mrmb

I began to STRONGLY suspect that my tension meter was giving me readings that are far too high. So....what to do? Buy another one? Maybe that one will be off too.

I was using the tension meter and the chart that comes with it. I would shoot for the KGF spec provided by the rim manufacturer. But the spokes just felt too LOOSE after getting the desired KGF.

So I decided to check it for accuracy...



It was way off, just as I suspected. About 4 divisions high.

I tried to "calibrate" the tension meter so that the number it gives me corresponds to the actual amount of KGF present at the spoke. Nope. Not enough adjustment in the adjuster screw. So I adjusted it to read exactly 3 divisions high at all times and i confirmed that it is 3 divisions high at the entire range that is applicable. I have to subtract three divisions to obtain the real number. I can live with that.

To confirm accuracy of the load scale I hung it from a chain with a 100lb weight. It gave me a reading of 100lbs. Good enough.

3Roch

I like the test rig. Is the tension gauge new/used/second owner/old/dropped ??

I have one, now you have me worried

RGMN

You can always send the tension meter back to Park to have the spring replaced and calibrated for $10.

JohnDThompson 

That's pretty much like the tool I used to calibrate Hozan tension meters for Trek's wheelbuilders BITD, except back then we only had analog (dial) indicators.

mrmb

I thought about that. But they stay calibrated for a very short time. For about $30 and 30minutes of time you can build your own test stand and calibrate it yourself.

mrmb

Purchased new, used by me only for about 8 wheelsets. Never dropped. A few years old. It don't take much to build this. Go for it. Fun little project and very handy.

Russ Roth

I've heard previously that the park were frequently inaccurate. Its one of the nice things about the old wheelsmith meters, the tension chart was made based on the readings from the meter. Course if you lost the chart the readings were meaningless.

Andrew R Stewart 

I always felt that the tension gages were about getting a general range of consistent spoke tensions then any one amount on any one spoke. Like using a dial indicator to true rims, it's not how many thousandths here or there but how minimal the variances are. I have one of the first gen WS gages at home and use the park at work. Both do the job they can and the rest is up to the builder. Andy

mrmb

Yes, general range of consistent tension all the way around, not just 1 spoke.

And if the meter tells you that you have a consistent 190KGF you really have half that, then it's best to find a way to get readings that accurately represent the tensions within the spokes you are measuring....right?

Andrew R Stewart 

Having built wheels for years before a spoke tension gage was considered needed I guess I just don't know what I was doing with those hundreds of wheels Andy

cyccommute 

I have never seen a definitive number on recommended spoke tension from any rim manufacturer...and I have looked far and wide. Some give ranges and some give nothing but I have never found a chart that says “model XX: xxx N spoke tension”. Velocity, for example, says this

That’s about as much as I’ve ever found and it’s hardly useful since they produce many different models with many different weights and configurations. And, by the way, I’ve never seen a suggestion of 190kgf (1870N, to use a real force measurement). 1270 N (130kgf) is about the limit I’ve seen for the broad range. Park’s meter chart doesn’t even go up to 190kgf.

In reality, the “actual”...i.e. a quantifiable value...is far less important than consistent tension. Yes, there is a lower end of tension that is needed but there really isn’t “a” value that is required nor will work for every situation.

Geepig

I have often wondered what tension my spokes are, but never wondered enough to go through with it.

The Park tool looks more like a comparator than a measurement tool, something which in a traditional production environment would require regular validation.

Trakhak

I suspect that Trek bought those tension meters after fielding complaints from dealers that wheels on Trek bikes were seriously undertensioned out of the box.

I remember asking our Trek sales rep why the problem had arisen. He said that bike sales had increased to the point where they couldn't build enough wheels in house, so they farmed out their wheel building to local senior centers (presumably without accounting for the prevalence of arthritis).

mrmb

White Industries G25A rim...........120kgf. There is one rim with a manufacturer recommended definitive number.

Buuut, I get it. A wheel builder does not typically shoot for en EXACT number. Thats not the point nor was I saying that we need to shoot for a specific number. In spite of that, it is still good to be able to tell for certain that you are within the range of acceptable and one good way to do that is with a tension meter that reads accurately.

I wasnt saying anything about the existence of a suggestion of 190kgf, but rather that my park tension meter was reading wildly high, in the neighborhood of 190kgf, yet the real kgf was only about half that.

mrmb

If uncalibrated, it is a comparator.

If calibrated or compared to a known value, it is a measurement tool.

79pmooney

I use my ear for relative tensions and the Park for the overall. So the OPs news is a little disconcerting. Yeah I could build that test stand but I have lots of homemade tools that get used once or thrice a decade. I don't need more.

This does mean my Park really doesn't see a lot of use. Maybe a dozen or two times per build. But the really easy reality check is ping the spokes. Go ping a similar wheel.

cyccommute 

Recommended where? It’s not on their page for the rim. And the tension is going to be somewhat dependent on spoke gauge.

A reading of 190kgf is off the chart for the Park tension meter. On a 2.0mm spoke, for example, a reading of 28 says that the spoke has a tension of 174. I’m not sure how you calculate a reading of 190kgf since the tension measurement isn’t linear but I’ll ignore that for now. Let’s assume that the reading works out to about 30 on the meter. In my experience with the Park Tension meter on a 2.0mm spoke, a reading of 30 is an extremely, extremely tight spoke. A reading of 25 is extreme in my opinion. If you are saying that the actual tension is only 80 kgf, the spoke should be loose. A reading of 25 is dangerously close to cracking just about any rim. Much above 25 starts to result in rounded off spoke nipples as well.

I run my spokes very tight...mid 20s on drive side and front with 15 to 18 on nondrive side...and cracking is the most common type of rim failure I experience. What you are saying is that the tension reading, at the point where spoke nipples round off and rim crack, is far too low and needs to be increased nearly to the limit of the tension meter. At the reading on the meter you are suggesting...around 40...the spokes aren’t just going to crack but the spokes are going to pull through the rim during the build..if you can get a spoke wrench on a round spoke nipple.

To be clear, I’m not saying that the Park tool is highly accurate. But it’s not off by as much as you say it is.

pdlamb

Wonder if anyone's tried calibrating a tensiometer against an electronic tuner?

For that matter, could you build a jig with a bolt on one end and use a torque wrench to develop the force on the spoke (surrogate), saving the cost of the load cell?

Dan Burkhart 

Aside from the obvious design differences between the Park tool and the others in my arsenal, (Wheelsmith and Wheel Fanatyk) another significant difference is that the meter is adjustable, and every calibration chart is the same. The tool is adjusted to match the chart, whereas the others have a calibration chart that is unique to each tool and is printed after taking readings in a calibration jig.
Consequently, while the tool can be more or less accurately calibrated to a default spoke which would typically be a 2.0 mm stainless, the variances can become quite great on light gauge or aero spokes for example.
My Park tool is fairly accurately calibrated to a 2.0 stainless as can be seen in the photos below. At 100 kgf on my calibration fixture, the Park tool reads just under 24 . 24 is 107 on the chart.
I have had the Wheelsmith tool for something like 17 years, and 100 kgf corresponds to 80 on the chart. Still dead on after all these years, however when I build with bladed spokes such as CX Ray as I frequently do, I need to calibrate each time.
Another observation I would make, and I don't really know what impact this would have on accuracy is that the park tool increases the tension on the spoke to a much higher degree when taking the reading than my other meters do. A 6% increase as compared to about 1% for the Wheelsmith and Wheel Fanatyk.
In the photos you can see the heavy torsion spring and the adjusting screw on the Park tool as compared to the compression spring on the Wheelsmith. As low tech meters go, I find the Wheelsmith to be about as good as it gets.

mrmb

On the rim itself.

mrmb

25, if properly calibrated is 120kgf w/ a 2mm spoke which is in line with the tension that rim manufacturers generally say to build the wheel to. So how is 120kgf (25) extreem? Isn't the NDS tension dependent on how you dish the wheel? Shoot for a given tension on the DS then let the NDS be what it needs to be to get proper dish. Thats the approach I have been using and seems customary to many. You say Mid 20s on the DS then 15-18 on the NDS (seems pretty low....60kgf for 1.8mm...isn't that kinda loose?).

Buut, I have been shooting for 25 on the DS which comes out to 24 or 25 on the NDS with a perfect dish (no huge cassettes here). No rounding of nipples, no extreme tightness, no cracked rims and right where the rim manufacturers say tension should be. Not sure why all the "extreme talk"...

70sSanO

Since I’m not inclined to mfg this type of calibration device, I’m wondering what can be used.

I did try my park tool on an electric bass string, probably tensioned around 40 ft/lbs but it just zeroed out.

But isn’t it possible to calculate the deflection of a 1/8” or ??? steel rod or stainless rod, or square stock, and once that amount is known transfer it to a spoke tension gauge to calibrate it?

John

cyccommute 

Sorry, I misstated there. While I was discussing 2.0mm spokes, I build with triple butted spokes so the value used is for the thinner center section. A 1.8mm spoke hits about 120kgf at about 22 on the meter. The spoke “feels” very tight and any more tension tends to start rounding spokes.

Yes, the nondrive side is going to be what it is going to be but it ends up reading between 15-18 on the tension meter. That translates to a range of values from 58 to 77 kgf on the Park chart. That’s in the range of about 60% of the driveside spoke tension as would be expected with a symmetrical rim. Off-center rims would have a higher spoke tension on the nondrive side. If I measure the tension...I’m don’t always...I aim for consistent tension on the driveside as well as on the nondrive side.

I’m confused then. You are the one who said that the calibration was off by 50% and started talking about the tension meter giving 190kgf readings but really only being 80kgf. If the meter is that far off, I’d expect that “shooting for 25 on the [drive side]” the tension would be far too low for the wheel to be useful. If the meter is off by as much as you say, shouldn’t you be shooting for a much higher value on the tension meter? In my experience, any value higher than about 25 results in issues with the wheel build, depending on the spoke, of course.

To be honest, I don’t do the conversion to kilograms-force because I can’t be bothered and the actual number isn’t really all that important. Consistency is but the actual force value isn’t.

Most every tension value I’ve been able to dig up...after lots and lots of digging...has been a rather broad range for the entire range of rims that manufacturers offer. Velocity, for example, says to use 110 to 130 kgf...period. That’s for 15 different models of rims that have a wide variety of widths, weights and thicknesses. If the tension value had any real meaning, there should be a chart of tension suggestions for each model. The chart should also include tension values for every possible spoke combination as well. I would suspect that the length of spoke is going to have an impact as well.

You should be able to see that the permutations would quickly get out of hand.