Front-engine, rear-wheel-drive layout
In automotive design, an FR, or front-engine, rear-wheel-drive layout is one where the engine is located at the front of the vehicle and driven wheels are located at the rear. This was the traditional automobile layout for most of the 20th century. Modern designs commonly use the front-engine, front-wheel-drive layout (FF).
History
The first FR car was an 1895 Panhard model, so this layout was known as the "Système Panhard" in the early years. The layout has the advantage of minimizing mechanical complexity, as it allowed the transmission to be placed in-line with the engine output shaft, spreading weight under the vehicle. In comparison, a vehicle with the engine over the driven wheels eliminates the need for the drive shaft (replacing this with the transaxle of lighter combined weight), but has the disadvantage of concentrating all the weight in one location.
In order to reduce the relative weight of the drive shaft, the transmission was normally split into two parts, the gearbox and the final drive. The gearbox was normally produced with its highest gear being 1:1, which offers some mechanical advantages. The final drive, in the rear axle, would then reduce this to the most appropriate speed for the wheels. As power is the product of torque and angular velocity, spinning the shaft faster for any given power reduces the torque and allows a lighter shaft construction.