How to True a Wobbly Wheel
Over the years, I have observed many children's bikes with dangerously loose spokes, have helped adult cyclists with loose or broken spokes, and have learned via the internet that problems with broken spokes and even rims are common. Although I can say nothing about the quality of brands of spokes and rims, I do know how to tighten spokes properly, which will save rims and spokes and perhaps even bones from getting broken.
In spite of false beliefs to the contrary, fixing a wobbly wheel is an easy process, requires a simple and inexpensive tool, and normally takes very little time. Truing a wheel usually will be easier than replacing a chain.
In an emergency, it is even possible to use a small crescent wrench to true a wheel, but I would highly recommend against that practice, as rounding the nipples even slightly will ruin them. On the cheapest bikes, the spokes can not be tightened because they are made of too soft of material.
The one tool that you need to true a wheel is called a spoke wrench, which tightens the spoke by twisting the nipple. Don't go into a bike shop and buy one without thinking, because spoke wrenches come in various sizes. Fortunately, for those who are uncertain about the size or who have multiple wheels, multiple-sized spoke wrenches are sold. These aren't as comfortable to use as the single-sized wrench; however, and there is also a danger of accidentally using the wrong size and thus rounding the nipple (which means it must be replaced).
Bike shops and catalogs also sell truing stands and dishing tools. However, the bicycle itself, if turned upside down, makes a perfectly adequate truing stand and dishing tool, even for rebuilding wheels. Truing stands and dishing tools are ideal for wheel-builders but are unnecessary for occasional truing and wheel-building.
Let's start by first looking at the wheel itself, as an understanding here will lead to more satisfactory results. Note that I am not explaining how to build a wheel, a more complicated process which I have done quite a few times.
The modern tangential spoked wheel was an invention of James Starley, who -- along with his son Matthew and his nephew John -- was largely responsible for the modern bike. Originally, wheels were radial spoked, that is the spokes ran straight from the rim to the nearest part of the hub, but Starley discovered that tangential spokes (the spokes run at an angle to a part of the hub which faces another part of the rim) were much stronger, especially for the driving wheel. If you look at a wheel, you will see that the spokes on each side cross other spokes (they are usually laced together rather than just crossing; that is, each spoke goes over one spoke and under the next). Most wheels are three cross (3X), although rear touring wheels are often 4X, and some tandem wheels are 5X. When wheels are crossed and laced, the spokes help strengthen each other, rather than standing alone. In addition, when you are braking and accelerating, the tangential spokes help distribute the load better. Nonetheless, the spokes that most often break are the eight or nine (out of 64 or 72) that directly transmit the driving force from the rear wheel.
Each spoke has a head on one end and screw threads on the other. The spoke heads alternate facing in and out on the hubs, with the holes they fit countersunk for the bends in the spokes (not for the heads!). Likewise, on the rim, the holes are usually slightly off-center. On the front wheel (and some rear wheels), the spokes are the same length on both sides, but on most derailleur bikes, the spokes on the freewheel side are shorter and tighter to help center the wheel on the axle (they would otherwise be off-centered due to the space taken by the freewheel). A broken spoke must be replaced with one of the same length which must travel through the hub and spokes following the same pattern as its seven or eight identical fellows.
On the rim end is the nipple, which although much less visible, is just as important as the spoke, as I discovered one time when a spoke broke off inside the nipple, and I had a spare spoke but not a spare nipple. Quality nipples can stand more tightening without rounding than cheap ones. Of course, to see all of the nipple, it is necessary to remove the tire, tube, and rim tape. The nipple has a notch for a screw driver inside the rim which is helpful when replacing a spoke, but it also has a four-sided face on the outside, for your spoke wrench, where most of the adjustment will take place. It is usually not necessary to remove the tire to just tighten spokes.
If we had a perfect wheel to work with, every nipple would be turned the same number of turns, and every spoke would be just as tight as its fellows. When making a wheel by hand, every effort is made to approximate this situation, although some slight differences are going to occur due to slight variations in the materials. However, most wheels are made by machines which only approximate the perfect wheel. With a machine-made wheel, some spokes are a little too tight and others a little too loose, and as time goes on the difference grows, leading to a wobbling wheel.
All that would be necessary to correct a perfect wheel once it became wobbly would be to find the loose spokes responsible and tighten them sufficiently. It would never be necessary to loosen any of the tightest spokes, as there is no force acting on the bicycle wheel that can tighten them. However, on the machine-made wheel, some spokes may have been too tight to begin with and may have been the cause of other spokes becoming loose. Therefore, while most attention should be paid to the loose spokes, some attention must be paid to the very tightest spokes. Indeed, these very tight spokes are the first (or the next) that are going to break.
Generally, I ignore the spokes and concentrate on their effect on the wheel. However, at the very beginning, it is worthwhile to see if some spokes are extremely tight or extremely loose. I mark any very tight or very loose spokes with different colored tape, say black for too tight and red for too loose. If a wheel is badly out of whack, I might go ahead and approximately match these to their fellows; however, if the wheel needs only small adjustments, adjusting them now can make the whole job more difficult.
I would highly advise to start with the worst problems first. After you take the worst wobble out of the wheel, then the wheel is prepared for fine adjustments and, by that time, you will feel more comfortable about making them.
There are two kinds of adjustment that need to be made to the wheel through tightening the spokes. One is for roundness, the other for straightness. when truing for roundness, two spokes next to each other pull in the same direction, but when truing for straightness, two adjacent spokes pull in the opposite direction.
If you must make both kinds of adjustments, true for roundness first. However, as the roundness is less important than side-to-side motion (because the tire itself is only approximately round), if you are not making major changes, truing for straightness is all that is required. Sometimes the wheel may need major adjustments, but you are on a bike trip and just need to get home (or to the next stop first), but more often the wheel is basically OK but a wobble needs to disappear or a spoke needs to be tightened.
To correct a wheel for roundness, it is best to remove the tire and tube, to make it easier to observe the rise and fall of the rim. The wheel is put back on the bike without the tire, the wheel is spun, and a pencil, flat piece of metal, small board, or whatever you wish to use is placed below the wheel against the fork, very close to the wheel, so that even very slight variations of roundness can be observed. If you position your object just right, the wheel will strike it only at the most out-of-round position. Take your truing wrench and tighten the spokes where the rim hits, never tightening any spoke more than half a turn until you have also tightened its fellows and then tested for the result. Be careful to not tighten the spokes on one side more than the other, as this increases the wobble.
To true for straightness, it is generally not necessary to remove the tire (if the spokes were longer than necessary, removing the tire and filling the spokes may be required to avoid flats). Turn the bike upside down and spin the wheel, and apply the brake very slowly until the wheel starts to hit against the brake. (NOTE: I am assuming here that the brake is centered properly and doesn't pull against one side more than the other. If the brake does not work properly, use a pencil, piece of wood, or whatever, and move it gradually against the spinning wheel to see where the wheel will stop. You might want to use something, such as a felt-tipped pen, which will mark the rim. Be very careful when not using the brakes that you don't overcorrect.) When you find that the wheel is hitting on one side at one point, you know that the opposite spoke needs to be tighter at that point. In the event that the rubbing is pronounced, you may need to tighten more other-side spokes, perhaps the ones on either side of the rubbing point (but not as much as the one in the middle) or perhaps two spokes or four spokes. This is an art, not a science, so it's OK to experiment; however, keep all changes minimal until you perceive what you are doing. I would suggest turning the nipple wrench no more than half a turn on any spoke at any time. I would also suggest marking the spokes you have tightened, perhaps with a little clear tape.
After the wheel runs true; that is, it does not hit against either brake pad even when the gap on either side is only about 1/8 of an inch, go back and check on the extra tight and extra loose spokes that you started with. If they are now like their fellows, the wheel is done. If there are still loose spokes and tight spokes, then the loose spokes need to be tighten and the process repeated. I don't pay as much attention to looseness and tightness as I do to the rim because comparing tightness is difficult to do, while aligning the rim is fairly easy.
Why have I said nothing about loosening spokes that are too tight? If the wheel was made very well, it won't be necessary to loosen any spokes. Think a second: is it possible for the spoke to gradually get tighter as the wheel is used? No. Then we should only have to worry about loose spokes, unless one or more spokes were too tight when the wheel was originally made. There's a common cause of one spoke being too tight that must be mentioned. Assume we have spokes A, B, and C on the same side of the wheel. If A and C become loose and B does not, B will continue to hold the wheel straight until it breaks or you loosen it. So, it is a better philosophy to assume the wheel was made correctly and not to loosen any spokes unless it is unavoidable. Even then, it should be only one or two spokes that are too tight; otherwise, the rest are all too loose.
This probably all sounds more complicated than it is. To demonstrate that it is not all that difficult, I can point out that I completely rebuilt one wheel on the road. On my 1990 touring trip, I discovered I had overtrued my rear wheel (all the spokes were too tight). When I reached the Land Between the Lakes, I spent the morning at my camping site in removing the tire, completely loosening all the spokes, and rebuilding the wheel on the spot. The wheel has never given me any trouble since. When merely adjusting the side-to-side wobble of a wheel, fifteen minutes to half an hour is ample time, and you won't even get your hands dirty, if careful.