Abstract: Calibration apparatus (40) for a tire testing machine (11) having an A-shaped framework (13) formed by diverging trunions (25, 26) with a spindle (37) having a face seating a wheel for mounting a test tire (T) movably supported between the trunions including, a pair of beam mounting assemblies (42, 42) affixed in spaced relation on the A-shaped framework, a cross beam (75) supported by the pair of beam mounting assemblies, a calibration bar positioning assembly (85) on the cross beam supporting a calibration bar (120) in spaced relation to the face of the spindle, an angle adjusting platform (95) on the calibration bar positioning assembly for selectively angularly orienting the calibration bar relative to the cross beam, an indicator mounting rod (127) extending from the spindle in a direction paralleling the face of the spindle, a dial indicator (130) extending from the indicator mounting rod for engaging the calibration bar at spaced locations upon rotation of the spindle through approximately 180.degree.