MistaMuShu

I've never seen either, but shouldn't they be the same thing? What is different about the two? What is printed on that chart that comes with a tensiometer?

I get the feeling that the tensiometers not intended for bicycles won't work for bikes:

https://en.wikipedia.org/wiki/Tensiometer

Could someone explain how bicycle tensiometers work? It doesn't sound like it'd be all that complicated to build (I could be severly mistaken)

mechBgon

I sometimes used a Cricket automotive belt tensiometer. It's not an ultra-precision instrument but it has some advantages of its own. That's one experimental tool purchase I didn't regret.

MistaMuShu

How does the tool work? I'd guess you'd clip two ends onto a spoke and there'd be a spring in the middle to measure the tension? The ones I see on ebay all have LCD fancy-schmancy readouts and still cost less than the bikes ones...

mechBgon

Simply lay it against the spoke, or fan belt, or guitar string or whatever, and push 'til it clicks, then look at the reading. It's not material-dependent or dimension-dependent, either, so no need to have a calibration chart for titanium versus stainless, different gauges, oval, flat bladed, etc. About the only thing to remember is to push the spoke in a neutral direction (fore/aft).

Having built quite a few Zipp wheels with bladed Ti spokes in my time (and NEVER lost a nipple inside a Zipp rim either! /gloating), it was nice to have a way to gauge overall tension level without resorting to dark arts with a conventional tensiometer. I know people are all over the map on every conceivable aspect of wheelbuilding, so some may be scandalized at the idea that a $10 Cricket is worthy of touching their high-zoot wheels (mercy, it has no dial gauge?! ) but whatever.

I left my camera at work or I'd post a pic of ye olde Cricket in action. Maybe Monday

AGuinness

I bought a Wheelsmith Tensiometer recently. The thing is specially designed so that a section of the spoke will snuggle into a little notch in each of its ears. The previous poster was correct in that there's a spring in the middle, as you can see. On the bottom edge of each plate is a scale, they look something like this:


...TOP PLATE:.....|100..|90...|80...|70...|60...|50...|40...|30...|20...|10...|

BOTTOM PLATE:.....|.....|.....|.....|.....|.....|.....|.....|.....|.....|.....|


Once you've got the tool on the spoke you want to measure, you look at the scale and find the two lines that most closely line up. If the line is at 60, that's the reading. If two lines fall between 60 and 70, it's 65. Then you take a look at your calibration chart, and according to the thickness of the spoke (at center), it will give you the tension in kilograms—it lists round spoke thicknesses of 2.0, 1.8, 1.7, 1.6, 1.55, & 1.5 and aero spoke thicknesses of 1.4 x 2.6, 1.1 x 3.2, 1.2 x 2.2, & 0.9 x 3.1.

Apparently, each tensiometer is calibrated individually and so you can only use the chart that came w/ it. Another one won't give you an accurate reading. Both the tensiometer and the chart have a specific serial #.

As to building one at home, well... I guess you could give it a shot.



S.

AGuinness

Oh, the more heavy-duty Hozan tensiometer has a dial.

I'd like to see that cricket, as I spent over a hundred bucks on mine.

Still nice to have the Wheelsmith® Tensiometer though—it came in a nice little cardboard box, and is quite pretty.

mechBgon

I have a Wheelsmith as well I do use it for round steel spokes in cases where the spoke dimensions are actually on the chart. Mine's probably 13-14 years old and has fewer dimensions on its chart, though

MistaMuShu

It just sounds like the cricket is better because it doesn't care what dimensions or materials it uses. I'll definitely watch for this pics :-)

waterrockets 

I have the Park TM-1. It gives you a number, usually in the 17-25 range. You look on a chart for the spoke diameter and get the tension in kgf. It cost me $50 IIRC, and it works just fine. It's very consistent and easy to use. I start by choosing my target tension, looking in the table to figure out what reading I want (like 21.5 or so is common for my 2.0/1.8/2.0 spokes). Then I only need to look at the reading for each spoke.

mechBgon

Here's a pic of the Krikit, which I misspelled by spelling it properly It's currently indicating about 105kg force. To use it, you lay it against the ______ and push down on the concave black part until it clicks, then look at the black "needle" to see where on the tension scale it's flush with the surface. Tada!

Rincewind8

Keep in mind, that the material makes a difference. The usual bicycle spoke tensiometer measures resistance to bending and not the tension directly. Different spokes (thickness and material, even shape) have different bending resistance even without being tensioned. That's why the bicycle spoke tensiometers are calibrated and come with a chart with different spoke types and diameters. Only that chart tells you the true tension.
Automotive belts on the other hand usually have very little bending resistance when untensioned.
If you know the material characteristics of the spokes you can calculate the tension in the spoke from the deflection in a specified side loading with a known force. The charts that come with those tension meters basically spare you the "know the material characteristics" and the calcualtion part.

MistaMuShu

But even without knowing the "true tension" from a chart based on materials and spoke diameter, isn't it enough to use the krikit to measure relative tension between the different spokes; That is to say, to make sure that all of the spokes are tensioned within a certain range?

Do rims and spokes have a defined range they should be tensioned to?

mechBgon

Some people get caught up in trying to get all the spoke tensions just so, measuring each spoke's tension and OMG they are not equal, must... try... harder!

If that works for you, great Personally, I don't. During a wheel build, I check the same single spoke as a gauge of general spoke tension, but use musical tone to work on getting spoke tension as even as practical, while at the same time progressing towards increasing roundness and trueness. It gets excellent results for me, and it accounts for the reality of rims that aren't inherently perfect and require imperfectly-balanced spoke tension to get the optimal results.

As I mentioned, wheelbuilding is home to a vast range of techniques and philosophies, so that's just my 2¢

MistaMuShu

I hear you on this point. And from the responses other people have given, it sounds like a tensiometer is meant to double-check spokes to be similar tensioned in a ballpark range (~5% deviance). The tuning fork approach has the added benefit of entertaining musical accompaniment while you work.

$70 is still too much to pay for a spring with a dial and a look up chart... But then again, there are more unreasonable purchases to be justified.

AGuinness

In Gerd Schraner's The Art of Wheelbuilding, are the following ranges:

(Front; Rear Right; Rear Left.)

.F:.....900 - 1,000 N
........200 - 225 LBS

RR:.....1,000 - 1,100 N
........225 - 250 LBS.

RL:.....600 - 700 N
........135 - 160 LBS.

I translated these to kg's:

.F:.....90 - 101.25

RR:.....101.25 - 112.5

RL:.....60.75 - 72

These figures are based on "the most popular standard hollow section rims (MAVIC 317, 571, 321, 521, Open Pro)..." Later he mentions that: "On rims with high V-Cross sections (CAMPAGNOLO Atlanta, RIGIDA DP 18 and 22), and when using hexagonal nipple heads, spoke tension can be as high as 1,500 Newtons (340 lbs.)."

There's more in the book on this, which I can't all transcribe—but I recommend it for those interested in wheelbuilding. I also recommend this site I recently found: Spoke Length Formula with Wheel Lacing and Building Information.

S.