Always at the forefront in tyre design, the Italian firm of Pirelli released its new tyres to a somewhat startled gathering of motoring journalists in London recently. This tyre, called the BS3, features replaceable treads instead of the conventional one-piece tyre. The manufacturers claim a number of advantages over existing tyres, including the fact that the treads are entirely separate and easily replaceable without special tools; that special ice studs can be fitted to the normal tyre for extra traction on solid ice; that it is possible to replace worn-out treads at a fraction of the cost of a new tyre; that treads can be changed without removing the tyres from the wheel or the wheel from the car, and that these replaceable treads will last as long as complete tyres of normal construction, while the casing can be used with several sets of treads.
The Pirelli Company from Milan was formed in 1872, when one of their activities was the making of bicycle tyres. In 1899 they turned to the manufacture of motor car tyres and throughout the years have remained one of the world’s leading tyre manufacturers. Their contribution to racing has been not inconsiderable since all the World Championships since the war and up to 1957 have been won on Pirelli tyres, but in that year they gave up racing because the speeds of racing cars were becoming too great in the company’s opinion, and the conditions under which they raced were becoming too divorced from everyday motoring for the experience gained on the race track to be of any further use in developing tyres for normal production vehicles. The other reason for their retirement was, of course, that they wanted to concentrate their whole resources on development of new passenger-car tyres — the BS3 being the result.
The BS3 consists of a carcase which has ridges all the way round the outside between which the three steel-reinforced tread bands are fixed. The treads are slightly smaller in diameter than the actual carcase, so they are slipped into position when the tyre is deflated. When the tyre is inflated pressure is exerted all round the casing and the tread bands are virtually immovable.
The basic principle is so simple that it is indeed hard to believe that the tyre will work, but Pirelli have been making tyres too long to make mistakes. Assuming that the tyres are perfectly satisfactory in operation their theoretical advantages are tremendous. The most obvious is that the carcase will outlast two or perhaps three treads, in addition to which one or more of the bands can be removed at any time if damaged or worn unevenly, and instead of changing tyres round every few thousand miles one can merely change the treads. For winter motoring the normal treads can be removed and a set of chunky winter treads fitted in their place, while the others can be stored for replacing in the summer. In the event of a puncture the treads will not detach themselves until considerable deflation has occurred. Even if they do come off the carcase can travel for some distance with no tread at all. In addition, sets of tungsten carbide-tipped spikes are available for fitting in between the treads for use under icy conditions. Tests carried out on an ice rink showed that a car so fitted pulled up in a straight line in a distance of 40 ft. when braked from 25 m.p.h. while a car with conventional tyres spun round and ran into the barrier.
Other claimed advantages are that it is very quiet when cornered hard and that the steering is much lighter than with conventional tyres.
Obviously there will be a great demand for this tyre and Pirelli are gearing up for large-volume production. In Britain the BS3 will be made at the Burton-on-Trent factory, where production will initially be concentrated on the popular 15-in. size.