PM   #4
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A couple possibilities:

-See what happens to the required spoke length when you change the number of crossings with your hub
-Consider longer nipples
-Play around with different rim options/ERDs
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Old 02-15-08, 02:20 PM   #5
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I would seriously consider NOT reusing those spokes. If you reuse those spokes and they're too short (ie, only engage just a few threads on the nipple. You've basically defeated any sort of structural integrity by relying ONLY upon an, admittedly weak, brass or aluminum nipple. What you want is a spoke that is able to pass ALL the way through the rim and come up flush with the surface of the nipple (ie, passes beyond the driver flats cut into the surface of the nipple). That way the tension on the spoke is supported both by the nipple and a good portion of the spoke working together as one unit.
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Old 02-15-08, 03:13 PM   #6
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Go 2X if your original was 3X and that makes the spoke length work out, or even 1X if need be. The spoke calculator program should be able to tell you quickly.

The longer nipples I've used did not change the effective length of the spoke as they were not threaded any further along their length. They just allowed for easier use in more aero rim profiles. Maybe there are some different types out there, though.
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Old 02-15-08, 07:59 PM   #7
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Quote:
Originally Posted by Bob Barker View Post
Go 2X if your original was 3X and that makes the spoke length work out, or even 1X if need be. The spoke calculator program should be able to tell you quickly.
I had thought of using 2X on the wheel.

The original spoke is 260mm.

On the new rim:
3x would require 265mm (too short)
2x would require 255mm (too long?)

Now the question is 5mm extra too long?
eg1. Threads stick out 5mm over the nipple head.
eg2. Threads start entering into the second layer of the double wall rim.

Thanks again.

I will look into getting new nipples if the answer turns out to be kosher.
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Old 02-15-08, 08:23 PM   #8
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Quote:
Originally Posted by lymbzero View Post
Now the question is 5mm extra too long?
eg1. Threads stick out 5mm over the nipple head.
eg2. Threads start entering into the second layer of the double wall rim.
None of the above. With spokes that are 5mm too long you will run out of threads before you can tension the spokes.
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Old 02-15-08, 09:11 PM   #9
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Maybe you could go 2x and twist them
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