CAUSES AND RECTIFICATION OF UNEVEN TYRE WEAR
The causes of uneven tyre wear are often difficult to diagnose individually; it is advisable, in such cases, to check all the following points: —
(a) Tyre pressures (see "General Data Section").
(b) Brake freedom and balance, brake pad and shoe settings, disc and drum condition (see Section K).
(c) Front wheel alignment (see Section F).
(d) Front wheel camber angles (see Section F).
(e) Play in hub bearings. Adjustment is described in Section F under the heading "Front Hub Adjust-ment".
(f) Play in steering joints. See Sections F and J for the renewal procedure.
(g) Wheel lift and wobble. On a truly mounted and revolving wheel the difference between the high and low points measured at any location on either tyre seat (Fig. 2 at "A") should not exceed 0.050 in. (1.0 mm). The lateral variation measured on the vertical inside face of the flange (Fig. 2 at "B") should not exceed 0.050 in. (1.0 mm). The positions "C" and "D" may be used when the tyre is mounted on the rim.
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(h) Balance of the wheel and tyre assemblies. The tyres should be checked for both static and dynamic balance (see under ‘Tyre and Wheel Balance").
(I) Condition of road springs and shock absorbers (see Section F and H).
Irregular wear may be caused in addition by the local road conditions, such as from a combination of steep camber, abrasive surfaces and frequent hills and bends. Driving methods may also be involved; thus with all the above points properly checked, uneven wear~ may still be experienced. The only solution in such cases is to regu-larly reposition the wheels and tyres as described under "Maintenance".
WEAR CHARACTERISTICS
Certain faults which cause uneven tyre wear produce easily recognisabie wear characteristics. With knowledge of these characteristics, the fault may often be quickly diagnosed and the rectification procedure considerably reduced.
Incorrect tyre pressure
Tyre distortion due to persistent under-Inflation causes rapid wear on the shoulders and leaves the centre stand-ing proud. Over-inflation has the opposite effect, i.e., excessive wear on the centre tread leaving the shoulders standing proud.
Misalignment of the front wheels
The tyre tread having been scrubbed off laterally is caused by wheel misalignment. An upstanding sharp fin on the edge of each pattern rib is a sure sign of mis-alignment.
With minor misalignment, probably aggravated by road camber, the ribs may have sharp edges instead of up-standing fins.
Excessive wheel camber
Excessive wheel camber causes rapid and one side tread wear. Road camber can have the same effect. When a check of the mechanical factors reveals nothing abnormal, interchange the front wheels diagonally with the rear wheels, see under "Repositioning tyres".
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