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How to measure spoke tension properly?

BikeGremlin

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Wheel Wizard
A question I got on the video about wheel truing catches and gotchas:

Thanks for another great video!I have seen that for instance Park Tool in their videos have stressed that it is important to measure the spoke tension in the middle of the spoke. This is because that's where the spoke will deflect the most, since it's the furthest from the “fixed” points (the hub and the nipple respectively).If you measure the spoke closer to either end, the reading should be higher for the same spoke tension.In your opinion, is it a good idea to measure it closer to the nipples, so that it is easier to measure from the same point of the spoke (like in this video)? Or should you measure in the middle, so that different spoke lengths do no result in (too) different tension readings?I hope it makes sense…
 
Solution
This is a very good question - and answering it on the forum should help everyone find it (at the time of writing, YouTube comments can't be searched via Google as far as I know).

There are two things worth discussing: how to measure, and measurement tool accuracy and precision (two distinct aspects that overlap to a degree).

How to measure spoke tension​

I'll start by linking the "Accurate vs Precise article," and the video "Accurate vs precise, digital vs analogue - Calipers, how to use them?"

As usually, Park Tool instructions are spot on. It is more accurate to measure spoke tension as close to the middle as possible.

However, because of the spoke crossings on a laced wheel, this is as far to...
This is a very good question - and answering it on the forum should help everyone find it (at the time of writing, YouTube comments can't be searched via Google as far as I know).

There are two things worth discussing: how to measure, and measurement tool accuracy and precision (two distinct aspects that overlap to a degree).

How to measure spoke tension​

I'll start by linking the "Accurate vs Precise article," and the video "Accurate vs precise, digital vs analogue - Calipers, how to use them?"

As usually, Park Tool instructions are spot on. It is more accurate to measure spoke tension as close to the middle as possible.

However, because of the spoke crossings on a laced wheel, this is as far to the middle as my tensiometer goes on a 28" wheel laced 3 across (with smaller wheels, I can sometimes only get it close to the nipple):

Measuring spoke tension


So, especially with swagges spokes (thinner in the mid-section), to get precise results with my tool, it is important to always measure at the same distance from the nipple (which is sometimes right at the nipple) - for consistency. Such measurements are less accurate, but more precise (giving the same measurement value for the same spoke tension).

This depends on the wheel and the spokes used. I usually take a few measurements and see what gives the most consistent (i.e. most precise) measurements for the given wheel.

That is what works for me.

Having said that, the demonstrations in my video, without this context, are not good, in my opinion. I plan to make a separate video explaining the nuances (ideally with some swagged spokes).

Tensiometer tool precision and accuracy​

This is also worth discussing. The tool I use is an open patent (i.e. it is not patent-protected and anyone can make it). Whel Fanatyk are making and selling such tools (to name one that is widely known).

That tool has two pivots with bearings that eliminate friction from affecting spoke's bending, with the spring pulling on the spoke in the middle between the two pivots, and a micrometer measuring that deflection at that spot (on the opposite side - so the spring pulls the spoke towards the micrometer).

Other tensiometers don't resolve the friction problem nearly as well, so they are inherently less precise (by design). These tools get the job done, I'd say they are good enough, but their margin of error is larger, by design (i.e. less precise).

For all the tension meters, the accuracy boils down to how well the spoke's deflection is converted to (calculated) actual spoke tension. This absolute spoke tension is important because spokes that are too loose will give a weak wheel and start unscrewing, while the spokes that are too tight might result in wheel buckling under external load (or go out of true during the building process when stress-relieving the spokes after the final tensioning - which is the first telling sign that the tension is too high).

However, I'd say that accuracy is less important, you just need to get it in the ballpark between too loose and too tight (for a given rim's strength). There is quite some margin of error between the spokes being too loose or too tight. But precision is important for making sure that spoke tension is reasonably equal (acceptable tollerances).

Why other manufacturers (including Park Tool and DT Swiss) don't use the inherently more precise patent is beyond my understanding. Maybe the price would be too high for them to make many sales and high profits per unit (a high-quality micrometer itself costs more than the whole tensiometer by these manufacturers).

Final thoughts​

I am self taught. There are no wheel building (or bicycle mechanics for that matter) schools or courses in my country (not for a professional high level of expertise - some volunteers, like me, do provide some basic training on occassions). So all my articles and videso are based on my knowledge, education (from books and other mechanics), and first hand experience (i.e. what's worked well for me so far). Nothing more, nothing less.

Viewer and reader feedback has been very helpful to correct and improve things over the years. Making a tension measuring video is definitely a good idea.

Relja
 
Solution

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