The nature of the sound produced by running truck tires is primarily due to the tread pattern design. At 50 mph the sound consists of a fundamental in the frequency range 300-400 Hz and of several higher harmonics. Each of these harmonics, including the fundamental, may consist of several separate frequencies; however, the spread of these frequencies is less than one-third octave. The singing, persistent sound produced by certain tire designs is shown to be associated with the level of the higher harmonics, particularly the third and fourth.
