Calibrating Park Tool TM-1 spoke tension meter

[SimonCelsa]

Hello & Good Day,

any help with the following queries would be highly appreciated.

Having recently fitted a new wheelset to my hybrid cum quasi-tourer I decided to dismantle the old wheelset & attain some practice in the delicate art of wheelbuilding.

I duly downloaded the Roger Musson pro guide to wheelbuilding & constructed a reasonably exact version of his truing stand, albeit using 18mm MDF as opposed to the recommended (but non-existant) 20mm. It is actually a very good bit of kit & comes in at about £25 assuming you have the paint & various other odds n sods lying about in your shed. Actually, printing out the 100+ page guide used almost a whole printer cartridge thus add another £30 I suppose.

Anyhow, I must say the wheelbuilding process so far has been fairly successful I think, no major hitches, the basic 32 spoke, 3 cross pattern. Wheels still round, true & good for a spin. However, for peace of mind I decided to splash the cash on a subject tension monitor ex 'Petra' cycles which was speedily dispatched/received (VG service). Have recently done a bit of 'moonlighting' work & with the wife & kids away it won't hurt the budget too much.

From my limited experience of the subject, & only through casual research, I had a ballpark spoke tension figure of between 90-130 kgf as the 'norm'.

Well, when I checked my proudly assembled wheel I was surprised when the (brand new) tension meter gave relatively uniform tensions of between 155-178 kgf. The rims & hubs are unbranded but reasonable quality, & the spokes are bulk standard 2mm SUS plain gauge. I then checked my new wheelset, Sputniks on Deore hubs (ex SPA so hope they're good!) & obtained similar readings. Same same on my tandem wheels.

Now, the questions are:

a) are these tensions I am obtaining reasonably true, or is the gauge incorrectly calibrated?? It seems an awful lot of force on each spoke & it is right at the high end of the 'tabulated' Park Tool tension range. The spokes feel Ok though when squeezed. I didn't use a 6 foot wrench to tighten the nipples!

b) The instruction sheet says not to tamper with the calibration screw, send it to Park Tools who will do it for you for a reasonable charge. I don't think that's an option with postage etc. So, how to get a reasonable calibration. I have thought of lashing the rim to a beam in the shed, passing a spoke through a rim eyelet & then, utilizing the gap in my front teeth suspend myself from the spoke elbow & then measure the tension. It should read my weight (about 76kg) if I am thinking in the generally correct direction?? OK, there are probably better ways so am open to any inspired ideas.

Anyhow, that's it, thanks for your time.

I will be back at sea for early October for say 3 months so if anyone would like a 'borrow' of the truing jig or tension meter (cost of postage only) for the period Oct-Jan then send me a PM.

Thanks, Simon

[Trigger]

I have thought of lashing the rim to a beam in the shed, passing a spoke through a rim eyelet & then, utilizing the gap in my front teeth suspend myself from the spoke elbow & then measure the tension. It should read my weight (about 76kg) if I am thinking in the generally correct direction??

Make sure you get the wife to video that!

Sorry, I have no idea how to check the calibration of your spoke tensioner. Although most serious engineering places usually have their own calibrating room, so I wonder if it's worth ringing around to see if any of them could help?

[531colin]

Spa wheels are built to the following tensions;
Front; 2.0/1.8/2.0mm double butted spokes...21 on the Park gauge....100kgf
rear driveside; 2.3/2.0mm single butted spokes....25 on the Park gauge.....120kgf
rear nearside; 2.0/1.8/2.0mm double butted spokes...19 on the park gauge....80kgf

They never get tighter with use!

[SimonCelsa]

Thanks for that Colin,

so it would seem that my newly acquired tension meter is not quite calibrated properly.

Still thinking of practical ways to re-calibrate it myself. I Have bathroom scales, 2 spare spokes, a ball of string, pencil & my body weight. Might not be able to sleep tonight with the various permutations.

Cheers, Simon

[531colin]

.............so it would seem that my newly acquired tension meter is not quite calibrated properly...........

They are supplied by Park Tools correctly calibrated from new. You are reading the bit of the table for round steel spokes?

[SimonCelsa]

Yes hello Colin. I'm pretty positive the correct part of the supplied table is being used. The 'steel round spokes' (yellow section on mine).

I'm getting between 27 - 28 deflection on the meter - I know the graduations go upto 48 but the tabulated tensions stop at 28 (on my sheet anyhow).

I suppose the relative tension of each spoke is the most important factor so I will use the SPA front wheel as a 'model' & recalibrate to that - sounds like a resonable idea. As you say, it would be pretty unusual for the spokes to have tightened themselves in the period between obtaining the wheel new, & now.

thanks for your help, Simon

[531colin]

Mines a couple of years old, the different bits of the table aren't picked out in different colours!
I don't understand whats going on, it seems madness to buy a tool to tell you the tension, then to randomly "re-calibrate" it based on a wheel you happen to have knocking about.
The instructions with mine say to expect tensions between 80 and 130 kgf on wheels*, and everything you have checked falls outside those normal limits.
Based on that, I think its reasonable to go back to the shop that supplied the tool and get them to check it against their other gauges, and return it to Park if it seems wrong.

*Thats what I would expect, too.

[SimonCelsa]

I've just ripped out my 2 front teeth whilst suspended from a spoke checking the tenison meter calibration!! Thus I think that a test of 'Petra' cycles return/exchange department is shortly forthcoming. Oh to the joys of internet shopping. Your advise is correct Colin, I think I'll go for an exchange.

Thanks, Simon

[TonyR]

It works by applying a lateral force to the spoke and measuring the deflection across a fixed span. If you want you can do it all with a couple of simple measurements and a calculation

[reohn2]

It works by applying a lateral force to the spoke and measuring the deflection across a fixed span. If you want you can do it all with a couple of simple measurements and a calculation

Spill the beans!

[531colin]

I think this has come up before, and CJ had a way of working out the tension from the (musical) pitch of the spoke....as I recall, he found an on-line tool to generate pure pitched notes! ....of no use to the tone deaf/mathmatically inept among us!

[Mick F]

Spring balance and ruler for the tone deaf but keenly sighted?

Pull and measure should give you some sort of repeatable figure.

[PW]

I still tension my wheels by stress relieving, Brandt style. If it goes out of true in 4 smooth waves back everything off 1/4 turn, re-true and job done. If it doesn't it's not tight enough so give it another 1/4 all round. The tensiometer probably makes the job a lot quicker, which Colin needs if he's working professionally, but I don't sat up in the attic on a wet sunday afternoon!
PS the difference between left and right at the back surely depends on the type of spokes being used? Lazers are thinner in mid span than Sapim race for example, and I'd expect a slight degree of stretch from a Sapim Strong compared to plain gauge.

[531colin]

........................
PS the difference between left and right at the back surely depends on the type of spokes being used? Lazers are thinner in mid span than Sapim race for example, and I'd expect a slight degree of stretch from a Sapim Strong compared to plain gauge.

The difference in tension L. to R. is the same whatever the spokes used....but a thin spoke will give a different reading on Parks gauge than a thick spoke for the same tension...the deflection is influenced by spoke stiffness as well as tension.
(Was it the Red Queen in Alice who said "Anything I say means precisely what I mean it to mean at the time; nothing more, and certainly nothing less" )

[SimonCelsa]

Following on from the original posting:

I contacted the supplier, Petra Cycles of Surrey, and explained that the spoke tension meter appeared to be giving false high readings. An exchange was agreed so I duly packaged the 'faulty' item & return posted.

Today I received...........the same one back again!!!!!! I know it was the same one as I put a little back dot on the spring holder post. It is still giving exactly the same readings as before so basically the instrument has enjoyed a little jaunt through the postal system for a few days.

Either I am using it wrong (doubtful as it quite a simple bit of kit), or my wheels (& the wheels obtained through SPA) are built to the tightest spec possible!!!

What to do? Think I'll just live with it & use it as a 'relative' gauge until such time I garner enough wheelbuilding experience to be able to state confidently & without doubt that it is in fact faulty. Ho Hum.