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Spoke pitch frequency

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Old 04-18-15, 03:39 PM
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mooder
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Spoke pitch frequency

Hello all,

I came across this:
Bicycling - Wheelbuilding: check spoke tension using musical pitch

If the tension of the two laced spokes is approximately the same, as it should be, you will hear a single, clear musical note. In a typical 700C three-cross wheel, this should be an G with plain-gauge spokes and an A with butted spokes.
Using the android app G strings (yea bad pun with G standing for guitar) most spokes of a front wheel I trued are around 100Hz. Some dip in the 50-60 ish and some in the 200 (too tight).

What does G & A stand for in frequency? G = 98Hz? A = 110Hz?

For my front wheel, what would be the correct frequency per spoke (R500 - 10 spokes each sides)?
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Old 04-18-15, 04:45 PM
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There is an iPhone ap that will relate the pitch right back to a tension, but you need to enter the spoke gauge, the crossing spoke must be damped too, I was not really confident in the results :-).

id say buy a park tension meter , I got one to build a wheel , and just used today it because I had a few loose spokes on my Sportiff, a disk brake front wheel (you did not specify if yours is or is not ) might have different tension on the two sides just like a rear wheel does.
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Old 04-18-15, 04:59 PM
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While matching pitch can be an effective way to compare spoke tensions within the same wheel, (or same flange) it's not reliable for measuring absolute tension since the pitch is a function of spoke gauge and free length along with tension.

There's no such thing as a "typical 700c 3x wheel", unless you limit yourself to ones having shallow depth rims, small flange hubs and 14g plain gauge spokes. Then there's the issue of the "right" tension for front, rear right side, and rear left side, and of course factor disc brakes, and rear axle width.

So sound is a useful tool, but like any other tool, requires some skill and understanding to be used correctly.
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Old 04-18-15, 05:39 PM
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My cousin, John S Allen, wrote a Bike World article about this method of spoke tension checking in something like 1981. But that was when spokes were round. Andy.
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Old 04-18-15, 07:05 PM
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Spoke pitch is more useful in comparing relative tensions among spokes than in determining absolute tension of individual spokes.
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Old 04-18-15, 07:55 PM
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The thing is that the spoke tension meter made by park tool is like 90$
Surely a nice tool to have for those of us doing the maintenance ourselves but in the amazon comments many user were saying it was practically useless and they could do a good / faster job by pitching the spoke.
I am willing to spend the money on one but it's somewhat uber expensive for what it is (as always with park tools).
http://www.amazon.ca/Park-Tool-Spoke.../dp/B000OZDIGY
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Old 04-18-15, 08:11 PM
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This is one of those "buy it if you want it" but you probably don't need it. It's a matter of deciding what your objectives are and considering alternatives.

I've been building wheels for nearly 50 years, and never bothered with tension measurement except by feel. I now use a tension aguge from time to time, just to cross check my fingers' calibration. So far it's usually only confirmed what I'd already guessed, though sometimes I'd find I was drifting low or high and use it as a guide to get back on track.

But I've never used a tension meter to achieve equal tension. That's done by sound and feel, which is far, far faster.

So if you simply want to compare spoke to spoke tension within the wheel, save your dough. But if you want to know the actual tension and have no frames of reference, then sound will get you into the ball park. I believe there are even smart phone aps that allow for various spoke combinations, and they should certainly get you pretty close.

But as I said, buy it if you want it.
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Old 04-18-15, 09:12 PM
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Originally Posted by FBinNY View Post
While matching pitch can be an effective way to compare spoke tensions within the same wheel, (or same flange) it's not reliable for measuring absolute tension since the pitch is a function of spoke gauge and free length along with tension.
The part that is often missed is that since maximal spoke tension is proportional to cross sectional area which corresponds to mass per unit length, you can replace the mass per unit length in the pitch equation with a constant, so pitch at maximal tension becomes

F1 = K.SQRT(T) / 2L

where T is spoke tension and L is spoke length.

Since there's less than 6% difference between common 700C spoke sizes there's less than a semitone of pitch variation amongst them at maximal tension.
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Old 04-18-15, 09:27 PM
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Originally Posted by Mark Kelly View Post
The part that is often missed is that since maximal spoke tension is proportional to cross sectional area which corresponds to mass per unit length, you can replace the mass per unit length in the pitch equation with a constant, so pitch at maximal tension becomes

F1 = K.SQRT(T) / 2L

where T is spoke tension and L is spoke length.

Since there's less than 6% difference between common 700C spoke sizes there's less than a semitone of pitch variation amongst them at maximal tension.
You're right that the same pitch will translate to tension in proportion to spoke diameter. And many old timers including myself will factor diameter, in setting our target tensions, but most builders today don't, and try for the same tension range regardless of the spokes used. Moreover, old timers that do factor gauge tend also to factor rider weight and other variables, so there's no magic number or pitch, though there's room in the ballpark.
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Old 04-19-15, 02:09 AM
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Kiu
Originally Posted by mooder View Post
..in the amazon comments many user were saying it was practically useless and they could do a good / faster job by pitching the spoke.
Pitch is fast and fairly easy for comparing spoke to spoke, but it's a lot harder to use it to determine WHICH tension you're building to.
Likewise, w/o a tensiometer, it's hard to know how close in pitch you need to get it to be good enough.
I've never regretted buying one and use it frequently.
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Old 04-19-15, 03:03 AM
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https://itunes.apple.com/us/app/spok...518870820?mt=8
I use that iphone app and I think it's excellent. What's the problem with it again?
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Old 04-19-15, 09:18 AM
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Started playing Guitar in the 60s , Mandolin in the 70's, I just used my common sense, building wheels .. and had felt what most other finished wheels seemed like.
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Old 04-20-15, 07:39 AM
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Originally Posted by mooder View Post
The thing is that the spoke tension meter made by park tool is like 90$
Surely a nice tool to have for those of us doing the maintenance ourselves but in the amazon comments many user were saying it was practically useless and they could do a good / faster job by pitching the spoke.
I am willing to spend the money on one but it's somewhat uber expensive for what it is (as always with park tools).
http://www.amazon.ca/Park-Tool-Spoke.../dp/B000OZDIGY
I bought the Wheelsmith years ago when I started building my own and friends' wheels. It's great for ultimate tension and matching tension of the spokes. I don't do it for a living, so it is not an every day job.
If you don't think you will build many don't bother.
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Old 04-20-15, 10:10 AM
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Originally Posted by mooder View Post
What does G & A stand for in frequency? G = 98Hz? A = 110Hz?
G and A are the names of the corresponding musical pitch (A, B, C, D, E, F, G). In this case the "A" is actually "A2" - a pitch two octaves below (1/4 frequency) A4 (also called A above middle C). A4 = 440Hz is the tuning standard that has been in use by the music industry for nearly the last century. But exactly how the other musical pitch names corresponds to a frequency is a surprisingly complex subject.
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Old 04-20-15, 12:20 PM
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I USE AN APPROXIMATION OF THIS METHOD IF I HAVE A SLIGHT BUCKLE ON THE RIM.Usually after hitting a bad rut or kerb. Slight damaghe to the straightness of the rim locally will need increased tension or decreased tension on the other side to pull it straight. The musical pitch will change. As long as it`s within certain limits, it`ll be fine.

To determine the limit, try pinging the spokes on the back wheel, gear side. There is tremendous tension there to compensate for lack of leverage. Any snapped spokes will occur here. And it`s a an absolute bugger to change `em . . .! Dunno why they don`t just put more spokes on that side . . . heck, I could do that myself . . .I`ve got 32 to play with . .
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Old 04-20-15, 12:36 PM
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I don't use a tensiometer when building wheels, and I generally don't use pitch, either. I just use feel. My question is: how much pitch variation is OK? I got as much as a minor third (musically speaking) difference between the lowest pitch and the highest pitch I found in the wheel I built most recently.
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Old 04-20-15, 03:11 PM
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interesting. I'm going to play around with my guitar tuner tonight!
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Old 04-20-15, 03:16 PM
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Originally Posted by mooder View Post
The thing is that the spoke tension meter made by park tool is like 90$
Surely a nice tool to have for those of us doing the maintenance ourselves but in the amazon comments many user were saying it was practically useless and they could do a good / faster job by pitching the spoke.
I am willing to spend the money on one but it's somewhat uber expensive for what it is (as always with park tools).
http://www.amazon.ca/Park-Tool-Spoke.../dp/B000OZDIGY
I got mine from Bike Hub Store for $72 USD :-). I guess I am just a tool using animal by nature, after 40+ years of buying Micrometers and Dial Indicators, and lathes and Milling Machines...72 was not a HUGE pile of $$ :-). Brandon said he bought a pile of them for a good price, hence the nice price :-)
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Old 04-20-15, 03:25 PM
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Originally Posted by noglider View Post
I just use feel. My question is: how much pitch variation is OK? I got as much as a minor third (musically speaking) difference between the lowest pitch and the highest pitch I found in the wheel I built most recently.
Tension increases as the square of frequency, so a minor third is about a 40% difference in tension. Certainly more than I like to see on my builds (unless we're talking DS vs. NDS).
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Old 04-20-15, 03:27 PM
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Originally Posted by Kopsis View Post
Tension increases as the square of frequency, so a minor third is about a 40% difference in tension. Certainly more than I like to see on my builds (unless we're talking DS vs. NDS).
Oh, good point about DS/NDS. I don't remember now, and the wheels are upstate, where I can't reach them until the weekend. What is a good guideline for maximum pitch deviation? Or am I asking the wrong question?
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Old 04-20-15, 03:57 PM
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Originally Posted by noglider View Post
Oh, good point about DS/NDS. I don't remember now, and the wheels are upstate, where I can't reach them until the weekend. What is a good guideline for maximum pitch deviation? Or am I asking the wrong question?
A minor second is about a 12% tension difference. A major second is about 26%. How much is too much depends on the build. With rims that start relatively true (untensioned) I can generally get all spokes on a side within 20%.
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Old 04-20-15, 04:03 PM
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What's the definition of a minor second? Two piccolos playing in unison.
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Old 04-20-15, 05:04 PM
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Originally Posted by Gresp15C View Post
What's the definition of a minor second? Two piccolos playing in unison.
How do you get two flutes to play in unison? Shoot one. How do you get one flute not to play out of tune? Shoot the other one.

To answer the OP's specific question, what frequency is A or G? Concert a for tuning an orchestra is (nowadays) 440Hz. An octave lower would be 220, another octave lower would be 110, etc. G's would be similar, according to the table you linked.

So I bet the author of that article was referring to A=110 and G=98; it's pretty unlikely that your wheel is off by a whole octave unless it is seriously jacked up.
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Old 04-21-15, 06:11 AM
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@Kopsis, thank you. I'll see if I can get tension within one major second. Maybe I'm there already.
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Old 04-21-15, 06:49 AM
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I'm a 30+ year musician with a good ear and I've found pitch alone to be misleading when checking spokes.

Not sure what all factors play into it, but I've found that two different spokes can be at different pitches and still measure out similarly on my Park tool.

I do regularly spin the wheel and let my thumbnail strike the spokes and listen for differences and then check there.
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