SUPER BALLOONS.

Press, Volume LXIX, Issue 20789, 24 February 1933, Page 6

SUPER BALLOONS.

TYRE PECULIARITIES. AMERICAN EXPERT'S OPINIONS. The recent introduction of the superballoon type of tyre has been widely discussed by motorists, and the following article furnishes interesting information concerning experiments conducted in the United States: — The American Society of Automotive Engineers recently devoted a whole session to tho subject of tyre peculiarities that engineering skill had to cope with in producing the motor-cars of 1933. Experts traced the progressive steps that have resulted in the production of super-balloons, and gave the results of research by a tyro company and an automobile factory staff. The findings made clear the differences in car reactions to tyro contact with the roadway recurring since the first balloon tyro came into use. Tyre "wander," for example, gives a car tho motion of a fish swimming. Its chief cause is under-inflation of tyres, and low-pressuro tyres generally aro prone to it. A remedy has been found by altering the king pins in the front axle. More reversiblo steering gears have helped, together with increased freedom of steering joints and bearings. Then there is "tramping," which comes from lack, of balance m wheel and tyre assembly. The weight added at one point by the addition of the tyre valve and stem has been known to cause this. Wheel-balanciiig machines have been developed to correct it. Tyre "shimmy" is allied to "tramping," and also may be traced to steering systems. In most cars now the kick-shacklo in the spring suspension eliminates it, or a cross-steering arrangement is resorted to. Mr T. Franzen, a prominent American engineer, said that parking with low-pressure tyres was more difficult than it was with conventional tyre equipment. To meet the new conditions set up by the super-balloons increases had been made in tho steering gear efficiency in preference to increasing sear ratios. This was to avoid unpleasant . high-spoed conditions common to high-gear ratios. , Biding quality, it was pointed out, was'as yet a highly abstract subject, and dependent on many functions' other than those of tyres. Up to date there was no measuring stick available for riding quality, and it was necessary to be satisfied with opinions. .^ The consensus, in Mr Franzen's view, was that the super-balloons, with their lower pressures, gave increased comfort Some of this comfort came from the elimination of high-frequency oscillations, which ordinarily manifest themeelvcs as body noises and rattles. Step by step," he said, "it was found out how to apply the new tyres, so that to-day a tyre life very similar to that of the standard balloon may be antici,Pa AMWcring a question whether , it took more petrol to run a car fitted with low-pressure tyres than with the kin* Mr Franzen citod test findings sWing that tbo differences were insignificant. Iwo cars, identical in every respect, were equipped £ 17 s 5-25 (the balloon size) and 16 x 6 tyres respectively. For a Loss country run of WOO he fuel consumption of the car with t e 1? x 5.25 tyres was 16.1 miles to the ilnnn while that of tho car with the ff °x'6 tyres with 15.6 miles to the humming up the nm of super-balloons Mr Franzen better appoaranco in their favour.,