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Old 03-09-14, 01:23 PM   #1
josephgallawos
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spoke length galldangit!

So, I used the pro wheel builder spoke calculator to determine the length of my spokes. Running alex advent. 700c on a Shimano deore xt fh-m756 a hub. The calculator lists a shimano deore xt m 765 but not a 756. it ALSO lists a shimano xt fh-m 756 (without the word deore) I figured surely this was my hub, since the numbers were exactly the same. it calculated a spoke length of 290 and 291 which I ordered. But in building my rim the final spoke insertion (three cross) was too damn long! By like 3 or 4 mm. Is that because I used the wrong hub in the calculator if so, why dont they list a shim. deore xt fh m 756? And should I just buy some damn calipers and calculate the spoke length myself?? I continue to be amazed by how confusing and un-uniform and un-systematic bike parts are. Clearly, they were not developed by mathematicians.
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Old 03-09-14, 01:31 PM   #2
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OK, start with eliminating the obvious. You have the hub, measure it and compare to the data you entered. If it doesn't match, you have your answer. OTOH if the hub data matches what you entered then there's another error.

Possibly the most common error, is calculating with (ie.) 4x, then building 3x. The other source of error is at the rim, so check the actual rim ERD and compare to the data you entered.

BTW- the old carpenters axiom - measure twice, cut once - applies to spoke length. If using specs to buy the components, and calculate spoke length, once you have the parts, you should measure for yourself and check the calculations before lacing.
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Old 03-09-14, 01:44 PM   #3
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If you continue to be amazed and are obviously distracted by that, why not just pay your lbs to build the wheel. You'd only be paying for the spokes once and the $25 - $30 in labor is likely cheaper than your time investment so far. Otherwise, just accept the reality of the vagaries of amateur wheel building and start over.

PS: Are you sure you got the two lengths in the correct hub flanges?
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Old 03-09-14, 01:55 PM   #4
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If you continue to be amazed and are obviously distracted by that, why not just pay your lbs to build the wheel. ....
The OP made a calculation error. he wasn't the first, and won't be the last, and even experienced, highly qualified mechanics make mistakes like this.

As for needing a caliper, you don't. All you need to measure hubs is a ruler, a piece of thin cardboard, and a pair of scissors.

Cut a wide slot into the cardboard so it it can clear the raised bearing area or freehub and lay flat against the flanges. Line up the edge with two opposite holes, and mark the centers. Remove the cardboard, and measure the width with a ruler. Voila, for a few cents you now have a hub caliper and can confirm flange diameter.
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Old 03-09-14, 01:58 PM   #5
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Are you sure you are crossing three spokes?
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Old 03-09-14, 03:03 PM   #6
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The OP made a calculation error. he wasn't the first, and won't be the last, and even experienced, highly qualified mechanics make mistakes like this.

As for needing a caliper, you don't. All you need to measure hubs is a ruler, a piece of thin cardboard, and a pair of scissors.

Cut a wide slot into the cardboard so it it can clear the raised bearing area or freehub and lay flat against the flanges. Line up the edge with two opposite holes, and mark the centers. Remove the cardboard, and measure the width with a ruler. Voila, for a few cents you now have a hub caliper and can confirm flange diameter.
Excellent technique. Thanks for the tip.
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Old 03-09-14, 03:41 PM   #7
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Did you enter the correct number of spokes in the calculator.
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Old 03-09-14, 03:50 PM   #8
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Did you enter the correct number of spokes in the calculator.
Obviously he didn't. otherwise he would have gotten the right answer. The challenge for him is to try to figure out where he went wrong. (see my earliest post for the likely suspects).

But since he started the post with uncertainty about the hub, he can start by measuring that. Then he can retry the calculation with confirmed info and see if he comes up with an answer 3-4mm shorter. If so, he may never know where he went wrong, but at least knows what's right.
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Old 03-09-14, 03:59 PM   #9
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@gruppo- Yea, money is not really the issue, and of course I could pay someone to do it, but then I wouldnt know how to do it myself. I am doing it for the learning experience, not to save money
@FB- thanks for tip. i will try that now. I did enter the correct number of spokes. I also crossed three spokes. Of course, I followed a utube tutorial to understand how to do it.
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Old 03-09-14, 04:17 PM   #10
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Update: Measured the flange. it is 60 mm, just as the spoke calc said it would be. checked my lace job against another 3 cross wheel and it is laced correct as best I can tell. Question. The holes in the alex rim do not appear to be offset and the tutorial said to use the shorter spokes on the disc side, which is what I did. Is that correct? Because the spoke calc says the left spoke is longer than the right and since the drivetrain is on the right, wouldnt that mean that the longer one is on the disc side? I am getting closer.....

aha!! now i am reading that the shorter spoke DOES go on the drive side. This is not what the tutorial said: they said the shorter spoke goes on the disc side. Gonna go and comment on the tutorial now. There are a million of them and I happened to pick a bad one I guess... My sanity is coming back. Thanks for helping a newbie... here is the video i used. http://www.youtube.com/watch?v=caCloMziaCk

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Old 03-09-14, 06:16 PM   #11
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Originally Posted by josephgallawos View Post
Update: Measured the flange. it is 60 mm, just as the spoke calc said it would be. checked my lace job against another 3 cross wheel and it is laced correct as best I can tell. Question. The holes in the alex rim do not appear to be offset and the tutorial said to use the shorter spokes on the disc side, which is what I did. Is that correct? Because the spoke calc says the left spoke is longer than the right and since the drivetrain is on the right, wouldnt that mean that the longer one is on the disc side? I am getting closer.....

aha!! now i am reading that the shorter spoke DOES go on the drive side. This is not what the tutorial said: they said the shorter spoke goes on the disc side. Gonna go and comment on the tutorial now. There are a million of them and I happened to pick a bad one I guess... My sanity is coming back. Thanks for helping a newbie... here is the video i used. http://www.youtube.com/watch?v=caCloMziaCk
Alex Adventurer 700c

D = 605mm (Flat of 12mm Standard Profile Nipple)


Shimano FH-M756

d = 61.0mm (Not 60.0mm)
c_left = 32.15mm SL = 292.95mm (32 Hole) or 289.25 (36 Hole)
c_right = 18.55mm SL = 291.76mm (32 Hole) or 288.06mm (36 Hole)

My guess is you calculated for 32 Hole and are trying to use spoke lengths for a 32 Hole wheel in a 36 Hole setup.

=8-)
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Old 03-09-14, 06:19 PM   #12
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...or you used an ERD of 607/608/609 combined with d = 60mm for the hub flange diameter.

=8-)
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Old 03-09-14, 06:30 PM   #13
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Well, maybe pro wheel builder is wrong? here is what they give me. Note that I did use the correct hole number of 36.
Pro Wheel Builder Spoke Length Calculator


Left spoke length: 291.3
Right spoke length: 290.4

But if the shorter spoke goes in the drive side that is obviously my problem no? as i mentioned before, the tutorial i used said to do the oppposite

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Old 03-09-14, 06:35 PM   #14
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Shorter spoke goes drive side...

=8-)
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Old 03-09-14, 06:50 PM   #15
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....aha!! now i am reading that the shorter spoke DOES go on the drive side. This is not what the tutorial said: they said the shorter spoke goes on the disc side. Gonna go and comment on the tutorial now.....
Regulars here on BF have heard me rant about what I call GPS knowledge, or paint by numbers wrenching namy times. here's a perfect example of why I hate it so much.

Regardless, of what the tutorial might have said, had you given it some thought, and looked at the big picture, you'd have figured out that the shorter spokes go to the flange closer to the center (lower CTF). It doesn't matter which is which, it's the distance that matters,

OTOH, I strongly doubt that this error accounted for your problem by itself. Typically CTF distances account for about 1mm spoke length change for every 10mm of CTF. In a normal rear wheel, that would be 2mm difference between the right and left spokes. On a rear disc wheel, the difference would be less since the left flange is also closer to center.

Since the right/left error is worth 2mm at most, and you're off by 3-4mm I suspect there's more going on. Probably as MrRabbit pointed out, an error in measuring the rim's ERD.

My advice: STOP, THINK, and CHECK EVERYTHING before buying more spokes and relacing.
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Old 03-09-14, 07:06 PM   #16
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sound advice. thanks. I guess i will cross check several spoke calculators before re=lacing it with the exhisting to see if it does account for the error or not. I have a feeling by the time i am done with this wheel I will at least know the pattern by heart
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Old 03-09-14, 07:27 PM   #17
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Quote:
Originally Posted by mrrabbit View Post
Alex Adventurer 700c

D = 605mm (Flat of 12mm Standard Profile Nipple)


Shimano FH-M756

d = 61.0mm (Not 60.0mm)
c_left = 32.15mm SL = 292.95mm (32 Hole) or 289.25 (36 Hole)
c_right = 18.55mm SL = 291.76mm (32 Hole) or 288.06mm (36 Hole)

My guess is you calculated for 32 Hole and are trying to use spoke lengths for a 32 Hole wheel in a 36 Hole setup.

=8-)
wondering where you are getting 605 for rim D. The specs are saying 608. If I use 608 my spoke lengths are (almost) correct and maybe i was exagerating how much too long they were. Here is what the bike institute gives me. DS-289.5 Non ds 290.6. The spokes I ordered are 290 and 291. Gonna re-lace. nothing to lose at this point but time.
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Old 03-09-14, 11:30 PM   #18
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You'll see 603.5, 605, 605.5, 606, 607, and 608 all over the Internet.

Partly because there is variation from production run to production run.

But more importantly, because everyone has a different aiming point in the nipple used.

I aim for the bottom of the screwdriver slot in a standard profile 12mm nipple to allow 1.5mm of threading overhead to ensure I reach the desired tension WITHOUT running out of threads.

Some folks aim for the top of old 10mm standard profile nipples.

If they publish a number without a reference - you simply cannot trust the number.

Best thing to do is to measure your own ERDs. That's keep you out of trouble.

The bigger question you need to ask yourself is: "Do I understand what ERD is?"

=8-)
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Disclaimer:

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2. I like anyone will comment in other areas.
3. I do not own the preexisting concepts of DISH and ERD.
4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
5. My all time favorite book is:

Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life
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Old 03-11-14, 09:39 AM   #19
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Did you confuse directions for building the disk front wheel with the disk rear? I think both will end up with some dish albeit on different sides of the hub.
I concur that it is good (and fun) to try these things on your own if so inclined. Not a bad idea to take the finished product to your LBS to check for proper tension and such.
And remember... that's why they put erasers on the other end of pencils.

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