bowlofsalad

Hello,

I am a wheel building newbie, I've read a book and tons on the subject of wheel building but it seems that staggered spoke holes in the rim isn't an extremely common thing. https://i.imgur.com/NYTaXsj.jpg This is a picture of the rim. The spoke holes are 4.5-5mm to the left and right of the center of the rim to the center of the spoke hole.

It has been suggested that to calculate the spoke length I should remove the left and right (5mm each, 10mm total) spoke hole offset measurement from the flange spacing measurement. That doesn't take a ton off of the measurement, but enough (.6mm) to say instead of going with 184mm spoke length that I should go with 182mm or consider 183mm spoke length.

The parts I am using for this build are a mutant elektra rim (392mm ERD), a front shimano deore xt m756 (60mm hub flange diameter, 52mm flange spacing), and I plan to use sapim race (14/15/14) spokes with sapim polyax spokes in 3 cross lacing pattern. The spoke angle is kind of high, but that is why I am using sapim polyax nipples.

So if you were building this wheel, what spoke length would you use?

Is this how staggered rim spoke holes should be accounted for concerning the spoke length calculations?

Thanks!

FBinNY 

Rule No. 23 of bike repair. Disregard the inconsequential

The axial dimensions, ie. center to flange, or spoke offset in rim change spoke length by 1mm for every 10mm. So a 5mm change would only change the spoke length by 1/2mm, which is less than the rounding you'll do anyway. If a calculated length is between two available spoke lengths you might let these small fudge factor considerations guide you in which way to round.

However, you probably want some precise answer, so it's pretty straightforward. You used a CTF measurement in calculating, but the spokes aren't going to the center, so subtract the half zig/zag offfset form the CTF distances. On rims with all the holes offset to one side, add or subtract the offset accordingly.

But don't forget Rule No. 23

bowlofsalad

5mm each way, added together makes 10mm. Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting This picture might help you understand. Even if it were only .5mm difference in the calculated spoke length, if you were at (for example) 192.3 and then went to 191.8 due to staggered spoke holes on a rim, you'd then be rounding differently, .5mm makes a difference, it is consequential.

What is CTF?

ThermionicScott 

You'd be using 192mm spokes either way, right? Center-to-flange, as FBinNY spelled it out first.

FBinNY 

Thank you for taking the effort to ask a question then correcting the answer based on your newly acquired book expertise. I've only been doing this for 50 years and am still learning.

Let's take it one issue at a time.



CTF is center to flange (distance) I wrote it out the first time, and figured you'd pick it up, so I could abbreviate later on.

If your rims are staggered so the holes are 5mm apart, they're each only 2.5mm from the rim's center line. So, using your language 5mm divided by 2 = 2.5mm, which you'd subtract from the CTF. The rim in your photo has holes 4.5mm off the center line, so that's the number that counts (don't double it/ don't halve it).

And, yes, I knew some people would consider it consequential, which is why I gave you the calculation method.

So, .45 mm might make you round differently, but there are a number of fudge factors we never think about which is why I look at .45mm as a rounding bias rather than something to calculate.

Note, that there's latitude in spoke lengths and we often have to round to even lengths, so with your rims I'd consider it another factor telling me to round down rather than up, as I might otherwise do.

I tried to help, and hope this 2nd post clarifies. If you prefer to calculate precisely, feel free to do so, by netting the rim hole offset (from center, against the CTF.