bowlofsalad

Hello,

I have very little wheel building experience and I am working on fully assembling a wheel for the first time. I was about ready to purchase some spokes when I realized that the spoke holes on the rim are towards the edges of the left and right of the rim, not down the center. Typically, rim offset seems to be a reference to the spoke holes all being on one side of the rim. Are there any special considerations to be made when calculating spoke length and assembling wheels with this type of rim?

I've measured the ERD with both nipples each within paralleled sides and both sides came up with the same length. After considering this for a while I am guessing that I might not need to worry about this but I'd rather ask and hear what others have to say instead of discovering that I wasted the cash on bad spoke lengths.

Thanks!

JohnDThompson 

In my experience, the offset doesn't result in a significant change in spoke length.

J.C. Koto

I'm no expert either but I'd do this:

1. Measure the offset from the rim's center-line.

2. Add (or subtract for that matter) that value to the hub's center-to-flange distance for both sides.

3. Recalculate spoke length.

You'll probably notice it's a minute enough difference to allow the same spoke length either way. I just did this calculation for a couple different hypothetical wheels and it resulted in the same spokes.

bowlofsalad

Thanks for the reply. I am using a digital caliper, placing one edge in the center of the inside of the rim (measuring on the inside of the rim, not the outside), and placing the other edge of the caliper close to the center of the hole. The comes to around 5mm from each side, following your idea I go from 183.4 to 182.7. That seems fairly substantial. I was likely to go with 184mm spokes but with that measurement, I'd probably go with 182.

Am I measuring the offset correctly? I was thinking that maybe I should measure to the edge of the spoke hole instead, but I am uncertain.

I've been doing plenty of reading on the subject, skimming and re-reading sections of a wheel building book I read, and I think the term I am looking for is staggered spoke holes. Your technique seems to have been suggested on this matter, but how it's done is vague.

J.C. Koto

Lets back up a second, I just reread your OP: Were you able to get the manufacturer ERD spec.? Also, how did you measure the ERD again? I'm pretty sure the exact opposite spoke holes on a staggered-spoke rim are on opposite sides of the rim's center-line.

This is what's confusing me.

Also, you might be able to get better luck if you post what components and which lacing pattern you are using.

J.C. Koto

Also, all advice I've seen is to round spoke length down rather than up so you don't bottom out the spoke threads with the nipple thus precluding the ability to tighten the wheel to the correct tension so, either way, 184mm spokes would be too long.

bowlofsalad

The rim is a mutant elektra (406mm) Robot Check Here is an example of it. You can see the spoke holes are staggered, one on the left, then one on the right, alternating. What exactly I meant for measuring the ERD was I placed the nipple on the top and bottom of the rim, both on the right, and then both on the left. I hope this makes sense. I've read a lot on the subject of wheel building, it's often recommended to never take what anyone claims is the ERD and to measure it yourself.

I am not sure I understand what you meant by "I'm pretty sure the exact opposite spoke holes on a staggered-spoke rim are on opposite sides of the rim's center-line." https://imgur.com/NYTaXsj This picture might help illustrate and answer some things.

The precise technique I used is I cut down two spokes to 100mm and placed a thin rubber band with some electrical tape on the end of each spoke. Then I put a nipple on each spoke while on the rim and measured the space between each spoke. The distance between each spoke for this rim is 192mm, I then added 200mm to that to give me an ERD of 392.

The hub is a front shimano deore xt m756. It seems pretty nice compared to the other hubs I've used in the past but I regret getting it a little as it's pretty big.

I plan to use sapim polyax spokes with sapim race (14/15/14) spokes, cross 3 lacing. The measurements I have are ERD: 392mm, hub flange diameter is 60mm and the inner flange spacing is 52mm (26mm each way from the center). I doubt it matters, but I measured the spoke holes on the hub to be 2.5mm or so. I probably wouldn't use 3 cross lacing for this wheel if I wasn't pretty set on using double butted spokes, I haven't been able to find double butted spokes below 180mm (or an odd length for that matter), and 3 cross gives me the spoke length I'd need.

As for the spoke length, I've read similar advice, but I have also read that it's fine to round to 1mm in either direction. Meaning if you come up with 236.5mm for spoke length, going with 236mm or 237mm for spoke length is perfectly fine. However, when coming up with 182.8 with your suggestion instead of 183.3, I get into sort of a tight spot. Either I go with 184mm or 182mm, that seems like kind of a big deal and right now it feels like a little bit of a gamble due to uncertainty of technique.

So I am unsure if I absolutely should remove anything from the flange spacing measurement, and if it is unquestionable that this is the thing to do for stagger rim holes, I am not sure if I should go with 6mm or 10mm (depending on how I measure).

J.C. Koto

Yeah sorry, I was wrong about that anyway. Off-by-one error on my part. You can safely disregard that comment.

J.C. Koto

Assuming your ERD measurement is correct I wouldn't worry about any offset and just go with 392 without fudging other measurements.

Unless you're absolutely married to the idea of the sapim race (14/15/14) you might consider getting 183mm double-butted spokes in some other brand (since the sapim race spokes don't seem to come in 183mm). That would solve the issue.

bowlofsalad

I am ok with using another brand. From what I can tell so far, I've only been able to find DT swiss competition at 183mm coming in at a radically higher price per spoke (while also needing to buy a much larger volume of that spoke length).

If 5mm (10mm total) is what I am taking off the flange width measurement, 182.6mm is the spoke length, 183mm might be closer but I'd feel perfectly fine with 182mm in that case.

fietsbob

the spoke holes in the rim are over the centerline beween the axle locknut ends .
Dish is to make room for all the 'speeds' on the cassette..


if they are offset in the rim then the dish stick comes out, so the rim centerline is the priority
and the spoke tension gets to be a T***** less different

between the DS and NDS (thats the design plan at least..)

bowlofsalad

This is for a front wheel. The concern is accurately calculating spoke length with staggered spoke holes in the rim.

bowlofsalad

It's a bummer I can't change the thread title to something more like, "How to calculate spoke length with staggered rim holes?"

J.C. Koto

You could create a new thread with that title, perhaps in the bicycle mechanics subforum.

FBinNY 

+1

While rim offset can be thought of as reducing, or changing the CTF distance, and purists may want to calculate it, there's no reason to bother.

CTF and rim offset affect spoke length by roughly 1mm for every 10mm, ie. hubs with CTFs of 38/20 use spoke lengths 2mm apart. So adjusting these by the typical small amounts of rim offset is meaningless in the scheme of things where you're rounding to full millimeters in spoke length.