The Perfect Bicycle Wheel
The perfect bicycle wheel will display five qualities at the same time.
First, the wheel will be radially round to within 0.5mm tolerance. That is, when you spin it, you will not notice large variances in the diameter of the wheel, and you should not notice any marked hops as the wheel spins.
Second, the wheel will be laterally true to within 0.5mm tolerance. That is, when spun, the wheel will exhibit no side-to-side wobbles.
Third, the wheel should be dished correctly so that the rim is centered over the hub, meaning that when installed in the bike, the wheel will be centered in the frame.
Fourth, the tension should be high enough to maintain the stability of the wheel. Most wheels are under-tensioned. Properly tensioned wheels are more efficient, stay truer, and experience less spoke breakage. The highest tension possible is a function of the type of material used in the hub and rim, but modern components made from quality materials can usually withstand very high tension.
Fifth and last, the tension must be balanced out on the spokes such that, on any given side of a wheel, all of the spokes are very close to the average tension for that side. This is very important. It is also time-consuming and tedious, but it makes a big difference in the wheel's performance.
A final comment on the perfect wheel is that you cannot tell it by looking at it. People love to take a wheel, spin it, and knowingly watch the wheel while it spins and observe whether it looks true. I certainly hope that any builder of a bicycle wheel can turn out something that has no side-to-side wobble. Looking at a wheel tells you nothing except the obvious. Assessing the less obvious (but more important) characteristics of dish, tension magnitude, and tension consistency require persistent measurement with calibrated instruments. A meticulous builder of bicycle wheels may make over 100 spoke tension measurements during each wheel build.