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.
As a rule, most hubs with sealed wheel bearing assemblies should have less than .002 inches of runout. More than that may cause a vibration and/or tell you the bearing is failing. A sawtooth or heel-and-toe wear pattern on the tires can also produce vibrations and noise that may be speed sensitive.