Spoke Tension


April 07, 2014, 09:59 PM

I recently bought the parktool TM-1 since I wanted to make sure that I was getting the right amount of spoke tension when building wheels.  The readings I'm getting on my current bikes with machine built wheels are quite high - some are even off of the chart for the tm-1 which ranges from 14-25 for the 2.0 mm spokes found on all my wheels.  Relative spoke tensions seem reasonable.  Here are some of the average drive side spoke tensions:

road bike (probably fairly heavy duty single walled rim, 36 spokes) meter reads 25 =>167 kg
Minnesota fatbike, "fat" wheelset (single walled 32 spoke) meter reads 26 => 167+ kg off the chart!
Minnesota fatbike, "29er" wheelset (double walled, likely heavy 32 spoke) meter reads 25.5 => 167+ kg off the chart!
commuter (double walled weinmann XC-260 36 spoke) meter reads 22 => 117 kg - this wheel has had some minor issues with losing tension in spokes and going out of true in the past.

It's my understanding that the rim is almost always the limiting factor when it comes to maximum spoke tension.  Digging around on various forums and checking out manufacturers websites (like here: http://sun-ringle.com/support/ or here http://autobus.cyclingnews.com/tech/fix/?id=tm_1) seems to suggest that these numbers are quite high for everything but my commuting bike. 

The TM-1 has a calibration knob, but it is supposed to be calibrated by Park before it is sold - it's frustrating since I have no way to know if the tensions it's giving are reasonable or not.  The readings are definitely repeatable, but I have no way of knowing if they're even in the right ballpark.

My current wheelbuild is a sun ringle rhyno lite rim for my touring bike. 36h, double walled and eyeletted.  The blanket statement of 110 kg being the maximum spoke tension for all Sun Rims seems quite low to me especially based on the readings I'm getting from my other wheels.

So I guess I have two questions:

What would the ideal drive side spoke tension be for my current bikes and the build I'm working on?
Is it likely that the readings I'm getting are actually correct?

Any help would be greatly appreciated!

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« Last Edit: April 07, 2014, 11:18 PM by mccarthy »

XXX

April 08, 2014, 08:08 PM

Your readings don't seem too outrageous, but I am neither a professional mechanic nor an engineer. If you check out the Park Spoke Tension Calculator, it gives different Kgf values for the readings you are stating TM-1 chart: http://www.parktool.com/tm-1-tension-calculator

I generally aim for a reading near 25 on a drive-side 2.0mm spoke (120Kgf), but if you haven't noticed any stress cracks on your other wheels, I might not change them. On my card, a 22 on a 2.0 spoke reads 86 Kgf, which in my experience is too loose.

Lastly, if you are worried about calibration you are free to borrow my TM-1 for comparison.

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XXX

April 08, 2014, 10:52 PM

Thanks Matt!

Turns out I'm an idiot and misread my chart - the numbers I thought were for the 2.0mm spoke are actually for the 2.3mm spoke.  So yeah, as you said, the values I'm getting now are completely reasonable. 

Cleared up my worries about my fatbike wheelsets having too high of tension.  I think I'll follow your suggestion and go for a 25 (120kg-f) on my current build.  I'll probably bring the tension up a bit on my commuter to see if that will help keep it from going out of true as well. 

Thanks again for pointing out my silly mistake!  I also appreciate you offering to compare with your TM-1, but now that I'm actually reading the gauge correctly, I'm confident that the readings are reasonably accurate especially given all my trouble free wheelsets are in the 120 kg-f range which seems like a good target based on both your recommendation and others that I've seen.

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