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.
Wheel Balance: Out-of-balancetires will cause a car to vibrate at certain speeds, usually between 50 and 70 mph. A tireis out of balance when one section of the tire is heavier than the others. One ounce ofimbalance on a front tire is enough to cause a noticeable vibration in the steering wheel at about 60mph. To balance a wheel, the technician will mount it on a balancing machine which spinsthe wheel to locate the heavier part.