1933-01-01

An Analysis of Tires and Wheels as Causes of “Tramp” 330042

THIS paper presents the solution of the factors in tires and wheels that cause a particular type of front-end vibration termed “tramp,” which is a vertical vibration of the front axle accompanied by a small degree of simultaneous oscillation of the wheel assembly about the king pin. This vibration in turn sets up the disturbance of the body and chassis. The front-axle vibration is caused by the unbalance and variation in rolling radius of the rotating front-wheel assemblies. The theoretical action of these two factors is developed in detail and supported by experimental results.
The foregoing two factors act independently. The resultant of the two periodic forces which they set up depends on their phase relationship. The forces due to unbalance are in the same direction as the forces due to variation in rolling radius and enhance their effect when the center of gravity of the rotating assembly is in the region of minimum rolling radius; they are in the opposite direction and nullify the forces due to variation in rolling radius when the center of gravity is in the region of maximum rolling radius.
The amount of unbalance and variation in rolling radius and the amplitude of the resulting axle vibration necessary to cause tramp varies with different automobiles. They can be reduced by increasing the uniformity of tire-wheel assemblies and their effectiveness can be reduced by proper body design. The problems of the tire, wheel and automotive engineers in eliminating this vibration are discussed.

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