875 Wheel and tyre runout

Before proceeding to balance the wheel asseembly the wheel should be checked for run-out in both lateral and radial directions relative to the axis of rotation. If the wheel or tyre run-out is excessive it should be corrected before the wheel assembly is balanced.

Lateral run-out (Fig. 8.56) If the wheel being examined has been jacked clear of the ground and when spun appears to wobble so that the wheel rim or tyre wall moves axially inward or outward in a wavy fashion lateral (sideway), run-out is taking place. This may be caused by either the wheel rim being buckled or the tyre being fitted unevenly around the rim of the wheel so that the wheel assembly will produce dynamic imbalance. Deflating the tyre and repositioning the bead against the inside of the wheel rim will usually correct any tyre lateral run-out. Lateral run-out of the wheel itself should be no greater than 2.0 mm.

Radial run-out (Fig. 8.57) If with the wheel jacked clear of the ground, the wheel and tyre assembly appears to lift and fall every time the wheel completes one revolution, then the distance from the axis of rotation to the tyre tread instead of being constant around the periphery of the tyre is varying.

Mean axle height

Fig. 8.57 Illustration of radial tyre run-out

This error is usually caused by the tyre having been fitted eccentrically about the wheel rim so that when the wheel assembly is spun, radial run-out will be observed, and as a result, the wheel assem bly will be in a state of static imbalance. Tyre eccentricity can usually be cured by repositioning the tyre on the wheel rim. The maximum wheel eccentricity should not exceed 2.0 mm.

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