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Double check my front wheel spoke calculations?

Old 03-06-20, 05:32 AM
  #1  
bikerbobbbb
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Double check my front wheel spoke calculations?

Anyone want to give me a second opinion so I order the correct spoke lengths?

https://www.prowheelbuilder.com/spokelengthcalculator/
My exact front hub isn't on here, but I'm using...
Front
Mavic
A719 I don't have the rim yet, but this is what I'll get. ERD is on the specs for this.
Shimano


Deore XT M760 hub front I actually have a Deore LX front hub HB-T780.
36 spokes
3 cross <-- 3 cross is the standard spoke lacing, right?


That gives me left and right spoke lengths of 292.1mm.

I do have the hub purchased now. And I've got my caliper. I'll measure this actual hub myself. When measuring a hub for spoke length, do you set the caliper pointers in the very middle of the holes?



https://shop.mavic.com/en-us/a-719-j...3283&1035=3501
Mavic says the ERD is 598mm under the specs section on here.

So if I change that ERD on the calculator to 598 I get this....



I'll have to measure the actual hub.

I'm also wondering -- Is it better to error on a little longer or a little shorter for spoke length?
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Old 03-06-20, 05:39 AM
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Yeah, it's three cross. And I checked on my bike. That one cross is pretty much right on the hub though, but it's three.
cross 3 stronger than standard 2 lacing? / thinking on redoing spokes
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Old 03-06-20, 05:54 AM
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How would you even get a real ERD on a rim if it's just the rim and not perfect round yet? I read someone on here was taking several measurements and using the average.
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Old 03-06-20, 05:59 AM
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And here's some pics. On a few I tired measuring on the ends which I don't think is correct. It looks like measuring in the of the middle of the hub ends or middle of the holes is correct.

I'm also not 100% sure on the 16mm since I can't quite line it up with the calipers. I guess it's 16mm.







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Old 03-06-20, 06:03 AM
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One of my previous posts on the 2016 rear wheel builds had the same question with an answer I think about whether it's safer to go shorter vs. longer on spoke length. I don't know if I'm going to dig for that.

Longer means they'll stick out more on the rim tape side possibly. And the threads will run out when it's tightened.
Shorter means less inside the rim.... possibly more threads then unless the spoke doesn't even go inside the rim, as in the nipple is the only thing connecting there because the spoke doesn't even get to the rim.... That would give more threads though. I'm leaning toward going shorter.

For longer, I was wondering if you could file the end off a bit if it's too long, if that's even possible. Then again, that's probably a lot of work. Then you get rid of some of the 10mm of threading, and unless you've got the $500 thread tool, you're out of luck. It's better to just buy new spokes a little shorter at that point.
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Old 03-06-20, 06:09 AM
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So if my measurements confirm the other hub I used on the spoke calculator, that gives me either 292 or 290mm. I guess I'd go with 290mm then.

If it matters, on my current rear wheels I've wondered if I'm tightened down to the ends of the threads sometimes, like where the bottom of the thread (toward the hub) is taking in some of the spoke without thread.

Then again, for shorter spokes, if they're not going into the nipple that far, it's probably not as strong. Having the spoke go through the nipple and little out would probably be as strong as it gets.


1 36 spoke rim, front so same length on each side means 36 spokes needed (maybe I'll get 45 for some spares), 36 nipples (12mm I think) are needed.
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Old 03-06-20, 08:02 PM
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bikerbobbbb,
I think, since you have posted a cross section of the rim picture you have plenty of room left. So the spoke length is not as problematic as if they were to stick out a bit from the end of the nipple, the spoke will not puncture the tube. And more purchase for the threads is better for a stronger wheel. The potential down side is that you will need to do a finish with a spoke wrench instead of a screwdriver. JMHO, MH
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Old 03-07-20, 10:15 AM
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Damon Rinard's Excel Spreadsheet, which includes a database of rims and hubs.
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Old 03-08-20, 05:16 AM
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Thanks for the replies.

Are there any other spoke calculator websites?
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Old 04-11-20, 09:55 AM
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I found some other calculators. After those, the excel sheet was easier. I'm getting 290.6-8 roughly. Would round up to 291mm, but I don't think I can get that. And it's just a mm.... So is 290 or 292mm better? If it matters... It's a double wall rim. It probably doesn't matter if it sticks out a little on the rim side. So that leaves the 10mm of thread on the end of the spoke. ...How much thread does a nipple have on the inside? The entire nipple length or just the squared end?

If it's shorter... There's more thread on the spoke? If longer, less thread.... Which makes it sound like 290mm might be the way to go.
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Old 04-13-20, 09:37 AM
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So from this post,
https://www.kstoerz.com/freespoke/te...engagement.php

And glancing at this post,
Nipples (The kind on a spoke)

It looks like slightly longer is better, and threads are in the screw head side of the nipple. In that case, I'd go with 292mm spokes over 290mm.
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Old 04-13-20, 11:30 AM
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Originally Posted by bikerbobbbb View Post
So from this post,
https://www.kstoerz.com/freespoke/te...engagement.php

And glancing at this post,
Nipples (The kind on a spoke)

It looks like slightly longer is better, and threads are in the screw head side of the nipple. In that case, I'd go with 292mm spokes over 290mm.
291mm is the length spoke that you need. Any spoke manufacturer can make 291mm spokes for you. Spoke calculators take into consideration the length of thread on the spoke. I wouldn't gamble with any other length spoke.
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Old 04-13-20, 12:30 PM
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The Park tool website has a pretty good description of how to accurately measure rim ERD.

If you accurately enter the information into a length calculating spreadsheet like spocalc you will probably get the length calculated with no allowance for spoke stretch or rim diameter contraction. If you want to know exactly what's going on with these calculators, you can find an online html copy of the Brandt "Bicycle Wheel" book and read the part about how length is calculated and the geometry involved. spocalc, for one, appears to use the exact equations as used in the Brandt book as when you compare the spocalc figure with the Brandt calculation,you get the same lengths.

So, what this means is that because spoke stretch and rim contraction are neglected, the calculated spoke length will probably be 0.5 mm to 1.0 mm longer than actual length in practice. "Probably", because there may be some calculators that take stretch into account.

What this means to you is that if you have a calculated spoke length aimed at the bottom of the screwdriver slot(state 3 @ https://www.kstoerz.com/freespoke/te...engagement.php) you can go 1 mm or so either way and still have good spoke engagement. So, in your case, spoke length of 290 - 292 will, if your entries in the calculator are good, give you good results. Either 290 or 291 will probably result in a spoke end that's at or slightly beyond the bottom of the screwdriver slot with little chance of running out of spoke thread. Happy wheels will result. In my experience, spokes always build a bit longer than nominal values.

On measurements: reference values for ERD and hub dimensions that you find on the internet may or may not match the ideal numbers that you want to use in your calculations. For example, ERD measurements published by Mavic are reputed to be aimed at the inner diameter of the actual rim rather than the diameter of the imaginary circle of the spoke screwdriver slot bottoms of the nipples. So, supposedly, Mavic published ERD values are alleged to be about 3 mm less than ideal which would result in spoke lengths about 1.5 mm shorter. Also, ERD values for the same rim model are not guaranteed to be a constant through all space and time. Velocity, supposedly, changed some rims resulting in actual measured ERD values that vary a bit. These facts about rim manufacturing and published ERD values -- these are the reasons that people say you should accurately measure the actual rims that you will be building with. Then there is the fact not all rims are actually round when you get them. In my limited experience, Mavic and Velocity rims are pretty round, Sun rims, not so much. So, you make two or three measurements around the rim and see if they are the same and then estimate what they will be if the wheel were round. Hub dimensions too. At least make some decent measurements to make sure the hub you are using and the published values make sense with respect to each other.
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Old 04-13-20, 03:40 PM
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Thanks. Still studying out your post. I suppose I should order the rim then, and check those measurements myself. I figured the manufacturer must know and be precise if they're precise enough in the wheel creation. It won't hurt to go slowly, and I can hone in better on how to measure ERD.

I double checked where I got my last spokes from. They do have 291mm. I was thinking they only had even numbers for some reason. 291mm is probably the way to go then.
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Old 04-27-20, 09:03 AM
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This page gives an ERD of 602mm.
Mavic A719 700c, 29er rim dimensions | Freespoke

Mavic is 598mm.
https://shop.mavic.com/en-us/a-719-j...3501&1039=3515


It does look a lot easier to measure ERD just using two spokes. As long as the spoke end is lined up with the screw drive slot in the nipple, it's just measuring spoke length and using a caliper, nothing to mess with for a loose tape measure or where on the nipple head to measure from exactly.
https://www.parktool.com/blog/calvin...e-rim-diameter
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Old 04-27-20, 09:16 AM
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So two spokes, each 292mm. That's 584. So my spokes shouldn't overlap and the caliper should work.

I'm thinking maybe measure all of them. That's 18 ERD checks. The nipples are going to move though... unless I put paper or something in to hold them. Tape doesn't sound like a great idea.





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Old 04-27-20, 09:27 AM
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This website says ERD 600.5
https://www.cyclecycle.info/weight-w...desc&order=ERD
Some spokes come just a bit short or longer depending on the manufacture.
The rear drive side generally should be 2 mm shorter spoke than the non-drive side.
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Old 04-28-20, 08:23 AM
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Measured the ERD. I measured all the 2-spokes around, so 18 times.


So I get 602mm for the ERD, unless I did something wrong, but that's the calipers in the j-shaped ends with the spoke out to the end of the nipple where the screw driver slot starts.
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Old 04-28-20, 08:55 AM
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Build the wheel!
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Old 04-28-20, 09:19 AM
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Here's with the highest and lowest measurements taken out. I'm still wondering why the very last ERD spoke set check was higher like that. It was on the opposite side of the stem hole if that matters. On the other side of the rim, across from the stem hole, that's where the weld is for sure.

When I took a metric tape measure and eyeballed it, I got 593-596mm +2mm +2mm for the inner rim to screwdriver slot on the nipple head, giving me about 595-598mm ERD.




Another trick I found for popping the nipples off 18 times was to mark the spoke with a sharpie so I was putting it back at just about the same place each time.
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Old 04-28-20, 09:23 AM
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I'm leaning toward 292mm now.
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Old 04-28-20, 09:41 AM
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The Sheldon Brown excel calculation. I'm getting just over 292.5 twice now. If I make the ERD 601 though, then this excel is 292.2mm. I was wondering if I measured ERD wrong maybe. I found a site saying 600.5mm. Or that was on this excel sheet I think.

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Old 04-28-20, 09:50 AM
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Yuck. I got 294 on one site. 291 on another. They're using different ERDs though compared to my wheel or even the preprogrammed hub on one site I found had slightly different numbers.

https://www.sapim.be/spoke-calculator
gave me 294

https://leonard.io/edd/
gave me 291.3
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Old 04-28-20, 10:06 AM
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Just build the frickin wheel.
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Old 01-23-22, 09:01 AM
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I guess I'll go with the 292mm. Double butted again. I don't want to remeasure ERD again like I did... almost two years ago.

I've had the rim and hub sitting around this whole time. On my 2016 rear wheel builds, the black Shimano FH-T780 hub cracked when I was truing it up recently. Oops. Too tight. It actually cracked and a piece is split off. The T780 I can't find anywhere anymore, so I'm out of luck just buying a new one and swapping it in ("just" swapping in a hub). I find another one that should work, I hope, but I want to get free shipping, so if I order these spokes, I should get free shipping.

Next steps...
Order the new rear hub and these front wheel spokes.
Take measurements on the new rear hub. Calculate the correct spoke length. I'm hoping the used spokes will work. I'm going to stick used spokes on anyway. I've got this would-have-been front wheel rim which is the same as my rear wheel rims, so I'm going to carefully take off each spoke on the broken-hub rear wheel and transfer them to the would-have-been-front-rim and the new rear hub. If the spokes are in the exact place, I'm thinking some wear will be the same. I'm hoping the new rear hub is close enough for specs that the used spokes still work. If not, then I'll just order new spokes for the rear wheel.
So the would-have-been front rim will become the rebuilt rear wheel with new rear hub.
And then second front wheel will be the used rear wheel rim, new spokes, and the new two year old new hub I've got already. The front wheel doesn't get nearly as much weight, so I don't think a rim that probably has about two years of use on it will be a big deal.

For the front wheel build though, that is a different rim, but it's the exact same model. The rim still has the broken rear hub and spokes on it right now.
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