REVIEWS DEALS BIKESHOPS TRAILS

Spoke length double check please!

996 Views 14 Replies 5 Participants Last post by meltingfeather, Jan 19, 2010

PissedOffCil

Discussion Starter · Jan 14, 2010 (Edited)

Hello,
I'm about to place an order for spokes for 3 wheels. Yes three! I'm building a wheelset and changing the rim on a rear wheel. So I'm placing the order through CRC which sends the spokes with 14mm nipples (keep this in mind). Here are the specs for the 3 wheels :

1) Shimano XT FH-M756 rear hub with Mavic XM819 Disc rim
2) Hadley 20mm through axle front hub with Stan's Flow rim
3) Hadley 135mm through bolt rear hub with Stan's Flow rim

I used Roger Munson's method for compensating for longer nipples (-1 mm for 14mm nipples), all laced 3 cross, 32 holes, with DT comp 1.8/2.0 spokes.

I intentely omitted the specs I used because you would obviously get the same results if you used those. Anybody care to tell me which length you end up with?

Thanks in advance!

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Speedub.Nate

· #2 · Jan 15, 2010

Two questions:

Did you measure the rims' ERDs and get different values than what's published?

Did you run your numbers through two different spoke calculators and get similar lengths from each?

Maybe if I get really, really bored at work tonight I'll look up and run your numbers. Can I build your wheels for you, too? I'll be happy to pay the postage both ways.

PissedOffCil

Discussion Starter · #3 · Jan 15, 2010

Hehehe no you can't build my wheels...

I didn't measure the rim's ERD, I don't have them yet...

I did run multiple calculators and got roughly the same thing but I don't trust DT Swiss's calculator that much...

My point is mostly that whatever calculator you use you'll get roughly the same numbers. But are the plugged in numbers alright??? Hence, why I didn't mention them!

PissedOffCil

Discussion Starter · #4 · Jan 15, 2010

I can feel your boredom all the way up here...

Come on get that calculator out and spit those numbers, you can do it!!!

Ventanarama

· #5 · Jan 15, 2010

PissedOffCil said:
I can feel your boredom all the way up here...

Come on get that calculator out and spit those numbers, you can do it!!!

I use 12mm nipples and on the Hadley set I use 259/260 front, 258/260 rear.
XT/819 I come up with 256/258.

Larry
www.mtnhighcyclery.com

Speedub.Nate

· #6 · Jan 15, 2010

Ventanarama said:
I use 12mm nipples and on the Hadley set I use 259/260 front, 258/260 rear.
XT/819 I come up with 256/258.

Using the 14mm nipple rule -- the Hadleys I got 256/257 front, 258/256 rear.
XT/819 I came up with 258/257.

But I'm tired as a dog and don't trust my numbers enough that I'd re-run them after some rest as a double-check.

How close are we, Cli?

PissedOffCil

Discussion Starter · #7 · Jan 15, 2010

I got 256/256 for the XT, 256/258 for both Hadleys...

As previously mentionned, that was by removing 1mm for 14mm nipples and rounding "mostly down" (unless it was very close). I got 257 exactly for the XT left so rounded down to 256 to match the availabitlty at CRC. The 258 on the Hadleys we're around 257.5+ so rounded to 258.

Should it be fine?

The XT values should theoretically be fine sine the rim's ERD is 6.5mm smaller than the XC717 it replaces. Adding the -1mm nipple compensation we end up with 4mm shorter spokes and the old ones were 260. Am I right here?

PissedOffCil

Discussion Starter · #8 · Jan 15, 2010

Nate???

These are the exact numbers I got :
XT left = 257
XT right = 255.6

Hadley front left = 257.6
Hadley front right = 256.7

Hadley rear left = 257.9
Hadley rear right = 256.5

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Speedub.Nate

· #9 · Jan 16, 2010

Sorry, I didn't think you were waiting for a reply.

There comes a time when you just have to place your order. Each spoke calc I use comes up with slightly different results. You, Larry and I all came up with similar results. Larry is indicating he's built wheels using his numbers, so that lends credibility to his results.

In general, you've safely got +/- 1mm of variance you can play with without running into trouble.

PissedOffCil

Discussion Starter · #10 · Jan 16, 2010

I'm aware of all this but it's nothing short is very unpleasing to get the wrong length spokes and not being able to build the wheel...

Speedub.Nate said:
Sorry, I didn't think you were waiting for a reply.

There comes a time when you just have to place your order. Each spoke calc I use comes up with slightly different results. You, Larry and I all came up with similar results. Larry is indicating he's built wheels using his numbers, so that lends credibility to his results.

In general, you've safely got +/- 1mm of variance you can play with without running into trouble.

Larry, did you measure the 819 with 12mm nipples as well? It's suppsoed to be a PITA to build them with 12mm nipples... Mind to give me the exact (not rounded) lenght you came up with?

meltingfeather

· #11 · Jan 19, 2010 (Edited)

PissedOffCil said:
I don't trust DT Swiss's calculator that much...

DT's calculator is bullet proof if you put in good numbers. It's the database that is spotty. They can't keep up with all manufacturers' models, changes, etc. They seem to have omitted that problem by doing away with the database. What probably started out as a good willed attempt to be the most helpful (including other mfr info) got the calculator a lot of criticism. I had a tech service guy at Mavic tell me that the DT Swiss calculator is wrong. Pretty ballsy from a guy at a company who decided to go their own way (and out of the way) and use wheel building specifications that are seemingly willfully counterintuitive and confusing. Your distrust of the calculator is probably based on the same misinformation. The database is really separate from the calculator, but people meld the two.
The math is very simple.
You may notice that Roger's calculator does not have an input for spoke hole diameter. What that means is that he's either ignored it and used length to the center of the spoke hole, or assumed some value. That is one source of discrepancy between Roger's calculator and others.

PissedOffCil said:
My point is mostly that whatever calculator you use you'll get roughly the same numbers. But are the plugged in numbers alright??? Hence, why I didn't mention them!

Good luck. You'll probably be fine. I happily run numbers for people as a double-check, but I'm not about to duplicate the research leg work. It was a pretty ambitious question.

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Speedub.Nate

· #12 · Jan 19, 2010

...and yet inaccuracies in spoke hole diameter have as big an impact as inaccuracies in ERD. Could never figure you why Shimano goes to re trouble of listing flange offsets to the hundredths, but often fails to list spoke hole dimensions.

meltingfeather

· #13 · Jan 19, 2010

Speedub.Nate said:
...and yet inaccuracies in spoke hole diameter have as big an impact as inaccuracies in ERD. Could never figure you why Shimano goes to re trouble of listing flange offsets to the hundredths, but often fails to list spoke hole dimensions.

True, though the range for the variation is much smaller.
I believe Shimano uses 2.6mm SHD in all their hubs... though not 100% on that. If you call them, they'll give you all the answers you want.

roger-m

· #14 · Jan 19, 2010

meltingfeather said:
You may notice that Roger's calculator does not have an input for spoke hole diameter. What that means is that he's either ignored it and used length to the center of the spoke hole, or assumed some value. That is one source of discrepancy between Roger's calculator and others.

My calculator is written in Javascript and here is the line that does the spoke length...

Code:

sl=sqrt(r*r+h*h+f*f-2*r*h*cos(720/holes*cross*2*PI/360))-2.9/2

I use a spoke hole diameter of 2.9mm which is on the high side but there's nothing scientific going on here, all I did was change the diameter until I was happy with the resulting figures i.e. I obtain good real world spoke lenths for all the wheels I build, from BMX to road.

meltingfeather

· #15 · Jan 19, 2010

roger-m said:
My calculator is written in Javascript and here is the line that does the spoke length...

Code:

sl=sqrt(r*r+h*h+f*f-2*r*h*cos(720/holes*cross*2*PI/360))-2.9/2

I use a spoke hole diameter of 2.9mm which is on the high side but there's nothing scientific going on here, all I did was change the diameter until I was happy with the resulting figures i.e. I obtain good real world spoke lenths for all the wheels I build, from BMX to road.

Interesting! I actually tried to duplicate numbers out of your spoke calculator once and concluded that you must have been using a high number for the SHD... forgot totally about that. It could easily be seen as a bit of an empirical correction for spoke strain, which your calculator does not otherwise appear to account for.
Thanks for offering that up. :thumbsup:

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