Front-engine, rear-wheel-drive layout

FR 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.^[1] 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.

In an era when gasoline was cheap and cars were heavy, the mechanical advantages of the FR drivetrain layout made up for any disadvantage in weight terms. It remained almost universal among car designs until the 1970s.

After the Arab Oil Embargo of 1973 and the 1979 fuel crises, a majority of American FR vehicles (station wagons, luxury sedans) were phased out for the FF layout - this trend would spawn the SUV/van conversion market. Throughout the 1980s and 1990s, most American companies set as a priority the eventual removal of rear-wheel drive from their mainstream and luxury lineup.^[2] Chrysler went 100% FF by 1990 and GM's American production went entirely FF by 1997 except the Corvette, Firebird and Camaro. Ford's Mustang^[3] has stayed rear-wheel drive, as it must maintain a sporty presence, as were Ford's full-size cars based on the Ford Panther platform (the Ford Crown Victoria, Mercury Grand Marquis, and Lincoln Town Car) until they were discontinued in 2011 in favour of the Ford Taurus, which has a transverse front-wheel-drive layout.^[4]

Some manufacturers, such as Alfa Romeo, Lancia, Porsche (944, 924, 928) and Chevrolet (C5 and C6 Corvettes), retained this layout but moved the gearbox from behind the engine to between the rear wheels, putting more weight over the driven axle. This configuration is often referred to as a transaxle since the transmission and axle are one unit.

In Australia, FR cars remained popular throughout this period, with the Holden Commodore and Ford Falcon having consistently strong sales, though Ford has regularly threatened to replace the Falcon with a front-wheel-drive car. In Europe, front-wheel drive was popularized by small cars like the Mini, Renault 5 and Volkswagen Golf and adopted for all mainstream cars. Upscale marques like Mercedes-Benz, BMW, and Jaguar remained mostly independent of this trend, and retained a lineup mostly or entirely made up of FR cars.^[5] Japanese mainstream marques such as Toyota were almost exclusively FR until the late 1970s and early 1980s. Toyota's first FF vehicle was the Toyota Tercel, with the Corolla & Celica later becoming FF while the Camry being designed as an FF from the beginning. The Supra, and Cressida remained FR. Luxury division Lexus has a mostly FR lineup. The fact that a driveshaft is needed to transfer power to the rear wheels means a large centre tunnel between the rear seats. therefore, cars such as the Mazda RX8 and the Porsche Panamera forego a centre rear seat, and divide both seats by a centre tunnel.

Currently most cars are FF, including all front-engined economy cars, though FR cars are making a return as an alternative to large sport-utility vehicles. In North America, GM returned to production of FR based luxury vehicles with the 2003 Cadillac CTS. As of 2012 all but the SRX and XTS are FR based vehicles. Chevrolet reintroduced the FR based Camaro in 2009, and the Caprice PPV in 2011. Pontiac also had a short run with the FR based G8 and Pontiac Solstice. A Chevrolet Replacement for the G8 called the Chevrolet SS was released in 2013 and uses the FR layout. Chrysler and Dodge reintroduced the 300 and Charger on a FR platform. They also maintain FR layout on the now unibody Durango. Hyundai and Kia have also been working with new FR based vehicles in the US, the Genesis Coupe and Sedan, the Equus and the new Kia Quoris. Ford on the other hand seems to be moving away from FR based vehicles with the discontinuation of the Panther Platform in 2011. Excluding Trucks, Vans and SUVs, the Mustang and Falcon (Australia and New Zealand only (due to be discontinued November 2016)) are the only FR vehicles remaining in their lineup.

Front mid-engine, rear-wheel-drive layout

FMR layout, the engine is located behind the front axle.

In automotive design, a front mid-engine, rear-wheel-drive layout (FMR) is one that places the engine in the front, with the rear wheels of vehicle being driven. In contrast to the front-engine, rear-wheel-drive layout (FR), the engine is pushed back far enough that its center of mass is to the rear of the front axle. This aids in weight distribution and reduces the moment of inertia, improving the vehicle's handling. The mechanical layout of a FMR is substantially the same as a FR car. Some models of the same vehicle can be classified as either FR or FMR depending on the length of the installed engine (e.g. 4-cylinder vs. 6-cylinder) and its centre of mass in relation to the front axle.

Characteristics

• FMR cars are often characterized by a long hood and front wheels that are pushed forward to the corners of the vehicle, close to the front bumper. Grand tourers often have FMR layouts, as a rear engine would not leave much space for the rear seats.
• FMR should also not be confused with a "front midships" location of the engine, referring to the engine being located fully behind the front axle centerline, in which case a car meeting the above FMR center of mass definition could be classified as a FR layout instead.
• FMR layout came standard in most pre–World War II, front-engine / rear-wheel-drive cars.

Gallery

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  All Chevrolet Corvette from the second generation (model year 1963) through current models are FMR layouts as seen in the engine bay of the Chevrolet Corvette ZR-1.

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  The Honda S2000 engine sits clearly behind the top of the shock towers.

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  The peler Morgan +4 and 4/4 are classic "front mid-engine, rear-wheel-drive layouts."

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  The engine bay of the Mercedes-Benz SLR McLaren

References