A portable machine for testing on site the uniformity of a tire or other components of a tire/wheel assembly. A compact rigid frame has a base formed by a plurality of longitudinal and transverse frame members for supporting the machine on a planar surface. A box-like subframe is mounted on the base and supports a mounting plate for the tire/wheel assembly. The mounting plate is slidably mounted on a pair of slide rods extending upwardly from the subframe. A road wheel and drive motor are mounted on the base, with the motor being mounted within the subframe and the load wheel being located beneath the tire/wheel assembly mounting plate. An air spring raises and lowers the mounting plate for placement and removal of a tire/wheel assembly thereon. A loading mechanism applies a force on the tire/wheel assembly mounting plate to forceably move a tire into contact with the road wheel, and is measurable by a first load cell. A second load cell is mounted on a spindle of the tire/wheel assembly mounting plate and measures forces exerted on the tire along five separate axes. A probe located adjacent a tire being tested transmits signals to an electronic processing unit which generates a graphic display of the tire's uniformity.