Is a spoke tensiometer useful for determining that a wheel is on its way to becoming out-of-true?

Question

Question

Is a spoke tensiometer useful for estimating the strength of a wheel and whether it needs preventative truing? One does not need a tool to determine that a wheel that is blatantly out-of-true (either laterally or radially) is out-of-true, but could a wheel be on its way to being out of true, with unequal spoke tension that can be detected with a tensiometer but not by squeezing of spoke pairs?

For example, could a wheel be just subtly out-of-true (say by 0.1 mm) such that a human cannot see the problem, but this out-of-trueness would only get worse with time? (And, a related question: are firmer tolerances one of the factors distinguishing nicer wheelsets from basic ones?)

Context

Of all bike maintenance tasks, wheel truing (and building) seems overwhelming. It consists of adjusting 28-32 independent variables on one wheel. Learning to properly solve the four-dimensional problem of adjusting rear derailleurs is itself nontrivial. One cannot "wing it," but must pursue a method.

But even if I delegate wheel truing and wheel building to a professional, detecting whether and when a wheel requires tension adjustment, if not outright truing, would still be nice to do on my own. Typically I see amateur and professional mechanics alike squeezing pairs of spokes to determine the health or the quality of a wheel. Even pros don't seem to bother pulling out their spoke tensiometers.

Answer 1

There are several diagnostic uses I use a tensiometer for fairly regularly:

One is to get a sense of how good the tension balance and tension level on a wheel is as a way of evaluating if it needs work and how much. This isn't to say that it's usually the first tool reached for. It's not and it often isn't needed at all. But, depending on the situation it can help to gain information. For example, if one encounters a wheel where the tension seems low, the tensiometer allows you to assess further before making the final decision of what you're going to do to it if anything. In this sense, yes a tensiometer is useful in estimating the strength of a wheel, because strength comes primarily from tension. It might be more helpful to think in terms of is it as strong as it could be, as in whether it's tensioned to whatever your target tension is for that rim.

The most common is to help give final, measurable corroboration that a rim has been permanently damaged in cases where it's borderline or not immediately obvious (i.e. no obvious impact areas that become inescapable as soon as you start handling it). In these cases the tensiometer is used in a normal tension-balancing process, and then if and when that process fails to be able to result in a true wheel with reasonably balanced tension (I usually use +/-10% as a generic tolerance, with higher end rims often being capable of better), you have quantifiable evidence that the rim itself is distorted. Note that this is different from throwing the tensiometer onto a wheel as a go/no-go, because until you try to tension-balance the wheel you don't know whether the outlier spots are the result of damage or poor initial tension balance.

A tensiometer is not useful in evaluating whether a wheel needs truing. It's useful in determining whether the state of trueness it has is resultant from good tension or not.

Answer 2

Not really. I imagine a high-end wheelbuilder has a blue wall of expensive park tools because that's what's expected by the high value customer.

If a wheel might be suspect, my quick test is to spin the wheel with a finger lightly touching the side of the rim and leaning on the frame for stability.

A lower-tension spoke will have already resulted in an out-of-true rim - there's no chance to spot a low-tension spoke before the rim goes out of true. If there's enough horizontal runout to be perceptible, you're not doing a preventative truing, it is a rim in need of truing.

A rim-brake wheel needs to be pretty-much spot on, a disk brake wheel can cope with being a little off perfectly flat.

A spoke tension-meter is a nice way for testing, but it is perfectly workable to use the squeeze test to find outlying spokes, or to give the spokes a light tap with a metallic tool to hear a regular ping-ping, ping-ping noise. You should not hear a ^ping or a _twang noise - if you do those spokes need checking as you iterate around the wheel and redistribute the tension in that area.

Wheelbuilding is definitely one of those "hands-on" practical tasks that can be described but are easier to learn by doing. You approach the end goal from all sides at once, rather than finish each task and moving onto the next one. Truing a wheel is just the last few steps of a wheel-build.

Upshot: a spoke tensionmeter would be very far down my priority list for tools for bikes.

Answer 3

Kind of.

The tensiometer allows you to check that the spokes have a high enough tension. If the tension is too low the wheel is going to be weaker and can go out of true more easily.

Inflating your tyres can make spokes relax noticeably, so for road bikes it can kind of make sense to intentionally over-tension the spokes to end up at just the maximum value when inflated.

Answer 4

Wheels that fail have usually two things in common:

• The spoke tension is uneven
• The spoke tension is low

Both are signs of poorly built wheels. In theory, you could have a wheel where:

• The spoke tension is even
• The spoke tension is low

...but you almost never see such wheels, because even spoke tension is a sign of a wheel built by a master wheelbuilder, and those master wheelbuilders tighten the spokes all the way to the recommended tension. (I have had such a wheel once, it was the first wheel I built and I didn't have a tensiometer back then so spoke tension was perfectly even but unfortunately too low.)

You can catch uneven spoke tension by plucking the spokes. If you find a spoke that doesn't ping at all but is completely loose, the wheel is already about at most 100 km away from destruction. If the "ping" sounds is of the same pitch on all spokes, the wheel is good, but if you can hear variation of pitch the wheel is bad.

If you ever find a wheel with low but even spoke tension, you may not be able to diagnose it by plucking the spokes unless you have a reference wheel with identical spoke lengths and thicknesses where the spokes are tightened to the proper tension. But you can immediately diagnose the health of such a wheel by using a tensiometer and finding that the spoke tensions are too low. So yes, tensiometers can diagnose more things than an untrained ear can when plucking the spokes.

Generally the main failure mode of concern is total and complete loss of tensions in all spokes (may happen if tension in sufficiently many spokes is too low), or spokes snapping (happens for poorly built wheels that have not been stress relieved or spoke tensions are uneven or maybe even too low).

The only form of out of trueness that may grow without a total and complete loss of tension in all spokes being a realistic danger is that the spokes have residual twist. That goes away in short time, you hear pinging from the spokes when riding the bike, but if the spokes are sufficiently tight, the out of trueness doesn't grow unbounded but rather results in some residual out of trueness after the residual twist is gone. Most likely you won't even notice it, you just notice the pinging sounds from the spokes. This may annoy you if you run high mechanical advantage rim brakes with very minor pad gap, but may not annoy you if you run disc brakes. However, in 99% of cases if the spokes ping and residual twist goes away, it is a sign that the wheel is poorly built, which means the spoke tensions are most likely both uneven and low, so the wheel is prone to failure in that case too: the failure mode is total and complete loss of tension in all spokes.

Properly built wheels need no truing, ever. You build the wheel once, to high and even spoke tension, and it never needs any adjustment anymore. Learn yourself how to build high quality wheels if you find your wheels need continuous adjusting of spoke tensions. You may start by reading The Bicycle Wheel by Jobst Brandt.