TIRE thump has gained prominence as passenger cars have become quieter and roads smoother. Studies at the CM Proving Ground dating back to 1940 have shown thump to be a very complex example of the simple phenomenon that combining two closely spaced frequency components will produce a certain beat.
Here the authors detail what has been learned about the physical characteristics of car and tire which go into producing thump of various frequencies and loudnesses. They also describe a newly developed portable instrument which measures the depth of modulation of the beat between two frequencies, thus serving as a uniform standard of tire thump severity.
