February 7, 2023
Islandix truing tools use the acronym TIR to describe wheel alignment. Originally TIR stood for Total Indicated Runout but over time became Total Indicator Reading. Technically runout is a measure of concentricity, which applies to radial wheel alignment but not lateral alignment (instead a measure of flatness). Wheelbuilders often say runout when referring to both and that’s fine.
Regardless TIR is a Total measure, that is the maximum reading minus the minimum. On a rim brake wheel, for example, lateral TIR is the difference between shortest and longest spans from rim to brake through a full rotation of the wheel. That’s intrinsically useful.
For various reasons some wheelbuilders prefer to describe alignment in plus-minus terms. In this nomenclature alignment is given as the difference between minimum/maximum readings and the midpoint. If you prefer thinking about alignment in plus-minus terms, divide TIR by two.