Three defects must be corrected on a bicycle wheel : side to side, up and down and offset.
Once side to side and up and down are fixed, offset must be dealt with. In order to mount wheels on different frames and forks, to ease V-brake adjustment and have a smooth drive, it has become standard practice to center a wheel on frame brackets so in order to have an offset as small as possible. Centered means that the rim is equidistant from the ends of the hubs. Whether your wheel is front or rear, with internal gears, disc, ATV or road, it is supposed to be centered.
This OMT : Offset measurement tools will be available for purchase from September 2019.
To check this centering, you have to measure this offset. With Mach1 wheel assembly machines, you will have no difficulty: All our truing robots have a sensor dedicated to actual offset measurement. Mach1 is the only manufacturer proposing machines whose reading of offset value is true without adding any option. This said, it is also possible to measure this offset manually.
The offset measurement tool is very easy to use. Place it on the wheel and make sure 3 points are in contact with the wheel. Then place the tool opposite by turning the wheel over. If there’s no longer 3 points touching the wheel, there is a defect. But this tool has a kind of magic : it magnifies offset and makes it easier to read. As it is put on both sides of the wheel, the displayed value is twice the actual offset value.
By convention, all Mach 1 machines measure and display offset values in the same way the manual tool does. So if you accept a rim is deflected 0.7mm to the left or to the right of the center of the hub, you will need to set-up a tolerance value of 1.4mm.
Defect value reading being a source of controversy, Mach 1 offers now a tool with a digital readout for immediate and direct offset reading with no room for interpretation.