[Note: this is #5 in a series of 20 tips to be published during 2009.]
Most riders know their wheels by brand, color, and trueness. If that's as deep as your insight goes, you'll have a tough time becoming a wheel guru. The special feature of bicycle wheels is the wire spoke structure and the tension forces that inhabit it. Invisible to the eye, these forces give the wheel its remarkable strength and, when unbalanced, are responsible for most wheel issues.
While most builders accept the importance of tension, they do little to check it. Without monitoring tension a wheel's most important asset remains invisible. Building and repairing wheels is a matter of deducing the situation and making the right corrections. Imagine trying to diagnose an illness with no more to go by than the most superficial symptom. You might resort to chanting and incense. Some of the wheel work I've seen consists of little more than superstition. Understandable, since tension (the soul of the wheel) remains invisible to many.
In order to effectively evaluate a wheel you need to see its tension. To measure every spoke is slow, awkward, and often inaccurate. What to do? The answer is simple, communicate with the wheel directly. I suggest two ways:
Laying On of Hands
I don't mean blessing your wheel but, instead, discovering a wheel's tension through your hands. Whenever a wheel needs evaluation, grab parallel sets of spokes (as in Tip #4) and give them a very gentle squeeze, just enough to feel the approximate tension and the balance left to right. Swiftly move around the wheel with these gentle squeezes. The first time you do this, you'll discover very little unless you chance upon a broken spoke. In that case, congratulations. You've discovered a major flaw before attempting any sort of repair. Otherwise, however, the feelings in your hands are not going to mean much.
Trust me, the more you do this squeeze, a sort of wheel quick interview, the more it will mean. With experience, you'll instantly know much about the wheel that won't need translation from numbers. For example:
(1) What gauge of spoke (heavy or light)?
(2) What approximate tension level (loose, snug, tight, or hyper-wound up)?
(3) How is the basic tension balance (uneven tension can't hide from your hands)?
(4) Are there any major problems (broken or bent spokes, totally loosened spoke, etc.)?
After your "interview" all this data will wordlessly enter your brain and guide your next actions. You'll save huge amounts of time that otherwise might be wasted with tentative, spot truing that's often not constructive to the wheel. For example, a single loosened spoke will generate a broad "S" bend in the rim, a sort of sine wave. If you try and correct this by truing each section of the wave, rather than discovering the true culprit, you'll have wasted time and possibly worsened the wheel's condition. Eventually, of course, you'll find the culprit. Your measure as a builder is how quickly you can find the source of a wheel's trouble and make a bulls eye correction.
Lay your hands on the wheel, trust that you will begin communicating. This is something to which blind people are better accustomed. Many of them can handle an object or gently feel a face and form an accurate mental picture. Practice makes this a highly effective means to identify and evaluate. If the blind can read through their finger tips, you can read wheels through your hands. The difference between those that can form quick and accurate mental maps of wheel tension and those who can't is huge. It's like night and day. I pity builders who are essentially blind in their work, stumbling around, superstitious, expecting weird outcomes and struggles. Don't be among them.
Hear the Music
A second great trick is learning a wheel's tension by plucking spokes. The most important aspect of wheel tension is uniformity. Uneven spoke tension is more of a liability than an incorrect average. Average tension counts but much less.
Each time you find a suspicious area in a wheel, usually a visual untrueness, pluck the nearby spokes, looking initially for something out of the norm. You'll often find it: sometimes a spoke is significantly looser or, the classic, a same-side pair in which one is tighter the same amount as its neighbor is looser. That latter case is easy to fix: simply loosen the tighter one and tighten the looser. 90% of the time, trueness is unaffected, the rim was responding to the average. Like a suspension bridge with a few loose cables, such a structure might look straight but is actually less supported and stable than if the tensions were even.
In an enlightened wheel workshop, there's plenty of plucking, sounding a bit like a harp tuning studio. Tension is easy to detect. You just have to pluck.
By mastering these two techniques to see the otherwise invisible tension of wheels, you're becoming a wheel whisperer. Your friends and customers will begin to appreciate the wordless communication you have with their wheels. Eventually, you'll deduce and fix wheels in a fraction of the time it takes others. The bottom line is: wheels are cheerful, evolved structures that are happy to share their tension secrets with those who take the time to look.