Final Drive Ratio: The ratio between the transmission output shaft r.p.m. and the drive-wheel axle shaft r.p.m. It is determined by the ring and pinion gear inside the differential. For example, if the ratio is 4.00:1, the driveshaft rotates four times for each rotation of the rear axle differential gear, the axle shafts and the wheels. A car's acceleration and fuel economy can be altered by the final drive ratio. A low numerical axle ratio (example: 3.07) is known as a fast ratio, because road speed is relatively fast for any given engine speed. The characteristics of this ratio are: lower engine speed, reduction in performance ability and lower engine revolution per mile so fuel economy is improved. A high numerical axle ratio (example: 3.73) is known as a slow ratio, because the road speed is relatively slower as compared to the engine speed. The effects are: raised engine speed, increased performance ability, increased engine revolutions per mile and increased fuel consumption.