Bicycle wheels need to be straight so rim brakes can be
effectively adjusted and the ride smooth and steady. Crooked
wheels are barely amusing at low speed and create dangerous
wobbles at high. After straightness, however, is the issue of
centering. In order for wheels to easily interchange among
frames and forks the bicycle world has agreed they should be
centered. Centered means the rim and tire are equidistant from
the axle ends. No matter if your wheel is front or rear,
internal gears or disk brake, MTB or road, it's meant to be
centered. The exception is a very bent frame for which,
occasionally, wheels are adapted. No reason to worry about
centering if you have a problem without another solution. Let's
hope that's rare. Wheels are centered as they are built. There
are a number of ways to do this but a dishing tool (wheel
centering is known as "dish") is the overwhelming choice.
Another method is to flip the wheel in a truing stand. The rim
will run the same distance from an indicator, which ever way it