Brian7581

Spoke length gurus, I did a search on this forum and through out all of Google and found one decent thread which speaks about how to calculate spokes for paired hubs - Formula RB-210.

I used the spocalc.xls along with the paired spoke calculations in the top right to figure out the spoke lengths. Unfortunately, I bought spokes and they seem a lot longer than they should be when I installed them.

I have an Araya CTL-370 rim which has an ERD of 611. I measured the hub specs and they are the following:

WL - 36.4
WR - 17
dL - 47
dR - 47
Spoke diameter - 2.5

I am attempting to do a 3x with this (which I know is possible). My spoke lengths came out to 304 for the non-drive side and 302 for drive side.

I originally used 306 and 304, which was my calculation from another thread to measure the distance C-C from a paired holes closest to each other. Then measure the distance C-C from paired holes furthest to each other. Then take half the difference and add to normal non-paired spocalc calculation.

Any help in confirming this and why my spokes seem long (when threading there is no room to thread left on the nipple).

Thanks everyone!

FBinNY 

the 302/304 spoke lengths seem much more typical for a 36h 4x wheel than a 3x wheel.

I don't know what you mean by "paired spoke calculation", but suggest you go back to spokecalc which has always been OK for me, and reenter the data, including the number of holes and make sure you get the length for 3x not 4x. The right length will be either side of 296 or so.

mrrabbit 

Damon Rinard's ERD's assume the use of a standard profile 10mm nipple - and the aim is for the top.

I wonder if you are using 12mm standard profile nipples - that's takes away 1.0 - 1.5mm of overhead.

For 12mm nipples, the ERD is closer to 608mm - aiming for the screwdriver flat of the nipple.

Go back and check...

=8-)

Brian7581

Thanks for the replies so far guys.

@FBinNY - in the top right corner of Rinard's spolcalc.xls, there's a section for paired spokes. In other words, the spokes on the hubs aren't evenly spaced from each other. They create a dog bone like shape, which allows for bladed spokes to be used. This offsets the normal calculation a bit. So instead of having 3x, you'd have to use something like 3.25x to account for the different spacing (I think this is what is being thrown off though).

@mrrabbit - very good point. I checked and the nipples are in fact 12mm. This made a pretty big jump in my opinion down to 302.8 for NDS and 301 for drive side.

mrrabbit 

Had my suspicions...

Assuming you have a supply of quality 10mm nipples (DT, Wheelsmith) and assuming the rim profile is not "too aero" you may be able to swap them in - tension up - without scratching the rim surface with the bottom of the spoke wrench.

Otherwise, it's a spoke swap or cut and re-thread.

Good Luck!

=8-)

byte_speed

Newbie wheel builder question: If he has all the parts, why not just measure how much too long the spokes he bought are and adjust from there? Then there is no question about the use of any calculation.

Brian7581

Upon doing a little more reading on nipple length, it seems though there is in fact a difference (marginal between brands) in using different size nipples that it shouldn't affect ERD?

For instance, if I used the ERD calculation method provided on sheldon brown's site, regardless of the length of the nipple, the ERD will always turn out the same.

FYI, I'm using DT Swiss Revolution spokes on the non-drive side and DT Swiss Competition on the drive side, with 12 mm brass nipples.

@byte_speed - for me, it seems a bit hard to measure how much too long the spokes are because we're talking about millimeters of difference - in my case from 306 mm down to 302, which again assumes that's even right. If we were doing radial lacing, with no crosses, measuring may be a bit easier, but lacing with crosses complicates the lengths.

Thanks for the help so far guys. Still looking for other opinions or those who have built up wheels with the Formula rear hub.

mrrabbit 

Brian:

First you must understand that ERD is the distance between the ends of opposing spokes in an ALREADY BUILT and FUNCTIONAL bicycle wheel. It is a "what worked" number. Notice, nothing about the nipple size, type of nipple, etc - just the distance between the ends of the opposing spokes in a functional wheel.

The fun part of wheelbuilding is that when it comes to ERD, you are working backwards - trying to figure out the number for a rim used in a future wheel - right now!

Nipple type, nipple size, nipple behavior with a given thread does dictate what your "what worked" ERD will be.

10mm standard profile nipples typically allow 9mm box threaded spokes to protrude 1mm past the top. Overhead of 1mm says, "Aim for the top." That's what Damon Rinard does in SpokeCalc.

12mm standard profile nipples typically allow 9mm box threaded spokes to just touch the top. Overhead of 1mm says, "Aim for the screwdriver flat." That's what myself and some others do.

16mm standard profile nipples typically allow 9mm box thread spokes to just touch the screwdriver flat. Overhead of 1mm says, "Aim 1mm below." Some folks including myself aren't to thrilled with this one - but many do get built that way.

So for example, Mavic Open Pro 700c:

10mm standard profile nipple = ERD in 604-605 range.
12mm standard profile nipple = ERD in 602-603 range.
16mm standard profile nipple = ERD in 600-601 range. (Not my cup of tea...)

But the old rule still applies, measure you own ERD's when you can - and most importantly test the nipples and actual threads you are going to use.

For example, old 10mm EDCO nipples that I ran into in the late 80s and early 90s were very restrictive allowing the 9mm threading to only go 1 thread past the flat. If I remember correctly, EDCO added an extra thread inside the nipple...it's been awhile...I'm getting old.

Meaure your own ERD, do your own nipple and thread test.

It's the best way to stay out of trouble...

=8-)

Brian7581

@mrrabbit

Once again, thanks a bunch for the elaborate explanation! What you mentioned previously made functional sense, but I didn't understand the technicalities, which you just clarified.

Found a way to measure the ERD here and will try when I get home:

https://i32.photobucket.com/albums/d7...asuringERD.jpg

Again, thanks for all of the help!

Brian7581

@mrrabbit - Thanks for all of your help in my original forum post.

I got the spokes recut and rethreaded to the proper size based on the correct ERD (I did my own measure and it was in fact 608 as you had stated).

I began lacing the wheel today and after finishing both sides, noticed that on both drive side and non-drive side, the spokes that cross are still too long. I've read in other posts for paired hubs that you need 4 different spoke lengths. I am beginning to see this may be true? In which case, how do I know how much shorter the other spokes should be?

Once again, thanks for all of your assistance!

mrrabbit 

Not always the case...

Make sure the paired spokes don't cross each other - but rather they leave their adjacent holes away from each other and cross the spokes of the other pairs on the way to the rim.

302.86 and 301.37 are what I calculate. 303.00 and 301.00 when rounded off.

https://www.mrrabbit.net/wheelsbyflemingapplications.php

The spreadsheet now has a tab for calculating crossings for paired spoke arrangements. I entered "15" for the degree field.

=8-)

mrrabbit 

Be back in a few hours...

=8-)

mrrabbit 

Before I take off...

Pretension BEFORE judging....long as you are able to finish the wheel WITHOUT running out of threads...then you are doing okay. Spokes will vary within the nipple a 1/2mm either way when done.

=8-)

Brian7581

303 and 301 is exactly what I got them cut down to.

Whoops, I did cross the paired spoke holes by following a traditional 3 cross lacing.

I think crossing it the other way should fix the problem.

Thanks again so much for your insights. Has been a good learning experience. =)