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Old 09-11-05, 06:05 PM   #1
GetOutOfNJ
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Is exact spoke length important?

I built my first wheel, a mavic ma3 rim with an IRO flip/flop hub, 36 spoke, using 293 spokes, 2mm longer than I figured I needed, and it seemed to work out. I'm going to build up the front one now... is there really any functional difference between 291 and 293?
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Old 09-11-05, 06:51 PM   #2
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Quote:
Originally Posted by GetOutOfNJ
I built my first wheel, a mavic ma3 rim with an IRO flip/flop hub, 36 spoke, using 293 spokes, 2mm longer than I figured I needed, and it seemed to work out. I'm going to build up the front one now... is there really any functional difference between 291 and 293?
No functional difference other than some (really) minute amount of weight. As long as you can get your spokes tensioned properly and they don't protrude past the nipple ends you should be fine. If they are protruding, that is not good and you will likely get flats. Also, I'm assuming you realize that the front wheel is not necessarily going to use the same length spokes as the rear.
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Old 09-11-05, 07:06 PM   #3
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The ideal length has the spoke end just at the bottom of the nipple. Real world, this almost never happens. If the spokes stick way out you might have a problem with tem touching the tube through the rimstrip, in a boxed rim this is unlikely. The only real issue is thread engagement. You get the best engagement with the spoke ending at the botom of the nipple, anything else gives you less than the best thread interface(Not entirely true as some spokes have a lot of threading on them.)
I like to keep it with in 1mm of the correct length(some spokes only come in even #)
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Old 09-11-05, 08:13 PM   #4
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Its good to get the spokes right, because its a pain in the ass to unlace the wheel and relace it with different spokes when you have the wrong size. I've been there--no fun
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Old 09-12-05, 04:25 AM   #5
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Originally Posted by Rev.Chuck
The only real issue is thread engagement.
Oh good. Yesterday I got to disagree with Sheldon Brown today it's Rev. Chuck. Sydney's next.

Actually, I've encountered a couple of issues, other than thread engagement, with wrong size spokes. One that has already been mentioned is spokes protruding past the nipple. If you are using single wall rims, that's the sure road to flat tire city. The other is running out of threads for tensioning the wheel. That's the route to broken spoke city. Neither is a place you want to go.

Unfortunately, I'm not smart enough to predict if you'll run into either problem until after you lace the wheel. Like the Rev., my rule of thumb is plus or minus 1mm. If I didn't have easy access to the correct size I'd definitely take a chance with spokes that were only 2mm too long but I don't think that I'd extend that to 3mm too long except in an emergency.
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Old 09-12-05, 03:33 PM   #6
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Retro, do you want to disagree with me to?
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Old 09-12-05, 07:03 PM   #7
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I'd rather have them 1mm or even 2mm short. As Retro pointed out, the worst that can happen is to run out of threads before reaching ideal tension. This is a fairly common problem on the drive side rear spokes. I'll always buy them short.

Al
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Old 09-13-05, 12:06 AM   #8
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Hi!

I'm contemplating doing my first wheel rebuilds with Mavic MA3s. I have the rims but hav'nt purchased the spokes yet. I've downloaded what is reputed to be a pretty good spoke length calculator. My vintage hubs are not listed in the downloaded files so I have to measure the hub spoke hole diameters with a vernier caliper. I enter that information plus the dishing dimensions for my rear wheel and the program computes the spoke length. It has gotten good reviews.

If the spokes extend beyond the nipple a mm or two too long after tensioning, why can't one grind the excess length down with a Dremyl or Die grinder? With the eyeletted double walled MA3s, isn't the slight spoke extension a non-issue?

I'm a newbie so please excuse the ignorance.

Sinchi
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Old 09-13-05, 01:19 AM   #9
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Yeah, the double-walled MA3 should be fine with a couple mm of spoke poking through. You'd need about 5mm sticking through in order to get above the level of the rim-strip. However, too short of a spoke and you bottom out the nipple on the threads and can't tighten them past a certain point. Forcing it past this point rounds off the threads on the nipples and will reduce the numbers of threads for gripping...

When using those spoke-calc programs, I just subtract 1mm for the rear drive-side and add 1mm for the non-drive side.
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Old 09-13-05, 11:57 AM   #10
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Originally Posted by DannoXYZ
When using those spoke-calc programs, I just subtract 1mm for the rear drive-side and add 1mm for the non-drive side.
Then whats the point of using a calculator?

one thing everyone is missing is the assumption all spokes and nipples are threaded the same length. They are not.

Whats proper thread engagement? I dont know. But, somewhere along the line I read something about three times the diameter of the bolt. So, in other words, if you have 2 mm spokes you should have 6mm of thread engagemt.

Short.....as long as your engaged at least 3 times the spoke diameter it doesnt matter

Long....as long as they dont protrude past the nips on single wall rims and leave adequete thread for truing your ok. BTW there are tools for cutting excess spoke length.
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Old 09-13-05, 06:10 PM   #11
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Quote:
Originally Posted by DannoXYZ
However, too short of a spoke and you bottom out the nipple on the threads and can't tighten them past a certain point. .


Forgive me but that is not correct. It's when the spokes are too long that the nipples bottom out (run out of threads). Better to be 1mm short than 1mm long.

I recommend buying the drive side rear spokes 1 or 2 mm short of the calculated length, every time. Spokes stretch under high tension.

Al
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Old 09-13-05, 06:15 PM   #12
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Quote:
Originally Posted by Al1943
Forgive me but that is not correct. It's when the spokes are too long that the nipples bottom out (run out of threads). Better to be 1mm short than 1mm long.

I recommend buying the drive side rear spokes 1 or 2 mm short of the calculated length, every time. Spokes stretch under high tension.

Al
Sorry brain fart... yeah I meant too long..
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