Lltoca,r EorToB Maurice A. Smith D.F.o. 8PorlT! EDtToR Peter Garnier aaattT^tr EDI?ona Leonard A. Ayton, Ronald Barker itlDLAilD.EotroR Edward Eves ART EDt?oe Howard VYse t MAY 1964

ilANAOtNO DIREOTOR H. N. Priaulx m.s.e.

Treading Water ,TtlIE experts $eem to be undccided about the

! importance of tyre tread; when one thioks of I all the different pattem$ to be seen on the roads rhere is sorne excuse for assuming that fashion arrC pertraps the ability to undulate in a convincing manner on the television screen are main considerations. Surely treads cannot all be scientifically designed and yct so differeut?

In accordance with the law of the cussedness of nature, if rou build more grip into a tyre you ate bound to reduce its life, or increase its roll resistancg or irs tcmperature, or its cost. If you give a &iver a ncw tyre that raises the break-away speed on a givco corner he may urcll complain that his car is more dangerous because he is now goiog faster whcn he loses controll The fact reEBiDs that a modern car weighiog up to 2 tons has to find its grip, upor which safe progrets dcperds, throu& four small areas of rubber each "m bigger than the s<rle of a numbq 9 shoe."

One of the more rccent phcrrcmerra with car tyres is callcd aquaplaning. This is primarily 6c result of badly made or maintained rqds whicb allou' large puddles and erreo sheets of water to stand on their surfaces. Speed ard tyre wear are contributory causes and it also arises from t}e use of wider tyres and, it seccrs, frorn ryre tread pattcros which squcegee the watef, instead of ptlrering it up in their cuts (sipcs) and grooves before flinging it out again-

Vhat happeos is that a wedge of water builds up in front of the ryre and at certain speeds and in cenain corditions it may be forced between the ryre tread and thc r@d. Then all gnp is lost for brakirry and stecring, and coatrol becornes nil,

Since there were sorne doubts about tbc occurrencc of aquaplaning, Dunlop carried out convincing tests late last year (Autocu, 3 January 64). Subsequently they have publicized the Glt trcad parrcro, applicable to variqrs covers, which overcomes the rrouble, Of c-ourse, any tyr€ wbich has lost its slots and cus and becomes bald is particularly prone to " floetingr" and &ivecs, espccially those of fast cars, should have this added risk in mind-

During thc rec€at Le Mans practice sctsions, held in bcavy rain (aDd with too few cars passing to.throw lhe water off the roads), several of the cars with low profile tyres (wide, flat ueads) experienced aquaplaning. Two of the new Ford GTs with dry weathcr "doughnut" tyres were arnong those which suffered loss of control.

In more mundane condirions we have recently experienced aquaplaning on the roads-and very disconcerting it can be when the front of the car planes involuntarily suaight on or sideways on a bend. Our erperience followed the fitting of new low-proflle tyres on a staff car. The four * size 9 soles " give superb grip on wet or dry roads until the amount of standing water and the speed (quite modcrate) together cause this aquaplaning. With earlier narower ueads of different pattern this did not occur. A side effect is the way in which water frorn the froot tyres is squished in a quite different way over the front disc brakes ard into the enginc compartrnent of tbe car. This all calls for new aoticipation and extra care on dremhed roads.

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