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Mix 'n Matching spokes gauges?


kosmonooit
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CRC sent me two different spoke gauges for different lengths with the order I made with them. I ordered Competition which are 2mm-1.8mm, they supplied the one length these, and the other length Revolution which are 2mm-1.5mm. Its to build a ZTR Flow rim on a Project 321 Lefty hub.

 

I managed to build the wheel and true it, but having doubts if this its wise to use as is. I found I had to tension the Revolutions more to get the rim centred, but really cant face another two+ week delay getting more spokes from CRC, and getting them locally, well don't seem to have any options here (Price, lead time, and long faces from bike shops who don't like supplying parts to DIY'ers)

 

So thinking about this mechanically: should be okay? maybe not.. although I have not been able to measure tensions,so cant say the one side is over-tensioned but ... but a chain is as strong as its weakest link. Being a perfectionist, I would like the bike a 100% and not a hotch botch. Its for my All Mountain build so might be getting a bit of airtime with this machine.

 

I have also read some build wheels with a mix of spokes, though reason was not stated.

 

Any thoughts on this from the collective wisdom that is thehub?

Edited by kosmonooit
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Mixing spoke gauges is OK, provided you're not putting rubbish spokes into the mix, such as straight-gauge spokes.

 

The spokes you have there are fine.

 

The only reason you had to tension the Revos more is because they're on the dished side of the wheel. It has nothing to do with their thickness. The wheel just sees tension, not how thick the spokes are that are providing the tension.

 

There is almost zero chance that you can overtension a wheel with Revolution spokes and a 890% chance that you can undertension them. This is simply because of their propensity to twist. The resistance to twist (torsioinal rigidity) goes up with the square of the surface area of the rod. Therefore Revolutions, although just a little bit thinner than Competitions, have double the propensity to twist and it is impossible (or just about) to get them to overtension.

 

Provided that everything else in your wheel is good, the combination is fine.

 

You talk abou the weakest link - in this case it is ironocally not the Revolutions but the Competitions.

 

Go ride, and screw bike shops that sneer at DIYers.

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Thanks JB, will do. I'll get used to the mismatch.

 

I have noticed the tendency of the Rev's to twist, and used padded pliers to hold them so they don't twist. But raised another question: surely with twisting spokes, this introduced metal fatigue and structural weakening?

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Thanks JB, will do. I'll get used to the mismatch.

 

I have noticed the tendency of the Rev's to twist, and used padded pliers to hold them so they don't twist. But raised another question: surely with twisting spokes, this introduced metal fatigue and structural weakening?

 

You cannot hold them to prevent twist. No such tool exists and a padded plier will only fool you. You have to put a white mark on each spoke and manage the twist. This you do by overshooting and then turning back - I'm talking about the spoke spanner now.

 

As long as you twist them within their elastic limit, you won't weaken them. However, if they're deformed plastically and then tensioned, they break very quickly with a characteristing circular pattern in the cut-through. Metal doesn't take kindly to torsion and tension simultaneously.

 

Metal fatigue doesn't come into play during wheel building.

Edited by Johan Bornman
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Thanks - to my knowledge I did stop the twisting, I could hear the difference, and was able to tension up the spoke and get some results. Perplexed me for a while until I resorted to that. I used the inside of the jaw of those adjustable pliers, with a fold of a SRAM doc that comes with their goodies.

 

What I mean by fatigue: surely with twisting it cant be a good thing for the metal the spoke ... what is the prescribed limit to the number of twists over a 26" spoke?

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Thanks - to my knowledge I did stop the twisting, I could hear the difference, and was able to tension up the spoke and get some results. Perplexed me for a while until I resorted to that. I used the inside of the jaw of those adjustable pliers, with a fold of a SRAM doc that comes with their goodies.

 

What I mean by fatigue: surely with twisting it cant be a good thing for the metal the spoke ... what is the prescribed limit to the number of twists over a 26" spoke?

 

Fatigue is the result of repeated elastic deformation below the yield point. This means that the metal never takes on a new form but flexes/stretches to below the point where the change is permanent. Depending on the type of metal and how close each cycle gets to yield, the point where fatigue sets in and the metal crystals separate (crack), could be after a few million cycles or as little as a few hundred cycles.

 

In the case of building a wheel where you are cranking up the spoke tension and the spokes start to twist, you should never let them twist more than about 3/4 turn on a long spoke (road wheel/29er) or about 1/2 turn on a small wheel. After that point you're reaching yield and permanent set of the twist. Below that point you can twist and untwist to your heart's delight, it'll just about never fatigue.

 

There is no prescribed limit. However, if you twist it into yield whilst it is under tension, it breaks very, very quickly. Metal just doesn't like that.

 

In all my years of wheelbuilding I've never found anything that can hold a spoke to prevent it from twisting. I've bought special tools called "Twist Resisters" and whatnot. The end result is always a twist with Revolution spokes.

 

The only way to overcome the problem is to use plenty of high-pressure oil like gearbox oil, brass nipples and the overshoot-return technique with the spoke spanner.

 

Even then, you usually reach a point where you don't have as much tension as you'd like the wheel to have, yet you cannot proceed because the spoke now twists uncontrollably.

 

If like you say, SRAM manual paper inside a pair of pliers works, then I'm dropping by the papent office tomorrow.

 

My guess is that you stopped before you reached high tension and therefore the technique worked.

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