A British thermal unit (Btu) is a standard unit of energy that is used in the United States and sometimes in the U.K.
There is another defect in tires that can cause a vibration called loaded road force variance. The tires and pass a visual inspection, a radial and lateral runout test, be perfectly balanced, but still cause a vibration. This is due to the internal defects in the tire.
Other Noise Sources. Not all tire noise is due to the design of the tread pattern. Tires also make noise because the tread elements squirm under the weight of the car and slip over the pavement. At low speeds, some of the easiest places to observe this type of noise are parking garages with polished concrete floors.