it has to do with where the tire is placed relative to the rim. There is a colored dot placed on most high performance tires that indicates the position of the 1st harmonic of the tire and it is determined by the tire manufacturer by road force balance. The rim has (or should have) a colored dot near the edge (my Z has a white dot) that marks the rim average low point determined by the factory or by measurement as the rim ages from use. The factory dot on the tire should be mounted to match the low point dot on the rim. That is match mounting to have the least error for good road feel after balance remember you can dynamically balance a cube on a shaft). Most retail shops do not know match mounting from pairs sex. They usually place the tire dot at the valve stem pure BS unless the tire has a second mark on it that indicates placement at the valve stem as a second option if the rim low point is not marked.
If your rim has no low point dot it is easy enough to locate it by simple measurement. Just ask if you want to know the procedure as most shops will not do it unless a performance tire shop and you ask for the service.
