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Shimmying was noticeable before four-wheel brakes began to be used, but since that time the trouble has been greatly increased. Two kinds are distinguishable; (a) low-speed shimmying, a violent wabble of the front wheels about the king-pins without a bouncing of the front axle, and (b) high-speed shimmying, a severe bouncing of the front axle during which one hub is up while the other is down. This occurs at somewhat higher tire-pressures and at high car-speed. Believing that both forms are not correctible by changing the design of the tire and are only slightly affected by changes in the steering-gear, efforts were directed toward prevention rather than correction.

Shimmying, although known for many years, did not become a serious problem until the arrival of the balloon tire and the four-wheel brake. Apparently, shimmying is of two kinds: the low-speed variety, which is merely a persistent front-wheel wabble without an abnormal bouncing of the axle, and the high-speed species, which is chiefly a persistent bouncing of the axle accompanied by wabbling of the wheels. The two most obvious effects are wheel wabble and axle bounce. As low air-pressure seemed to be the cause, the attention of the tire makers was first devoted to stiffening the body of the tire in various ways, but the results obtained were not satisfactory; and the conclusion was reached that the solution lay in making the car control the tire rather than attempting to control the car through the design of the tire. These considerations led to a search for mechanical means of control.