s””””Arla”””””WVV1.1″,%”^”NAVNArleNArl”NAVVVWeteN”, TYRES FOR RACING AND COMPETITION WORK
By KAYE DON (Don of Avon’s).
T is interesting to recall how a few years ago tyre I failures limited the speeds of some of our famous
racing cars on the track. Many of our readers will remember that a short while ago some of the fastest cars were unable to cover more than, two or three laps at speed without encountering tyre trouble of some description, the most frequent being that of the tread of the tyre leaving the casing. It was not until years when tyre manufacturers were able to produce a tyre which would stand these high speeds that some of our best known motorists were able to drive their at anything like ” all out” speed.
The principal danger of tyre failure at high speed especially on the front wheels where the steering becomes affected, is that the car has a tendency to go right or left, according to which tyre has failed, risk entailed being, of course, apparent when travelling at high speed.
Another danger which exists is that of the tyre the rim and the tube becoming entangled with brake mechanism. Cases have been known where tube has interfered in such a manner as to jamb the brakes and lock the rear wheels, in certain instances with disastrous results. Motor cycle and car racing has been of very considerable assistance to the leading tyre manufacturers in the country. It has been the means of emphasising
defects in tyres in a very short period, the most common of these being the tread leaving the casing, produced by the excessive heat generated by cars travelling at high speeds. This trouble I am pleased to say is practically unheard of to-day, due to the new process adopted by tyre manufacturers in tyre construction.
Tread wear was another thing that manufacturers have been able to improve after exhaustive tests carried out on racing cars. In the past it was no uncommon occurrence to find the tread of a tyre completely worn out after travelling Ioo miles at fairly high speed. Of recent years the writer has seen tyres looking in first-class condition after running in long distance races such as the 200 Miles Race at Brooklands, on some of the fastest cars. It is interesting to recall some of my own experiences on the Wolseley-Viper. Not very long ago I remember using as many as eight tyres in an afternoon in an endeavour to obtain the Mile Record at a speed of approximately 118-120 miles an hour, the trouble then experienced being entirely due to treads leaving the casings. To-day I feel sure it would be possible with any well-known make of tyre to considerably exceed that speed without the slightest difficulty.
Tread Design and Wheel-spin.
With regard to the question of tread design in relation to wheel spin, I feel that for the track undoubtedly the best tread is one with a very slight rib. For road work I should favour a slight ribbed pattern tread for the front wheels and a bolder ribbed tread or a broken bold rib for the rear. For motor cycles the ribbed or lined pattern is much the fastest type for speed events, but for climbing and acceleration a good bold square studded pattern with studs fairly close together is desirable for rear wheels. If the studs are wide apart this will cause a hammering effect and slow the machine, and if inflated bard will result in wheel bounce, which of course means wheel spin and rapid tread wear, also throwing great strain on the beads or wires. If the tyres are used at very low pressure a serious flexing of the walls will be caused and also throw great strain on the beads and slow the machine. The same remarks would apply to car racing. I therefore suggest that a tyre ridden at medium pressure would tend to overcome many of the points raised, as having the tyre inflated to medium pressure it is kept more in contact with the road and the greater speed obtained. The question of when tyres should be scrapped on racing cars is one to which all racing motorists should give close attention. To determine when a tyre is not
fit for further use is somewhat difficult, but the obvious things to look for are to see that the beads are in perfect condition and in no place broken and that the inside of the casing is sound and not breaking up. The question of the tread is, of course, apparent, and providing the canvas is not showing the tyre would be good for further use. Within the last few years vast improvements have taken place in manufacture. It is not many years back that tyre manufacturers were making a canvas tyre. To-day we have a cord tyre which has enabled manufacturers to use very much lighter casing, in fact, I should suggest a casing of four plies would be strong enough to stand very high speeds with ample margin
of safety, as a single ply of good quality cord I inch in width will stand a strain of 420 lbs. With four plies in a casing there is very little likelihood of burst covers. The method of manufacture is that the cords are thoroughly impregnated with specially prepared rubber and each thread isolated from the other with rubber between, which makes the casing more flexible.
It is also interesting to note the trend of tread pattern. A few years back the popular pattern incorporated bold round studs. To-day we find that manufacturers favour the ribbed pattern—usually the outside ribs being broken, forming a pattern of square block and the centre one being continuous.