As part of my project to do my own bike maintenance, I thought I'd take a shot at wheel truing. I had just gotten through rebuilding the suspension on my recumbent bike and I wanted to make sure my wheels were as straight as possible.
Truing a wheel is deceptively simple. There is only one adjustment possible: you simply tighten or losen the spoke nipple. How hard could that be? Doing a little research I realized that there is quite a bit to the subject. First of all, unlike traditional bolts on a bike, you don't adjust spokes to a specific torque setting. Although a spoke is really a very long, thin bolt, you adjust spokes by turning the nipple (nut) to adjust the tension.
Furthermore, there are four different parameters that you are adjusting during the truing process. These parameters are lateral true (side-to-side movement), radial true (in-out movement), dish (the offset of the rim relative to the center of the hub), and spoke tension.
Balancing all of these parameters at the same time is what makes truing a wheel a challenge. However, with the right tools and a little bit of patience, it is a rewarding process.
The right tools
While it is totally possible to true a wheel right on your bike, it isn't always that convenient. I figured if I was going to give this project a go I might as well buy a good set of tools. I selected a quality truing stand, truing stand base, and spoke tension meter. I decided not to buy a dish tool (more on that in a minute).
You don't really need a truing stand base (listed above) as you can easily mount the truing stand in a vise (if you have one). However, having the base means the stand becomes portable and easy to use indoors (a nice feature).
As far as spoke wrenches go, if you have the Park Tool AK-37 Tool Kit, it already comes with three common spoke wrench sizes. However, I also have a bike with "aero" wheels. These wheels might need a special wrench to adjust the spoke nipples (like Park tools' SW-15 listed above).
Adjusting the stand
Park tool has a bunch of helpful articles on their web site. In particular, I found an article covering the adjustment (centering) of their truing stand. If you have the stand properly centered (mine was off by a couple of mm), the you don't need a tool to "dish" your wheel. The calipers on the truing stand will tell you if your wheel is properly dished.
Here is a closeup of a wheel in the stand showing how the calipers let you see the dish as well as adjust the wheel.
The two arrows show the side-to-side gap (lateral true) as well as the in-out gap (radial true or run out). Since this is a front wheel (with no dish), it should be precisely centered between the calipers (as you can see above).
Of course if your wheel should be dished, it would have a larger gap on one side or the other. If you like, when adjusting for dish, you can flip the wheel to work with the other side. All of this depends on the stand being properly centered. Once you check/adjust the centering of the stand, you shouldn't have to do it again (or very often).
Measuring your spokes
Before truing your wheel you should know how to use the spoke tension meter to measure the spoke tension. Spoke tension is usually determined by the rim manufacturer. For example, I was truing a Mavic MA-40 rim. Unfortunately, I couldn't find the recommended tension so I just used a generally recommended tension of 100 kgf (Kilogram Force).
In order to use the tensionmeter, you need to determine what type of spoke you have (steel, aluminum, carbon, bladed or round). Then you need to measure the diameter of the spoke (as shown here):
In this case, I have round, steel spokes with a 1.7mm diameter. Then you use the tension meter to measure the spoke tension:
Finally, you lookup the value from the tension meter using the conversion chart:
For example, a reading of "20" for 1.7mm round steel spokes means a tension of 98 kgf.
So, what does all this mean? Well, people typically recommend that spokes (on each side) have the same relative tension (+/- 20%). This means the spokes should have a tension range of 80 to 120 kgf (or have a reading of 18 to 22 on the meter). When you have spokes outside of this range you risk damaging the rim, breaking spokes, or having your wheel go out of true quickly.
Also keep in mind that if you wheel is dished, the average tension of your spokes will not be the same on the left side as the right side.
Adjusting the spokes
To tighten or losen the spokes you need a wrench that exactly fits the spoke nipple. Don't use the wrong size wrench or you might strip the nipple. Also keep in mind that the spokes use standard right-hand threads. However your point of view while truing the wheel means that you turn the spoke nipple in the opposite direction that you would normally think. In the image below, the arrow points in the direction of tightening the nipple and tensioning the spoke.
If you have aero wheels in which you can't access the spoke nipple from the underside, you'll have to remove the tire and adjust the spokes from the outside. The holes for the nipple will likely have very little clearance, so you need a thin walled socket to make the adjustments
Adjusting these spokes works the same way, but is a bit more intuitive since the direction you turn the nipple isn't backwards.
An iterative process
As mentioned before, adjusting all four properties of a wheel (tension, dish, lateral true, radial true) is a bit of a balancing act. Every adjustment you make to a spoke affects the entire wheel (to some degree). Getting everything right while keeping the spokes in the right tension range is what makes the process a challenge.
However with the right tools, reading a bit about the process, and a lot of patience, you can master it. Wheel truing is a really facinating subject and there are some great resources on the web, here are a few that I recommend.