[GearHead]

I have a Parktool TM-1 spoke tension meter which for some reason went out of calibration. It now reads about 15 kgf too low when I measure the tension on wheels that I know the tension of. I would assume that the spring on the back has suffered from permanent set.

Obviously I want to correct the problem, which is simply done by adjusting the spring preload screw. Does anyone know of anything to use as a baseline for calibarting spoke tension meters? How about comparing it against another calibrated spoke tension meter?

Has this happened to anyone else?

 

[shiggy]

Assuming a 1.8mm spoke 15kgf is ~1.5 marks on the tool's scale. Not that much. How can you be sure the tension in the wheels have not relaxed? It does happen.

The TM-1 instructions clearly state the tool must be returned to them for recalibration if needed.

 

[GearHead]

I checked the tool against some older wheels I have which I haven't rode since I checked the tension on them after first getting the tension meter. I am pretty confident it is reading low.

Whenever I use the tension meter, I am very observant to make sure I hold it in the same center part of the spoke each time, I don't rotate it when taking the reading, I make sure the spoke is sittting right at the bottom of the posts, and I release the handle at the same speed each time. Consecutive measurements on the same spoke are always within 0.25 marks on the tool's scale. 1.5 mark's on the tool's scale is a BIG amount to me.

I read the part about sending it back to Park tools to recalibrate it in the instructions, but I was hoping I wouldn't have to do that.

 

[Blue Shorts]

I'm not saying that you're wrong, especially since the note about recalibration indicates that it can go out of calibration. You didn't mention how long you've had the tension meter or how long ago you checked the tension on the older wheels, so it's tough to figure out what happened, but I figure one of a few things has happened.

1) The tension meter is indeed out of calibration
2) You forgot what the tension originally was on the older wheelset or thought the spokes were a different guage.
3) The tension on the older wheel spokes has relaxed
4) A combination of #1 and #3, above.

The bottom line is that using a wheel to check the calibration of the meter is a bad idea. I think that the spokes on the older wheel would go out of "calibration" faster than the meter. Either send the meter to Park for calibration or find a new meter (or newly calibrated meter) to compare yours with. Your LBS should have a meter that you can compare yours with.

 

[GearHead]

How can you be sure the tension in the wheels have not relaxed? It does happen.

How much do wheels typically relax if the wheels were pre-stressed correctly when built?

 

[Ligero]

When you originally checked the wheel did it have a tire on it and does the wheel have a tire on it now? Having a tire on and aired up will have a effect on the tension readings.

 

[GearHead]

When you originally checked the wheel did it have a tire on it and does the wheel have a tire on it now? Having a tire on and aired up will have a effect on the tension readings.

How much would the air pressure of a tire effect the tension reading? No tire on it both times.

 

[Ligero]

How much would the air pressure of a tire effect the tension reading? No tire on it both times.

Depending on the rim I have seen up to a 10kgf difference with the tire then without.

 

[GearHead]

Depending on the rim I have seen up to a 10kgf difference with the tire then without.

I just checked one of my bikes which has a 1.25" Specialized Fatboy slick on a 26" Sun CR18 MTB rim on it. The difference in spoke tension was 12kgf when I changed the tire pressure from 0 psi to 110 psi. Good to know this.

Thanks,
Trevor