A CAR MANUFACTURER'S EXPERIENCES WITH BALLOON TIRES
In the summer of 1922 the Buick Company began experimenting with balloon tires. The first tires tested, being four-ply and 32 x 6.20 in. in size, produced a galloping action that was sufficient to prejudice the company's engineers against them, and the tests were discontinued. In addition to the galloping effect, other difficulties encountered included those usually present in steering, the development of wheel shimmying to a serious degree, the lack of proper clearance for external brakes because of the small 20-in. wheels, the excessively rapid wear of the tire tread, and the greater susceptibility to puncture. Leaks because of the pinching of the inner tubes also occurred.
When, later, a set of 5.25-in. tires was tried on a smaller car, the galloping was noticeably less; but punctures were more numerous than was the case with high-pressure tires. In another set of 32 x 6.20-in. tires, but of six instead of four plies, galloping was still present, but the durability of the tires was increased. Low resistance to skidding was apparent because of the configuration of the tread, which was of the circumferential-rib variety. It was obvious that defects in the tires must be eliminated before, satisfactory results could be expected.
A decision was reached to adopt sizes of balloon tires that would meet the observed conditions and to make the sizes approximately those of the high-pressure tires previously used. After seven test-cars had been driven a total of 1,500,000 casing-miles, these sizes were made standard.
As an excessive number of punctures in four-ply tires was found to result from the pinching of the inner tubes in ruts, when the roads were frozen, it was decided that the rear wheels, because of the greater load carried and the absorption of driving strains, demanded a heavier casing. Increasing the number of plies from four to five in the 31 x 4.96-in. size of tire practically doubled the mileage performance, as did also increasing the number from four to six in the 32 x 5.77-in. size. A remaining trouble, namely, excessive treadwear on the outer edges of the front-wheel tires, was remedied by raising the air-pressure about 10 per cent.
The conclusions reached are: (a) that large-section balloon tires increase the resistance to steering, particularly at the curb, increase the tendency toward shimmying at the higher speeds, set-up a disagreeable galloping action, and increase the liability to blowouts because of the pinching of the inner tubes by deep hard ruts; (b) making, a compromise by reducing the cross-section of the tire and raising the air-pressure will eliminate the tendency to gallop; (c) four plies are sufficient to protect the front wheels against punctures and blowouts; (d) more than four plies are needed on the rear wheels because of the greater wheel-loads carried and the absorption of driving strains; and (e) from the standpoint of durability, tire pressures should be maintained at the figures recommended.