TYRES OF THE FUTURE

Hawera Star, Volume LII, 19 November 1932, Page 12

TYRES OF THE FUTURE

SIZE AN IMPORTANT FACTOR, BIG BALLOONS MUST PROVE THEIR WORTH. It is difficult to foretell what sized pneumatic tyres will be used • a few years hence. The sizes now standard throughout the world were the rational outcome of the wide swing from highpressure tyres to medium balloons, some eight or nine years ago. At that period it was predicted that super-sized balloon tyres, ranging from 7-J- to 9 inches in diameter were likely to become standard equipment. A few such tyres were made, but neither the motor industry nor the public was ready for such outsized tyres. The outcome was a- general increase of about Jo per cent, in section "sizes of the tyres then standard, by all leading makers. Even that increase necessitated appreciable alteration, in car. design, ..notably in steering and adoption of shock absorbers.

During the last two- years, owing to tlm increased sbeed capabilities of cars and the demand for the utmost in comfort-, there has-been a trend toward increasing tyre section sizes, and al-rc-adv manv cars and trucks in New Zealand are running on tyres considerably larger than were used on similar vehicles a few years back.

Car and tyre manufacturers are no: satisfied that the ultimate has yet been reached in respect to low-pressure, large-sectioned- tyres, and the latent developments indicate a tendency tc swing back to the abnormal-sized balloon tyres, which makers experimented with back in 1923. Already replacement business in a small way is being done with these outsized balloon tyres, which are inflated at pressures varying from 10 ‘to 201 b a square inch, according to size and load. These large sectioned tyres do not c-all for largei wheels, the increase in section being tn,ken care of by the use of -very small rims, which range from 12in to I6in diameters, so that the disc wheels in appearance look mostly tyre. Three - sizes of these super low-, pressure tyres are being made by Dunlop (England), viz., 6.50 in for IGin rims, 7.5()in foi loin rims, and O.OOin for 13in rims for those motorists win are prepared to make certain sacrifices for extra comfort, particularly over pot-holed and wavy roads, loose sand etc. The use of such tyres will probably call for further modifications in design of the cars to be fittecl, to en sure steering clearance and satisfactory tyre service. The outcome of tests conducted with a six-cylinder sedan cai fitted with 9.5GiiV tyres on 12in rims, after necessary -alterations had been made to steering layout, mudguard widths and clearances, will interest motorists.

It is premature to forecast what will be evolved from the latest developments, but the new form of big-balloon tyre has yet to prove itself, a better all-round tyre proposition than those now standard before the world’s leading motor manufacturers and tyremakers will face the colossal outlay incidental to a radical change in wheel and tyre equipment. It has been computed that a sum exceeding £0.000,000 would be alone involved in the" making of the new tyre moulds, etc. It is certain there can bo no startling change in this direction, and- any development will be gradual. On bad. surfaced roads there was really 'useful improvement- in riding comfort —on main highways little advantage. A badly pot-holed road was taken at 15 to 20 miles an hour faster than on standard tyres. The steering was appreciably heavier, the drag being intensified at low speeds and when manoeuvring. Maximum speed was reduced three to four miles an hour. On most hills there was a definite reduction in climbing power, necessitating more use of gears. Hill-climbing speed was reduced about 10 per c-ent. During acceleration from 20 to 30 miles an hour in top gear it took tw< to throe seconds longer. Petrol_ consumption was increased about 15 per cent., which conceivably might to n degree be offset by decreased body and chassis maintenance. As regards braking on most surfaces it was good, on wet bitumen the stopping distance was slightly increased, while the liability to skid on greasy surfaces was greatly minimised. So far results have shown that the mileages obtained art less than with the standard tyres.