These are generally cross-ply, a high-load casing of nylon construction with a wide, flat, nondirectional tread giving full tractive effort in both forward and reverse directions on all types of surfaces. Invariably the undertread is considerably thicker than normal.
To dispel a myth about ply rating; it no longer means the number of plies or cords used to construct the carcass of a tyre. The operative word is 'rating.' The strength of the casing is equivalent to the number of plies of cotton which were used to construct original pneumatic tyres. Therefore, in theory, a single cord, if it is strong enough, can be used and providing its tensile strength is equivalent to 12 plies of cotton, the tyres will be 12-ply rating.
Pneumatic tyres are generally of low initial cost, but when subjected to abuse, they are most likely to fail. On forklift trucks the problem areas are the tread, shoulder and sidewalls. A puncture or blow-out invariably occurs when the machine is being used or at the most inconvenient time. Add to this the drivers' time, loss of production, mechanics' time, repair equipment and in some cases demurrage, and the cost of a puncture then escalates considerably from the cost of a patch.
In all pneumatic tyres it is not the tyre which carries the load, but the air pressure. Under or over inflation can have detrimental effects in exactly the same way as normal road tyres. Over inflation suggesting an excess load or faulty inflation equipment creates an abnormally high crown resulting in extreme wear down the centre. Under-inflation can be even more damaging, particularly on the extra heavy-duty industrial tyres.
Failure invariably occurs on the sidewalls as a blister where the rubber separates from the casing. As the load is being carried by the air pressure in the tyre, under-inflation can be extremely dangerous as vehicle stability is affected. In one case, a long load on a high lift slipped on the forks when a tyre burst, resulting in the machine turning over. In a second case, in a paper factory, a 5 ton reel of paper was dislodged from the clamp and crashed through a brick wall when a tyre burst.
Although pneumatic tyres have disadvantages in industry. there are advantages which cannot be denied, superior traction, flotation and maximum shock absorption.
If the application is suitable for a pneumatic tyre, the buyer should select an industrial tyre, looking for:
One manufacturer produces three types of industrial pneumatics, these being standard, wire and XPT. The industrial pneumatic with wire has the normal heavy-duty casing overlapped by two full plies of twisted high tensile steel wire, each 3.2 mm thick - 6.4 mm in all from bead to bead not just the tread area. The XPT (Extra Protected Tread) is a two-compound tyre to assist cooling. The whole tyre is of extra-heavy construction. In certain applications, specifically designed single tyres, such as 12.1 x 15 20 ply, can be used which previously have required the dual configuration of 8.25 x 15.
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