Spoke tensions - a bit worried

[lulubel]

I recently got myself a spoke tension meter so I could check the spoke tensions on the new wheels I've been building, and see if they're anywhere near the same. I'm near enough tone deaf (or so I thought) so didn't want to rely on the "tone" method.

The rear wheel was a bit of a disaster when I first tried building it, and I couldn't get the damn thing true however hard I tried, so I'd given up on it and decided to start again when I got the tension meter, so I could at least start the truing process with fairly equal tensions on each side. I've done that today, and my wheel now has equal tensions, and is ready to start truing.

Next, I decided to check the tensions on my front wheel (which is true in every direction) to see how close I'd got. I'm obviously not as tone deaf as I thought because all the spoke tensions were within less than 5% variance - probably closer to 2 or 3%. I'm actually rather proud of myself.

The worry is that they're registering 26 on my Park Tools meter, which is off the scale for 1.8mm spokes. The next reading down (25) is 167kgf or 1638N. My rims are rated to 1200N max.

I'm not sure what to do. The wheel is true, it wasn't starting to go out of true as I was tensioning (which I read is a sign of over-tensioning), and the spokes don't feel that tight - they give slightly when I squeeze them. Everything I've read says, most wheels go out of true because they're not tensioned enough, and one of the most common mistakes new wheelbuilders make is not tensioning enough. I find it hard to believe I've over-tensioned this wheel, but at the same time, I don't want to be doing 40mph and have the rim fail on me.

I wonder if I should put a tyre on it and pump it up to normal running pressure, and check the tensions again then. They reduce when you put the tyre on, don't they? Or do they increase? I can't remember!

 

[lulubel]

Hmm ... replying to my own question.

I've just gone round checking spoke tensions on our other road wheels. My old rear wheel and my OH's rear wheel are the same - identical bikes - (I can't use my old front wheel for comparison because it's broken). Mine, with the tyre deflated, has spoke tensions ranging from 26 - 28 on the Park guide, which translates to a maximum of 173kgf. My OH's, with the tyre inflated, has tensions from 21 - 23, I haven't got the chart handy for the kgf. So, inflating the tyre reduces the reading on the Park guide by about 5, which would put my new wheel down to 21, and within manufacturers tolerance, as marked on the rim. (After looking at the max tension marked on the rim, and doing the conversions, 21 - 22 was what I was aiming for on the Park guide.)

Also, the highest tension on my old wheel, with its cheap Alex rim, is 173kgf. Surely, my beautiful DT Swiss rims are designed to take at least as much tension as cheap Alex rims, aren't they?

 

[Davidc]

You're not alone. When I first started rebuilding my own wheels (back in the dark ages) I got my mentor to measure my first effort. I'd done exactly what you describe, perfectly true wheel with excessive tensions. In those days rims were steel, and probably more tolerant. The spokes weren't. I re-did the wheel with sensible tensions, and over the next couple of months the spokes kept breaking at the top of the bend, about 1mm from the rim. replaced all of the spokes and all was well.


It's likely that modern spokes (good ones like swiss) are better than the 1970s ones, but if the problem starts it may be worth acting quickly.

I don't do my whels any more (laziness), but the last time I did I used a chart of note against tension and measured the frequency with a microphone, laptop, and a bit of test software.

 

[lulubel]

It's likely that modern spokes (good ones like swiss) are better than the 1970s ones, but if the problem starts it may be worth acting quickly.

From what I can gather - this is from Park Tools, I think - the spokes should be fine. As you say, they're probably better now. Either that, or rims have become weaker as they try to reduce weight. In any case, the instructions on the tension meter said the rim is generally what sets the limit on spoke tensions, so it was the figure on the rim I was going with.

I'm leaning towards putting a tyre on it, and seeing what happens when I get some pressure in it. If my tests on other wheels are anything to go by, it should reduce the tensions to within the recommended limit, so I can't see that using it will do any harm at that point. If there's damange, I think I've already done it.

I don't know anyone who can take a look at it for me, unfortunately, or that's what I'd do.

 

[albion]

Spoke tension makes little sense unless the engineer tolerances of both the hub and rim are incredibly exact.
Unless you are Cavendish and get the pick of the crop surely tensions will vary from spoke to spoke.

 

[lulubel]

Spoke tension makes little sense unless the engineer tolerances of both the hub and rim are incredibly exact.
Unless you are Cavendish and get the pick of the crop surely tensions will vary from spoke to spoke.

Uh?