At The Wheel

NZ Truth, Issue 1202, 13 December 1928, Page 22

At The Wheel

CENTRE OF GRAVITY Considered to Be Responsible For Wheel Wobble and Shimmy ENGLISH ENGINEER'S VIEWS Lecturing before the Society of Arts, W. Beaumont, aax English engineer, devoted considerable attention to the centre of gravity of modern motors, holding that low centre of gravity introduced a number of defects m design and smoothness of run- . ning.

DEAUMONT pointed out, amongst D other results of the low centre of gravity, that it made a cranked front axle necessary, and that this was, he thought, the cause of wheel wobble and shimmy. In this connection he said: "Every obstruction/ and every variation m road- resistance met with by the road wheel on the , ground is- transmitted through the crank arm of the axle to the attachment of the spring with a turning movement proportional to the crank arm dip of the axle. "Rotative motion iof the crank arm is resisted by the attachment of the spring. "The spring has to resist the turning effort, not only by contrary elastic fixture of the front anU rear half of the spring, but by transverse bend; or twist-resisting effort, the axle crank being exposed to twisting stress and" a rearward bending stress. "The wheel on its axle, with its axle, is thus angularly and momentarily dis-

placed from its visrht-Uned advance, only to be brought back to it by the elastic effort of the spring. "The repetition of this action, and the spring recoil, give to the wheel that evidence of vibrating spring effort, which results m what is called wobble, or shimmy. "It will thus be seen that the greater the crank dip or difference between the height of the spring clipped part of the axle, and that of the axle on which the wheel runs, and the greater the distance from spring clip to wheel centre, the greater the stresses on the crank axle and on the springs," he went on. "A long cantilever from spring clip to king pin is bad. "The wheel shimmy is thus^the accompaniment of modern ear design. It was never remarkable m cars of a dozen years ago, and it has not been extinguished m any degree by the palliatives which have recently been tried, or suggested.'.' .