1. (Units) a unit of heat in the fps system equal to the quantity of heat required to raise the temperature of 1 pound of water by 1Â°F. 1 British thermal unit is equivalent to 1055.06 joules or 251.997 calories.
Quick Answer. A major factor that usually causes tire noise is the air chamber inside the tire. The large void that is filled with air acts as a giant resonance chamber. Thus, the tires are something like donut-shaped drums that generate a low-frequency hum when tires are rolling.
One of the most annoying sources of noise and vibration, and one that is sometimes confused with wheel vibration, is that caused by resonant vibration in the exhaust system. At certain speeds, the natural oscillations that occur in the exhaust may âstack upâ causing the exhaust system to buzz or resonate.