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.
Just because you can't feel a lot of free play or wobble in a wheel doesn't mean there isn't enough to cause vibration. It doesn't take a lot to be responsible for objectionable vibration at speeds of 60 to 70 mph and aboveany deviation from a truly circular spin is called runout.