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Spokes too Short! But calculations seemingly correct???

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Spokes too Short! But calculations seemingly correct???

Old 03-13-14, 08:01 PM
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nybiker
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Spokes too Short! But calculations seemingly correct???

Hi All,

Hoping a pro wheel builder can give this novice some advice

I'm building my second set of wheels ever. First set came out perfect. NOS Campy Chorus hubs on Mavic A719 rims for my tourer.

This time, I'm building wheels for my commuter and decided to take advantage of the disc brake mounts on my frame.
So I purchased a new set of Shimano Deore XT centerlock hubs and some Velocity Dyad 700c rims (Australian made).

I measured the hubs and ERD and entered the info into Spocalc. 32 Spokes / 3 cross
Front Hub Shimano HB-M785

Measurements for the front wheel are:
N, total number of spokes 32
ERD, effective rim diameter 596.0
OSB, offset spoke bed 0.0
WL, width from center to left flange 22.7
WR, width from center to right flange 34.2
dL, left flange diameter 44.2
dR, right flange diameter 41.2
S, spoke hole diameter 2.6
X, cross number (decimal allowed)(optional) 3.00
WL_effective = W + OSB 22.7
WR_effective = W - OSB 34.2


And the calc spit out: 289.8 for the Left and 291.4 for the right

SO, I got 290 Spokes for the left, and 291 for the right

However, after installing the first 2 sets of spokes, the third set seem to be too short to thread into the nipples.

WHAT HAVE I DONE WRONG? :'-(
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Old 03-13-14, 08:07 PM
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Are you sure you're not building it 4-cross?
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Old 03-13-14, 08:10 PM
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The two most common errors when calculating spokes are,

Wrong ERD, either bad spec data, or measuring yourself and forgetting to add for the nipple heads.
Cross mismatch, calculate for 3x build 2x or a comparable error.

Another error arises from getting the wrong spokes delivered and not checking.

After those two, anything is possible. Recheck all measurements and the math to see where you might have gone wrong.

Also recheck that you're counting crosses correctly. Sometimes people err, trying to cross one more spoke than intended because they didn't count the cross right at the flange.
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Old 03-13-14, 08:11 PM
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Yeah, I wish that had been my problem easy fix.
I didn't mention that after I tried once, I disassembled and tried again only to find the same problem.
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Old 03-13-14, 08:14 PM
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Thanks,

The spokes were the ones ordered and I have re-measured since, but I'll give that another go.

Adding for the nipple heads...is something I did not do. I don't recall reading about that in the books I consulted, however, that could be the problem.

QUOTE=FBinNY;16575955]The two most common errors when calculating spokes are,

Wrong ERD, either bad spec data, or measuring yourself and forgetting to add for the nipple heads.
Cross mismatch, calculate for 3x build 2x or a comparable error.

Another error arises from getting the wrong spokes delivered and not checking.

After those two, anything is possible. Recheck all measurements and the math to see where you might have gone wrong.

Also recheck that you're counting crosses correctly. Sometimes people err, trying to cross one more spoke than intended because they didn't count the cross right at the flange.[/QUOTE]
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Old 03-13-14, 08:27 PM
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Originally Posted by nybiker View Post
Thanks,

The spokes were the ones ordered and I have re-measured since, but I'll give that another go.

Adding for the nipple heads...is something I did not do. I don't recall reading about that in the books I consulted, however, that could be the problem.
This is a common source of error. ERD is the misnamed effective RIM diameter. In fact ERD is the diameter of the imaginary circle formed by the ends of the spokes. Essentially it's the diameter at the spoke holes, plus the height of the spokes above that -- into the spoke head.

Since ERD is the desired height of the spokes, spoke calculators will produce a spoke height equal to the ERD entered.

If you measure your own rims, either add 6-7mm for two nipple heads, or add 3mm or so to the calculated spoke length. Either method is fine (I use the second) but be consistent in how you measure and calculate.
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Old 03-13-14, 08:43 PM
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I just re-measured the rim and the ERD of 596mm looks right - The diameter just to the spoke holes is about 587mm. The mystery continues...

Originally Posted by FBinNY View Post
This is a common source of error. ERD is the misnamed effective RIM diameter. In fact ERD is the diameter of the imaginary circle formed by the ends of the spokes. Essentially it's the diameter at the spoke holes, plus the height of the spokes above that -- into the spoke head.

Since ERD is the desired height of the spokes, spoke calculators will produce a spoke height equal to the ERD entered.

If you measure your own rims, either add 6-7mm for two nipple heads, or add 3mm or so to the calculated spoke length. Either method is fine (I use the second) but be consistent in how you measure and calculate.

Last edited by nybiker; 03-13-14 at 08:44 PM. Reason: TO include quote from FBinNY
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Old 03-13-14, 08:43 PM
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Make sure you have the pattern right side-for side.
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Old 03-13-14, 10:50 PM
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Originally Posted by Retro Grouch View Post
Make sure you have the pattern right side-for side.
Ditto- whenever I've come up with spokes "too short", it's been because I'm one hole off. It's easy to do.
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Old 03-14-14, 12:12 AM
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i can't tell you how many times i've had to re-lace a wheel because i laced it wrong. it surprises me how many different ways i can screw it up if i'm not paying attention . sometimes it shows the symptoms you've described, i've rarely bought spokes of the wrong length due to miscalculation, but i'm sure it's possible though.

if i use spoke length software off the internet, and i do, i usually get a "second opinion" from a second internet site. and see how they compare.
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Old 03-14-14, 02:37 AM
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I ran your numbers with EDD spoke calc and got 290 and 292. That 1 extra mm shouldn't make any appreciable difference, the rim should lace up just fine either wit 290/291 or 290/292 spoke sets.

I am wondering if you were off a hole when you went to the other side of the hub?
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Old 03-14-14, 06:15 AM
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Originally Posted by bobotech View Post
I ran your numbers with EDD spoke calc and got 290 and 292. That 1 extra mm shouldn't make any appreciable difference, the rim should lace up just fine either wit 290/291 or 290/292 spoke sets.

I am wondering if you were off a hole when you went to the other side of the hub?
This is what I would guess too. Assuming you're starting on the NDS, when you flip it over you should start one hole to the right of the first spoke. If this is off, what you're describing will happen.
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Old 03-14-14, 06:48 AM
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Thanks everyone. I'll be giving it another go this weekend and hopefully whatever I was doing wrong will be righted. I'll let you know.
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Old 03-14-14, 07:50 AM
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This is pretty obvious and I'm almost certain it's not your problem, but if you thread the nips too far onto the spokes when installing the spokes it makes it progressively harder to get the subsequent nips started. It depends on the pattern as in some cases the spokes are quite bowed before tensioning and are effectively shorter until tensioned.
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Old 03-14-14, 08:18 AM
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Originally Posted by Looigi View Post
This is pretty obvious and I'm almost certain it's not your problem, but if you thread the nips too far onto the spokes when installing the spokes it makes it progressively harder to get the subsequent nips started. It depends on the pattern as in some cases the spokes are quite bowed before tensioning and are effectively shorter until tensioned.
^^^^ This. It is very common to thread the spoke too deep into the nipple during the initial lacing and make it harder to finish up the last of the spokes. Especially on a rear it is common to have a whole side improperly dished during the initial lacing and make it really hard for the other side spokes to reach. This happens a lot with one side radial. But with both sides crossed, if you did all the spokes on both sides pointing one direction first (as is normal), and threaded them too deep into the nipples, when you twist the hub to start the spoke going in the other direction, the hub won't rotate far enough. Just try loosening all your nipples as far as possible without unthreading them completely. If that helps, then the only thing to watch out for is that your spoke end nearly do reach the nipple tops when the wheel is fully tensioned and trued. If that is the case, the spoke lengths were right. You don't want the spokes to end below the nipple shoulders.
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Old 03-16-14, 12:35 PM
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Well, I've overcome whatever it was that I was doing wrong. It wasn't that I threaded the spokes too much. I was careful to only do about 3 turns on each. I think it had to do with putting the spokes in the wrong holes. Anyway, I really appreciate everyone's help!
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Old 03-16-14, 12:44 PM
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Good job, and remember, no good can come from putting things in the wrong hole.
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