Tyre with Separate Treads
Page 62
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ATYRE with tread-ring pieces which may readily be detached and replaced has been produced after seven years' development by Pirelli, Ltd., Derby Road, Burton-on-Trent. It is claimed to represent a radically new conception in tyre construction and to offer an outstanding combination of advantages.
At the moment only pilot production in two sizes for small vehicles is being undertaken, with full-scale production to follow in a few months' time, but giant sizes are in the course of being made.
The BS3 tyre, as it is known, consists of a carcase with two shoulders and two circumferential ribs, leaving three channels. Into these may be fitted tread rings, of which currently two types are being made. One is suitable for normal conditions and the other for use on slippery surfaces.
When the tyre is inflated, the rings are held firmly in position and there is no risk of slipping relative to the carcase either laterally or peripherally.
Removal of a set of rings may be done in just over a minute, even by unskilled operatives, as was found by a representative of The Commercial Motor at a demonstration in London last week. The fitting of a new set of treads as replacements for worn can be done at less cost than would be the case were the carcase remoulded.
It is furthermore practicable to switch a set of treads from the standard to winter pattern with the change of season. If the roads over which a vehicle is to be running are icy, steel spikes may be fitted to the carcase of a BS3 in between the tread rings, gaps being left in the intermediate circumferential ribs for this purpose.
An original set of treads is claimed to last 10 per cent. longer than the tread of a normal tyre. It is also stated by the company that replacement sets should have lives as long as that of the first set, so that not only is there a comparable saving against the cost of remoulds but another in respect of extended life. A carcase will last for the life of three sets of treads.
The BS3 is a tubed tyre, but may be offered in tubeless form in due course. The advantage of a tubeless variant may not, however, be significant as a special valve has been devised for the inner tube. Should a puncture °eau, the escape of air is gradual and the deflation of the tyre compares with what occurs when a tubeless tyre is punctured. Punctures are, in any event, likely to be rare with 8S3 tyres, say Pirelli, because the tread rings are reinforced with steel plies.
The economy of the use of 11S3 tyres cannot yet be computed because the price has not yet been fixed. It is thought likely to be slightly greater than for conventional equipment. The cost of a set of treads, however, is put at a third of the total price of an original carcase, tube and set of treads.
Other advantages of the new Pirelli product are substantially less power absorption and excellent road-holding properties. At 85 m.p.h., the power saving by the use of BS3 tyres on a small vehicle is said to be 16 bl.p. Steering characteristics are appreciably refined. There is a greater degree of accuracy and the amount of effort required to turn the steering wheel is -reduced. On large vehicles, steering servos become less needed than when ordinary tyres are fitted.
A journey of a few miles over wet roads in a sports car equipped with BS3, standard-tread covers demonstrated to The Commercial Motor representative the good road-holding qualities. When break-away of the rear wheels did occur on sharp corners, it was gradual and controllable, and not sudden, and braking could be accomplished without fear of sliding. The quietness of the tyres was also notable—a quality which might appeal to coach operators.