tFUnK

I picked up a cheap spoke tension meter for entertainment. Tried it on a few wheels and despite concerns about calibration accuracy, for the most part the numbers seemed to be within the expected ranges.

For the NDS rear spokes, I understand that the best practice is to get the tension right on the DS, get the wheel round and true, and let the NDS spokes fall where they may. On most of my wheels, the DS tension values seem reasonable and so do the NDS tension values.

However, on one wheel in particular, the NDS tension seems so low that it's barely registering on the tool, and way below the expected range. This was on a factory built wheel with less than 500 miles (and it rides fine). The company is small but has a decent reputation from what I can tell on the internet. It's a 55mm carbon clincher rim on cx-ray spokes (steel bladed 1x2mm). Measurements were taken with tube and tire on the rim at 90psi.

Is it normal for the NDS spoke tension to be so low? Even if my cheap tool is way out of calibration, having the NDS spokes barely register (and some not register anything at all) doesn't seem right. But technically it still aligns with the "tension DS, keep wheel round and true, let NDS be whatever it may be" mantra.

FBinNY 

First of all, understand that the ratio of right and left side tensions is determined by geometry. It's the same as the ratio of the center to flange distances and cannot change.

Secondly, folks are getting distracted by focusing on tension, which is at most a secondary concern. What's more important is spoke elongation, so thinner spokes can and do work better at lower tensions.

There are other considerations, so I can't advise because I lack the specific info needed. Except that I suspect that you also lack the knowledge and experience to make any kind of judgement call.

What you need to ask yourself is whether, newly armed with a tension meter, you are now smarter than the people who built this wheel.

So I suggest you follow rule #1, and don't fix what ain't broke.

CliffordK

How many spokes does the wheel have? Sometimes wheels with higher spoke count will have lower spoke tension.

As @FBinNY suggests, I wouldn't worry about it to much as long as you can feel some tension when squeezing a pair of spokes with the hand.

Lombard

Would you care to divulge which "cheap tension meter" you bought?

FBinNY 

Here's a very easy way to get an indication of a tension meter using only a ruler.

Accurately measure the CTF distances of your hub. Next measure the zigzag offset in the rim.

Subtract half the zigzag offset from each CTF. Now compare the two results and calculate the resulting ratio.

This ratio MUST equal the ratio of the average tensions on both sides. If it doesn't it means that your tension meter is off. Of course nothing here assures true readings, it just flags a problem.

That said, the meter may still be fine for comparative readings.

zandoval 

Rats FB... Now ya got me. Been trying ta finger this one out but no go... Would Splane it better for me. I am very interested.

FBinNY 

It's almost too simple, so people make it complicated.

Consider that the spoke tension's effect on the rim is a vector with a radial and axial component. Now consider that the total axial forces from both flanges must be equal to each other (add to zero).

Now, we can talk trig, calculating the spoke angles, finding the sines, and doing the math. However, it turns out that everything falls out and all that's left are the 2 CTF distances (net of the be rim offsets), which determine the angles.

It helps to draw a sketch, then start to work out the trig equations. At some point in the process the light will come on and you'll wonder why you didn't know that all along.

zandoval 

I git ya... I too ordered one of those ChiCom tension meters and have been very satisfied with it. But it has taken some getting used to for sure. First of all I don't pay very much attention to the accuracy of the numbers on its dial. I went and measured the tensions on all my good wheel sets with the meter and then calculated the average tension registered on them. Front, DS and NDS. Luckily all my bikes are 700c and 27" running about the same width rim and 14ga spokes. So I got a ball park usable figure for my particular meter. Here is what I came up with, but remember that's for my little ChiCom device that is NOT CALIBRATED.
...........................................................
700c M13II 700c 622
Front: 32-34 Average = 33
Rear Drive Side: 32-33 Average = 31
Rear Nondrive Side: 28-30 Average = 29
...........................................................
Rm19 Weinmann 27-1/4 x 28c / 35c ETRTO 630X19
Front = 31
Rear Drive = 30
Rear Nondrive = 25
..........................................................
CR18 27-1/4 14ga SUNRIMS
Front = 31-32
Rear Drive = 31
Rear Nodrive = 27
..........................................................

Further note: I too had a wheel that had low tension on the NDS after truing. The DS registered normal. I just increased the tension of the NDS and re-trued. Surprisingly I was able to get the tension up on the NDS with very little change on the DS tension...

tFUnK

Looks similar if not identical to the picture posted by zandoval

tFUnK

Thanks. This is on a 24h wheel, but the spokes are pretty thin at 1x2.0mm (edited).

tFUnK

Hence, the reason I posted the question in the thread. Good info overall, and I agree with your points, but the ~0 tension meter reading is what I was most curious about. Like I said, the wheel rides fine, and I have no intention of messing with it.

Going by the relative CTF, though, this wheel is definitely off in that the NDS side is basically 0. I can accept that the tension meter is the problem, and not the wheel itself.

Related question: do people measure tension with the tires mounted and inflated, or without? I feel like that would affect the tension meter readings.

tFUnK

I'm guessing those are the raw readings, not the converted kgf values?

cxwrench

So your rim is not centered now. If you increased NDS tension the rim had to move that way...no way it couldn't have.

FBinNY 

You raise a few points. First of all, as I said earlier, the ratio of total DS to NDS tension is determined (immutably) by the ratio of the hub CTF distances (net of the rim's hole offset). So, if the tensions ratios don't conform, there are two possibilities. Either the rim isn't dished correctly or your meter readings aren't accurate throughout it's range. You can't confirm which withing knowing the other.

As for the low tension, discounting meter error, it might still be right if the spokes are thin, or if you didn't properly factor the gauge when using the conversion chart.

As for when to measure tension (tires or not) you already know the answer. You just don't know that you know, so stop to think a moment. Assuming for the moment, that tires make a meaningful difference, then so would the air pressure. So, do you think that a builder would mount and inflate a tire to check tension before removing it to continue working. If so, how wide a tire, how much pressure, etc.? So, as I said, you know that answer already.

BTW- despite your intentions, you later said you increased NDS tension, so either the wheel was, or now is, not dished correctly.

It's said that poor mechanics blame their tools, but it's my experience that the poorest mechanics overly trust and rely on their tools.

Dan Burkhart 

One issue I have identified with the Park tension meter is that the internal spring is quite strong to the point that it will raise the tension on a spoke by about 6% when measured in my calibration fixture with a reading taken at 100kgf.
Not really a problem when taking readings in the 100 kgf plus range so long as the readings are repeatable.
It is possible that the clones of the Park tool have an even stronger spring which would mean that at some threshold you would get a reading of zero even when there is some tension.
By comparison, my better tension meters only raise the tension by about 1% when taking a reading.

tFUnK

That wasn't me; I merely checked the tensions for fun using my new toy, I didn't adjust anything.

I just re-checked this afternoon and the tension meter values of 2-3 actually translates to ~50 kgf for the spoke type, so not ~0. This was with the tires inflated so I'm guessing that translates to a slightly higher tension if measured without tires. The wheel rides fine so I'll leave it alone. Thanks for your insights.

Lombard

That looks almost identical to the Park tensiometer which is not one I would trust.

Lombard

Measure without a tire. A mounted and pumped up tire will give you erroneously low reading.

zandoval 

Yes... They are the raw readings on a tool that is not calibrated. Its crude but it works for me.

Your post scared me so I just went out and rechecked. The wheel is aligned just right with my Dish less then 1mm difference between DS and NDS. At that time for my uncalibrated tool I was reading 24-25 on the NDS and 29-30 on the DS with the wheel trued. I took the NDS and gave it some tension evenly across all the spokes bringing it up to about 27. I then retrued on the DS and sure enough the DS came up to about 30-31. So really the difference between DS and NDS was about 2 increments on my mystery tension meter. The dish remained dead on.

I am not a wheel builder. But I have replaced spokes and refurbished bent rims. I think nothing of completely loosening up a laced wheel and then bringing it back to life. It a joy to see some people who have a real rythem for wheel truing. I just chug along and kinda play with it till its gets right. Who knows, some day I might even get a wheel truing stand...

FBinNY 

Question for someone with this meter.

Is the conversion chart specific for various gauges?

If so, are they charted by gauge, ie. 14g, or actual spoke diameter, ie. 2mm?

It's important because the spoke diameter factors into the reading, and a thinner spoke will read as lower tension.

tFUnK

Mine came with a sheet of paper, on it were two tables, one for round spokes, another for bladed spokes. Each had columns for different spoke properties (steel, aluminum, titanium, etc., dimensions in mm). The rows showed the kgf corresponding to the raw meter values. The tables didn't have everything (eg, I didn't see 2x3mm bladed spokes, which were on my Ultegra 6600 wheels), but they had a lot on there.

Lombard

They are charted by actual diameter.

Aardwolf

I've been using a Ztto TC-1 cheapo tension meter, as people have said there's no guarantee it's accurate.
One way round that is to calibrate it:One up side of doing this is you can adjust the meter for most sensitivity in the range you're interested in.
Another thing I do is to bounce the meter off the spokes a few times when I'm measuring tension in spoke - the
reading goes down the first couple of bounces. I put that down to friction in the meter.

Here's an earlier thread about calibration: https://www.bikeforums.net/bicycle-m...on-meters.html

sweeks

It would be helpful if you said something about *why* you wouldn't trust this tool.
I've built 6 wheels (not many, to be fair) using the Park TM-1 and they've remained true for thousands of miles. I've found this simple tool to give reproducible readings under my working conditions.

cxwrench

You're not 'truing' the wheel, you're centering the rim.