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Should I worry about uneven spoke tension?

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Should I worry about uneven spoke tension?

Old 04-30-12, 05:10 AM
  #1  
Rainer Dynszis
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Should I worry about uneven spoke tension?

Hello,

I just received a new mountain bike sporting a Mavic Crosstrail wheelset.

The wheels do seem reasonably true, but I suspect the spoke tension is uneven: When you pluck the spokes like a harp, the pitch is all over the place.

If you compare only the spokes on either the left side or the right side of the hub among each others, then the difference from the highest to the lowest pitch is about four semitones.

I am unsure whether I run the risk of torn spokes if I leave it that way. What do you all think? Is it advisable to true the wheels such that the spokes will sound somewhat equal in pitch?

Thanks
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Old 04-30-12, 07:07 AM
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Kimmo
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Four semitones doesn't seem too bad. That's what, +/-16.7%, amirite?

The important thing is that they're tight enough, and the rim's round. Sure, you want even tension especially on new rims, but do you know what you're doing?

Might be worth practising on an old wheel before trying to improve new ones.

Although if the spokes seem loose, you might try adding 1/4 turn at a time to each spoke, with a bit less on the tighter ones and vice versa.

Last edited by Kimmo; 04-30-12 at 07:12 AM.
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Old 04-30-12, 07:27 AM
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It's a new bike? Take it back to the LBS and have the wheel tensioned properly.
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Old 04-30-12, 07:38 AM
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Rainer Dynszis
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Originally Posted by Kimmo View Post
Four semitones doesn't seem too bad. That's what, +/-16.7%, amirite?
Not quite. Four semitones difference lie, for instance, between E and G sharp. The frequency ratio is more like 1.26 : 1, and then I just read here that the tension correlates with the pitch squared. This means that the tension difference is more like 59% (i.e. 1.26^2).
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Old 04-30-12, 07:42 AM
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Exponential, huh?

Well I guess that means most any discernable pitch variation is a bad thing then.

BTW, I was just figuring 4/12=1/3 and /2 for the +/-.
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Old 04-30-12, 07:43 AM
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Rainer Dynszis
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Originally Posted by rdtompki View Post
It's a new bike? Take it back to the LBS and have the wheel tensioned properly.
I would probably do that if it came from the LBS, but it doesn't. Thanks anyway: I understand that in your opinion, I should not leave it as it is, right?
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Old 04-30-12, 07:56 AM
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Hey, if you're reasonably trustworthy with a spanner - actually, that seems riduculously condescending when addressing a German, somehow...

Have at it, man!

Loosen the spokes until you can see the thread just starting to show, and then tighten them all a couple of turns or whatever, then continue adding tension by small increments of 1/2 or 1/4 turn at a time until it's nice and tight, so when you grab two pairs of spokes and squeeze them with your hand, it hurts, and all kinds of pings and ticks come out of the wheel at first, until you've worked your way around it a bit. I go around the twice, and it shags my hand. Don't go too tight, or you'll potato-chip it. But you'll feel the nipples complaining before you get that far. Don't go quite so far you feel the nipples start to cop it, and that should be about right, IMO. I like to do everything up to here without the tyre on the rim.

Then make sure the tyre's at it's normal pressure since, bizarrely, it affects spoke tension. On the rear you're going to need to use a bit of trial and error to get L/R balance correct, by flipping the wheel to check it. Flip the front too, to make sure it's spot-on.

Do a final true and add more tension if you think the wheel can comfortably take it. Go for a roll on the wheels and heel the bike hard over underneath you each way as you stand on the pedals. Job done.

Last edited by Kimmo; 04-30-12 at 08:04 AM.
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Old 04-30-12, 10:10 AM
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The wheels do seem reasonably true, but I suspect the spoke tension is uneven: When you pluck the spokes like a harp, the pitch is all over the place.
'True' is only one aspect of a well done wheel build. And you did not mention if you are referring to both radially and laterally true or just one or the other. Both are important.
The uneven tension is however a major sin. I for one, would not tolerate that major defect. If left will likely contribute significantly to spoke failure via metal fatigue.


I am unsure whether I run the risk of torn spokes if I leave it that way. What do you all think? Is it advisable to true the wheels such that the spokes will sound somewhat equal in pitch?
It is as stated above 'a major sin'. Spokes on the same side of a wheel which is built to last will be at least within 20% of equal tension and likely closer. Not only nearly equal tension but the rear drive side and front disk brake side should be at a relatively high tension. The actual value is mostly determined by the rim manufacturer. I usually built to around 110Kgf. That you cannot really judge by sound (at least I can't). You, IMHO, need a tensiometer for that. Some feel they can do it by ear but....

You put a lot of trust in the wheels you ride on and depending on your style of riding put them at more or less risk. They should be trued, tensioned and stress relieved properly to the highest of standards or you risk more than your wheels.
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Old 04-30-12, 11:28 AM
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Keep an eye on it .. have what ever LBS you like most do occasional truing
if you are not a DIY wheel person.
maybe get a couple spare spokes of identical length and style.
just in case..
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Old 04-30-12, 11:34 AM
  #10  
Rainer Dynszis
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Originally Posted by Kimmo View Post
Hey, if you're reasonably trustworthy with a spanner - actually, that seems riduculously condescending when addressing a German, somehow...
LOL This line of thought is so completely alien to me that it took me quite some time to understand what you were saying here.

At first I thought you were somehow joking about the fact that "spanner" is also a german word, albeit with a completely different meaning.

Originally Posted by Kimmo View Post
Have at it, man!
I guess I should. I'd just rather avoid loosening all spokes so as to go back to square one...
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Old 04-30-12, 11:34 AM
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Originally Posted by wmodavis View Post
'True' is only one aspect of a well done wheel build. And you did not mention if you are referring to both radially and laterally true or just one or the other. Both are important.
Well, in both aspects they are true enough to not insult the naked eye.

Then again the rhythmic scratching of a plastic gauge against the rim reveals that they aren't perfect laterally. (I just found out that cable fasteners tied around the chainstay or the fork make excellent makeshift gauges .)

Originally Posted by wmodavis View Post
The uneven tension is however a major sin. I for one, would not tolerate that major defect. If left will likely contribute significantly to spoke failure via metal fatigue.
I understand that's pretty much exactly what I suspected.

Originally Posted by wmodavis View Post
You put a lot of trust in the wheels you ride on and depending on your style of riding put them at more or less risk. They should be trued, tensioned and stress relieved properly to the highest of standards or you risk more than your wheels.
Now for the practical aspect: If the wheel is reasonably true now, it probably won't be true anymore after I evened the tension, regardless of whether I go by ear or by tensiometer.

On the other hand (like I said to Kimmo) I'd rather not go back to square one and loosen all spokes, or is that the easiest way to go?
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Old 04-30-12, 11:38 AM
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Always true: Even spoke tension is more important than trueness.
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Old 04-30-12, 11:39 AM
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Bring the wheels to a LBS and have them do a true/tension on them. For a newly built wheel that hasn't had its final lateral/radial/dish/true done but is otherwise complete and not bent, my LBS will charge about 20 dollars to finish the wheel. For a simple true, its less than that.
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Old 04-30-12, 11:55 AM
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You could leave as is if you like but it would be wise to start saving for a rebuild or new wheels.
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Old 05-01-12, 08:51 AM
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With an undamaged rim, the odds are high that a painstaking approach will give you a better-built wheel than you started with.

Even a beginner can do better than a professional who's in a hurry. You care a lot more, and you can take your time.

How many spokes are we talking?
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