Measuring straight pull hubs?

[Gummee]

I've got a pair of 26er wheels (M785 XT 28h) that I can't sell, can't find the dimensions online, and well... if I don't do something with them, they're going to keep sitting in the box.

So the thought is to rebuild em into a 29er wheelset so I can at least use them for something.

...so... how does one either go about finding the dimensions on said hubset or measuring them? I know how to find centers of regular hubs, but straight pull spokes got me

M

[oldpotatoe]

I've got a pair of 26er wheels (M785 XT 28h) that I can't sell, can't find the dimensions online, and well... if I don't do something with them, they're going to keep sitting in the box.

So the thought is to rebuild em into a 29er wheelset so I can at least use them for something.

...so... how does one either go about finding the dimensions on said hubset or measuring them? I know how to find centers of regular hubs, but straight pull spokes got me

M

785 shimano pre builts? Can ya get 29er rims from shimano and spoke kit? The 29er wheel is same hub, isn't it? But isn't the front 24h? Just looking at shimano tech docs.

[oldpotatoe]

I've got a pair of 26er wheels (M785 XT 28h) that I can't sell, can't find the dimensions online, and well... if I don't do something with them, they're going to keep sitting in the box.

So the thought is to rebuild em into a 29er wheelset so I can at least use them for something.

...so... how does one either go about finding the dimensions on said hubset or measuring them? I know how to find centers of regular hubs, but straight pull spokes got me

M

Perhaps figure out a ratio..spoke length to rim ERD for 26 inch..that number, same number for a larger ERD rim(?)I donno,not a math guy. Or get spoke length for the built 29er wheels..correct for a different ERD?

[Gummee]

Shimano sez they changed the hubs between the XT wheels I have and the replacement rims from the 29er wheels they're selling now. Talked to a guy there says 'not compatible.'

Grrr

If they weren't straight pull, I could experiment... I have a ton of j-bend spokes to try... Not so much straight pull.

M

[CiclistiCliff]

Measure erd of current rim and measure the spokes. 10mm erd change is equivalent to 5mm spoke change, from what I gather.

I have some easton wheels I reverse engineered that way and multiple spoke calcs give me the same info.

[Mark McM]

Measure erd of current rim and measure the spokes. 10mm erd change is equivalent to 5mm spoke change, from what I gather.

I have some easton wheels I reverse engineered that way and multiple spoke calcs give me the same info.

Yes, this is the way to do it. The difference in spoke lengths will be half the difference of rim ERDs.

Technically, this method will be off by a fraction of a millimeter, due to angle errors, but spoke lengths are only available in increments of 1 mm anyway.

[tellyho]

Sorry for dredging thias old thread up, but I'm having trouble finding answers on measuring straight pull hubs. Does anyone have a good way for measuring spoke offset? I can get the rest of the measurements well enough, but this one is challenging.

[Suckleyi]

Check out: https://spokecalc.io/measuring-a-straight-pull-hub.php

Should get you in the ballpark

[Mark McM]

Sorry for dredging thias old thread up, but I'm having trouble finding answers on measuring straight pull hubs. Does anyone have a good way for measuring spoke offset? I can get the rest of the measurements well enough, but this one is challenging.

What do you mean by "spoke offset"? It seems to me the hardest measurement to get is the spoke angle.

Edit:

Ah, I just took a look at the spokecalc web page referenced above. Unfortunately, the "spoke offset" dimension referenced is to a reference line, but that reference line is not necessarily at easily found physical point. In the example given, the reference line exists in the middle of the solid flange, so there is no point you can directly measure from. The ends of the spoke itself are at surface points that can be directly measured, so there should be a direct mathematic solution. I'll see if I can come up with a formula.

[tellyho]

Check out: https://spokecalc.io/measuring-a-straight-pull-hub.php

Should get you in the ballpark

Thank you; yes, I read that article and can get pretty good numbers but I'm worried that pretty good will not be quite good enough. I've built many j-bend wheels, but never straightpull.

[tellyho]

What do you mean by "spoke offset"? It seems to me the hardest measurement to get is the spoke angle.


Agreed; I'm putting these hub from a 29" wheelset into a 26" fatbike wheel. I'm assuming the spoke calculator is going to give me the right spoke lengths there, given correct inputs. I suppose I could make my own formulae, but that seems foolish.

[Mark McM]

Taking a closer look at the Spokecalc.io website, I see that their method of calculating straightpull spoke length makes some assumptions about the hub flange geometry, and will not work for all straight pull spokes. For example, it will not work with Campagnolo FTW hubs:

https://cdn.shopify.com/s/files/1/1041/1160/products/DSC_0569_320c13a8-d22a-4ceb-8b22-6d98e1f3427c_grande.jpg?v=1584117470

One piece of information missing from the Spokecalc.io method is the number of spoke crossings, which will affect spoke length. So they must be making an assumption about the spoke crossings.

[Suckleyi]

You can check out DT's spoke calc site too. If you put in one of their straight pull hubs and click the little "i" next to the box you can see what they're measuring. You could go by that and plug the numbers you get from your hubs and see what comes up. Compare those numbers with the spokecalc.io and see what you get.

DT hubs are cross specific and you'll see that when you choose a hub. I would think that most hub manufacturers would drill as DT does; for a specific cross pattern(It's very obvious the cross pattern of DT's when you insert a few spokes). Of course, I could be wrong!

I guess the obvious question is have you reached out to the manufacturer of your hub(s) to get the dimensions? I could see where that may be difficult and I'm sure you've thought of it.

I've built many, many J-bend wheels, 1000's, but very few straight pull and a little reflection tells me they've all been DT. It made spoke calculation easy.



Thank you; yes, I read that article and can get pretty good numbers but I'm worried that pretty good will not be quite good enough. I've built many j-bend wheels, but never straightpull.

[tellyho]

Thanks for the above. The hub is Roval, so sort-of DT. I suspect it's VERY sort of DT, but when I asked Spesh, they wouldn't give me the numbers. I was planning on using both DT and the io calculators to cross-reference. The original wheels were 2x, so that will be what I'll build.

[Mark McM]

Agreed; I'm putting these hub from a 29" wheelset into a 26" fatbike wheel. I'm assuming the spoke calculator is going to give me the right spoke lengths there, given correct inputs. I suppose I could make my own formulae, but that seems foolish.

Do you have the original built 29" wheels? If so, then maybe the easiest thing to do is to disassemble the 29" wheels, measure the 29" rim ERD, measure the lengths of the spokes, measure the ERD of the 26" rims, and subtract the difference in ERDs from the current spoke lengths. There will be a small sine error using this measure, but it will likely just be a millimeter or so.

[tellyho]

Don't have the originals, just the hub.

[oldpotatoe]

Sorry for dredging thias old thread up, but I'm having trouble finding answers on measuring straight pull hubs. Does anyone have a good way for measuring spoke offset? I can get the rest of the measurements well enough, but this one is challenging.

Use this and click on "spoke offset" and it will describe what it is. Select 'straight pull' at the top.

https://www.wheelpro.co.uk/spokecalc/

But easy to measure hub flange diameter and hub flange center to flange.

[tellyho]

Use this and click on "spoke offset" and it will describe what it is. Select 'straight pull' at the top.

https://www.wheelpro.co.uk/spokecalc/

But easy to measure hub flange diameter and hub flange center to flange.

Definitely agree. I can get all the other measurements. Just not sure how I'm going to measure the spoke offset - I know what it is, but not its size.

I suspect this will be the first and last straight pull hub I build with. If I'm lucky, I'll only have to buy two sets of spokes when the first is wrong :)

[ergott]

Definitely agree. I can get all the other measurements. Just not sure how I'm going to measure the spoke offset - I know what it is, but not its size.

I suspect this will be the first and last straight pull hub I build with. If I'm lucky, I'll only have to buy two sets of spokes when the first is wrong :)

First, measure the thickness of the SP flange. Then measure how far the spoke head sits in that flange (mark its depth by marking the exposed portion and measure to the head of the spoke. With a little bit of algebra, you can calculate the offset of the flange.

I found it tricky the first time. Once I could visualize what I was measuring I had a system of reliably measuring SP hubs.

[tellyho]

First, measure the thickness of the SP flange. Then measure how far the spoke head sits in that flange (mark its depth by marking the exposed portion and measure to the head of the spoke. With a little bit of algebra, you can calculate the offset of the flange.

I found it tricky the first time. Once I could visualize what I was measuring I had a system of reliably measuring SP hubs.

Thank you! Simple method, makes sense, wondering why I couldn't think of it.

[tellyho]

Wanted to post a general thanks for help on this topic. I successfully measured my hub, calculated spoke lengths and built the wheel. I was fully expecting to have to buy another set of spokes, but it worked on the first go.

I don't know that I'd choose another straight pull hub but the build was actually pretty easy. I did not have spinning spoke issues.

So, thanks all!