Car manufacturers often build vehicles with certain distinctive features, such as design style, engine type, target markets, etc.. Such characteristics are basically what distinguishes each from the other automaker.
Eventually each manufacturer and their philosophy evolve, adapting to markets and emerging trends along with the technology.
With this prologue, begins this article about the Automobile layouts most used, some traditionally used by certain manufacturers, others implemented due to the need to evolve in a competitive market.
In automotive design, the automobile layout describes where on the vehicle the engine and drive wheels are found. Many different combinations of engine location and driven wheels are found in practice, and the location of each is dependent on the application the vehicle will be used for. Factors influencing the design choice include cost, complexity, reliability, packaging (location and size of the passenger compartment and boot), weight distribution and the vehicle’s intended handling characteristics.Layouts can roughly be divided into two categories: front- or rear-wheel drive. Four-wheel-drive vehicles may take on the characteristics of either, depending on how power is distributed to the wheels.
Front-Wheel Drive (FWD):
Front-wheel drive (FWD) is a form of engine/transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel-drive vehicles feature a transverse engine, rather than the conventional longitudinal engine arrangement generally found in rear-wheel-drive and four-wheel-drive vehicles.
FF means “Front engine, Front-Wheel Drive”.
This type of layout has suffered important changes through time;
Early cars using the FF layout include the 1929 Cord L-29, 1931 DKW F1, the 1948 Citroën 2CV, 1949 Saab 92 and the 1959 Mini. In the 1980s, the traction and packaging advantages of this layout caused many compact and mid-sized vehicles to adopt it.
There are four different arrangements for this basic layout, depending on the location of the engine, which is the heaviest component of the drivetrain.
Mid-engine / Front-wheel drive
The earliest such arrangement was not technically FF, but rather mid-engine, front-wheel-drive layout (MF). The engine was mounted longitudinally (fore-and-aft, or north-south) behind the wheels, with the transmission ahead of the engine and differential at the very front of the car. With the engine so far back, the weight distribution of such cars as the Cord L-29 was not ideal; the driven wheels did not carry a large enough proportion of weight for good traction and handling. The 1934 Citroën Traction Avant solved the weight distribution issue by placing the transmission at the front of the car with the differential between it and the engine. Combined with the car’s low slung unibody design, this resulted in handling which was remarkable for the era. Citroën and Renault used this layout in some models into the 1980s.
The Renault 5 was one of the last successful mid-engine, front-wheel-drive layouts.
Front-engine longitudinally mounted / Front-wheel drive
The 1946 Panhard Dyna X, designed by Jean-Albert Grégoire, had the engine longitudinally in front of the front wheels, with the transmission behind the engine and the differential at the rear of the assembly. This arrangement, used by Panhard until 1967, potentially had a weight distribution problem analogous to that of the Cord L29 mentioned above. However, the Panhard’s engine was very light, reducing the effect. The engine of the Citroën 2CV was in front of the front wheels, with the transmission behind the axle and the differential between the two. This became quite popular; cars using this layout included the German Ford Taunus 12M and the Lancia Flavia and Fulvia. This is the standard configuration of Audi and Subaru front wheel drive vehicles. The first generation Oldsmobile Toronado and the Saab 99 and “classic” Saab 900 had their engines mounted approximately on the front axle center line, with power being taken by chains or a gear train to a transmission and differential mounted below and beside the engine.
Front-engine transversely mounted / Front-wheel drive
Issigonis‘s Mini of 1959 and related cars such as the Maxi, Austin 1100/1300 and Allegro had the engine transversely mounted. The transmission was located in the sump below the crankshaft, with power transmitted by transfer gears. The 1955 Suzuki Suzulight also introduced a front engine with a transversely installed engine in a city car/kei car application.
Dante Giacosa‘s Autobianchi Primula of 1964, Fiat 128 and Fiat 127, put the transmission on one side of the transversely mounted engine, and doubled back the drivetrain to put the differential just behind the transmission, but offset to one side. Hence the driveshafts to the wheels are longer on one side than the other. This located the weight just a bit in front of the wheels. It is this system which dominates worldwide at present.
Vehicles with the Giacosa arrangement tend to suffer from torque steer under heavy acceleration. The shorter drive shaft, being stiffer than the longer drive shaft, transmits the motion to the wheels immediately instead of ‘winding’ up due to the drive torque. The net result is more tractive force at the wheel with the shorter drive shaft and the car tends to pull to the opposite side.
Rear-engine, Front-Wheel Drive:
A rear-engine, front-wheel-drive layout is one in which the engine is behind the rear wheels, but drives the front wheels via a driveshaft, like a conventional front-engine, rear-wheel-drive vehicle traveling in reverse.
There is some interest in developing the idea for use in cars of the future, as evidenced by the patent application of inventor–engineer Michael Basnett at Rover Group (GB), who proposes a front transaxle design, rear flat engine architecture.
Rear-Wheel Drive (RWD):
Rear-wheel drive (RWD) typically places the engine in the front of the vehicle and the driven wheels are located at the rear, a configuration known as front-engine, rear-wheel drive layout (FR layout). The front mid-engine, rear mid-engine and rear engine layouts are also used. This was the traditional automobile layout for most of the 20th century. Nearly all motorcycles and bicycles use rear-wheel drive, either by driveshaft, chain, or belt, since the front wheel is turned for steering, and it would be very difficult and cumbersome to “bend” the drive mechanism around the turn of the front wheel. A relatively rare exception is with the ‘moving bottom bracket’ type of recumbent bicycle, where the entire drivetrain, including pedals and chain, pivot with the steering front wheel.
Front-engine, Rear-Wheel Drive (FR):
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 typically use the front-engine, front-wheel-drive layout (FF).
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. Chrysler went 100% FF by 1990 and GM‘s American production went entirely FF by 1997 except theCorvette and Camaro. Ford’s Mustang 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.
1986 Ford Mustang
Front Mid engine, Rear Wheel Drive (FMR):
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 (FR) layout, the engine is pushed back far enough that itscenter 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.
- 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.
Rear mid-engine, rear-wheel-drive (RMR)
This kind of layout is also known as MR (Mid-engine, Rear-Wheel drive).
In automobile design, an MR or mid-engine, Rear wheel drive layout is one in which the rear wheels are driven by an engine placed just in front of them, behind the passenger compartment. In contrast to the rear-engined RR layout, the center of gravity of the engine is in front of the rear axle. This layout is typically chosen for its low polar inertia and relatively favorable weight distribution (the heaviest component is near the center of the car, making the main component of its moment of inertia relatively low). The layout does suffer from a tendency toward being heavier in the rear than the front, which is not ideal for handling. However, it is generally felt that the lower polar inertia more than makes up for this. The mid-engined layout also uses up central space, making it impractical for any but two-seater sports cars.
In modern racing cars, MR is the usual configuration and is usually synonymous with “rear engine”. Due to its favorable weight dynamics, this layout is heavily employed in Formula racing cars (such as F1s).
This configuration was also common in very small engined 1950s microcars, in which the engines didn’t take up much space.(…)
Its space-inefficiency means that it is mainly used in sports cars, for example the Porsche Boxster and Cayman, Toyota MR2, Pontiac Fiero, Honda NSX, Lotus Elise, MGF, and supercars such as the Pagani Zonda, recent Porsche Carreras, Ferrari Enzo, Lamborghinis, McLaren F1, Ford GT, etc. See the List of MR Cars for a complete list. The Zündapp Janusis perhaps unique, in that it is literally mid-engined and nearly symmetrical with passengers on both ends of the engine.
Rear-engine, Rear-Wheel Drive (RR)
In automotive design, a RR, or Rear-engine, Rear-wheel-drive layout places both the engine and drive wheels at the rear of the vehicle. In contrast to the RMR layout, the center of mass of the engine is between the rear axle and the rear bumper.
The disadvantage to a rear weight bias is that the car can become unstable and tend to oversteer when decelerating (whether braking or lifting off the throttle). In turns, this tendency is much more pronounced, to the point that even letting off the throttle slightly while turning can cause the rear tires to suddenly lose grip, and the vehicle to slide rear-first (see lift-off oversteer). When this happens, rotational inertia dictates that the added weight away from the axis of rotation (generally the steering wheels) will be more likely to maintain the spin, especially under braking. This is an inherent instability in the design, making it easier to induce and more difficult to recover from a slide than in a less rear-weight-biased vehicle. All cars regardless of drivetrain layout obey the same laws of physics and can do this, but it is much easier to do and harder to correct in MR and RR vehicles, with the result that many are unsafe to drive to their limits by average drivers (notable examples include the early Porsche 911, earlier years of the Toyota MR2, and the Chevrolet Corvair). A skilled driver, however, can corner faster by taking advantage of this tendency to oversteer, and is also more likely to take turns at a correct speed by braking before turning, and maintaining slight acceleration through the turn. At the end of the turn, the rear weight bias allows for increased rear traction when accelerating, allowing the driver to accelerate sooner, a major advantage in racing.
Due to the handling difficulty, the need for more space efficiency, and the near ubiquitous use of liquid-cooled engines in modern cars, most manufacturers have abandoned the RR layout. The major exception is Porsche, who have developed the 911 for over 40 years and have taken advantage of the benefits of RR while mitigating its drawbacks to acceptable levels, lately with the help of electronic aids.
All-Wheel Drive (AWD), Four-Wheel Drive, 4WD, 4×4:
Note: in North America, Australia and New Zealand the term “four-wheel drive” usually refers only to drivetrains which are primarily two-wheel drive with a part-time four-wheel-drive capability, as typically found in pickup trucks and other off-road vehicles, while the term “all-wheel drive” is used to refer to full time four-wheel-drive systems found in performance cars and smaller car-based SUVs. This section uses the term four-wheel drive to refer to both.Main article: Four-wheel drive
Most 4WD layouts are front-engined and are derivatives of earlier front-engined, two-wheel-drive designs. They fall into two major categories:
- Front-engine, rear-wheel drive derived 4WD systems, standard in most sport utility vehicles and in passenger cars, (usually referred to “front engine, rear-wheel drive/four-wheel drive”), forerunners of today’s models include the Jensen FF, AMC Eagle and Mercedes-Benz W124 with the 4Matic system and Suzuki Grand Vitara with/without 4 mode transfer case.
- Transverse and longitudinal engined 4WD systems derived almost exclusively from front-engined, front-drive layouts, fitted to luxury, sporting and heavy duty segments, for example the transverse-engined Mitsubishi 3000GT VR-4 and Toyota RAV4 and the longitudinal-engined Audi Quattro and most of the Subaru line.
For a full explanation of 4WD engineering considerations, see the main article on four-wheel drive
In terms of handling, traction and performance, 4WD systems generally have most of the advantages of both front-wheel drive and rear-wheel drive. Some unique benefits are:
- Traction is nearly doubled compared to a two-wheel-drive layout. Given sufficient power, this results in unparalleled acceleration and driveability on surfaces with less than ideal grip, and superior engine braking on loose surfaces. The development of 4WD systems for high performance cars was stimulated primarily by rallying.
- Handling characteristics in normal conditions can be configured to emulate FWD or RWD, or some mixture, even to switch between these behaviours according to circumstance. However, at the limit of grip, a well balanced 4WD configuration will not degenerate into either understeer or oversteer, but instead break traction of all 4 wheels at the same time into a four-wheel drift. Combined with modern electronic driving aids, this flexibility allows production car engineers a wide range of freedom in selecting handling characteristics that will allow a 4WD car to be driven more safely at higher speeds by inexpert motorists than 2WD designs.
- 4WD systems require more machinery and complex transmission components, and so increase the manufacturing cost of the vehicle and complexity of maintenance procedures and repairs compared to 2WD designs
- 4WD systems increase power-train mass, rotational inertia and power transmission losses, resulting in a reduction in performance in ideal dry conditions and increased fuel consumption compared to 2WD designs
- The handbrake cannot be used to induce over-steer for maneuvering purposes, as the drivetrain couples the front and rear axles together. To overcome this limitation, some custom prepared stage rally cars have a special mechanism added to the transmission to disconnect the rear drive if the handbrake is applied while the car is moving.
Unusual 4WD layouts
- From 1989 onwards, some models of Porsche 911 feature a rear-engined 4WD layout, which is akin to a longitudinal front-engine 4WD layout installed backwards with the engine at the rear of the car
- From 2007 onwards, the Nissan GT-R features a front-engine 4WD longitudinal layout, but with the gearbox at the rear of the vehicle. This provides a more ideal weight balance, and improves directional stability at very high speeds by increasing the vehicle’s moment of inertia around the vertical axis. This layout necessitates a second prop-shaft to carry power to the front wheels.
- Some types of farm tractors and construction site machinery use a 4WD layout where the wheels on each side are coupled together, rather than the wheels on each axle, allowing these vehicles to pivot about their center point. Such vehicles are controlled in a fashion similar to a military tank.
- The Citroën Sahara had a 4WD system using complete Citroën 2CV drivetrains at both ends of the car, such that the engine at the front powered the front wheels and the engine at the back powered the rear wheels.
- A ‘through the road’ hybrid vehicle uses a conventional piston engine to power two wheels, with electric motor/generators on the other two wheels, giving a form of part-time 4WD.
- The 2005 Jeep Hurricane concept had an all-wheel drive layout that featured two V8 engines powering a single driveshaft, with a gearbox mounted in the center of the vehicle. The gears connected to two additional driveshafts, one on each side of the vehicle, that delivered power to the wheels via driveshaft joints. This was designed in order to accommodate the vehicle’s unique steering system.
Rear-engine, Four wheel drive (R4):
Notable vehicles with the R4 layout include several high-performance Porsche sports cars, including the 959, the 911 Turbo since the introduction of the turbocharged version of the 993 series in 1995, and the 911 Carrera 4 introduced with the 964 series in 1989.
Some Volkswagen Kübelwagen (the rear-engined beetle-based military vehicle used by Germany in World War II) variants were produced with 4-wheel or all-wheel drive, including the Type 86, Type 87, Type 98.
Front-engine, Four wheel drive (F4 layout):
In automotive design, an F4, or Front-engine, Four-wheel-drive layout places the internal combustion engine at the front of the vehicle and drives all four roadwheels. This layout is typically chosen for better control on many surfaces, and is an important part of rally racing as well as off-road driving.
Most four-wheel-drive layouts are front-engined and are derivatives of earlier front-engined, two-wheel-drive designs.
This layout is also the drive train of choice for off-road pickup trucks and SUVs. It allows these vehicles to get the most traction without sacrificing precious cargo or passenger room. The center differential is often not present in these vehicles, meaning the 4WD system does not allow any difference in front and rear axle speeds. For normal road driving, these vehicles are shifted into 2WD mode, preventing damage to the transfer case; though full-time systems cannot go to 2WD mode.
The engine could be longitudinally/transversely-mounted:
Mid-engine, four wheel drive (M4 layout)
It is a type of car powertrain layout. Although the term “mid-engine” can mean the engine is placed anywhere in the car such that the centre of gravity of the engine lies between the front and rear axles, it is usually used for sports cars and racing cars where the engine is behind the passenger compartment. The motive output is then sent down a shaft to a differential in the centre of the car, which in the case of an M4 layout, distributes power to both front and rear axles.
The centre differential contained within many 4 wheel drive cars is similar to the conventional differential in a 2 wheel drive car. It allows torque to be distributed to both drive axles whilst allowing them to spin at different speeds, which vastly improves the cornering of a 4 wheel drive car on surfaces with high grip such as tarmac. However, unlike the differentials on the drive axles which are configured to provide torque equally to both wheels, the centre differential is usually set to have a bias to one set of drive wheels or the other, dependng on application of the car.
Some 4 wheel drive cars use a centre viscous coupling unit that will provide most power to the rear wheels unless the amount of torque being supplied to the rear wheels is in excess of the traction limits of the rear tyres, such as in a Lamborghini Murciélago. Others contain a computer that will decide how much power to distribute to any wheel at any time depending on the circumstances of each wheel. In general the M4 system is not widely used as it is suited toward sports cars and some off-road racing vehicles.
The engine is usually where the weight of a car is most concentrated so placing it between the front and rear axles gives a car a much better handling balance. Assuming the engine is behind the passenger compartment, the engine will also be pushing down on the rear wheels. Because the weight of a car is shifted toward the rear under acceleration in all cars as a rule, this further improves the amount of grip on the rear wheels, increasing the amount of torque that can be supplied to the rear wheels before wheelspin occurs. Because the engine is not in the front, the car can be designed with a minimum amount of frontal area perpendicular to the wind, greatly increasing aerodynamic efficiency.
A computer-controlled four-wheel-drive differential system allows a car to both accelerate and corner more quickly, since it can vary the amount of torque going to the front and rear wheels, and therefore vary how much the car behaves like a front- or rear-wheel-drive car. This means that through a fast corner the car is able to display more “neutral” handling – with less oversteer or understeer. This is a much more efficient means of turning and allows for faster cornering speeds as opposed to a two-wheel or conventional four-wheel-drive system. 
Such a system is very difficult and expensive to design and engineer, which is why it is only usually found on race cars and very expensive sports cars.
Most mid-engine cars, because of the size and position of the engine and transmission, compromise heavily on both passenger and boot/trunk space.
Four-wheel-drive systems tend to be quite heavy and some of the engine’s power can be lost through the various differentials in the car, in addition to the frictional losses of the powertrain.
The variable handling characteristics of a four-wheel-drive car mean that when travelling round a corner at high speeds the car may enter the corner and understeer and then half-way through the corner suddenly start to oversteer.
Posted on July 15, 2012, in General, Uncategorized and tagged 4x4, all wheel drive, automobile layouts, awd, boxer, cars, engine layouts, ff, FMR, four wheel drive, four wheel drive vehicles, fr, front engine, front wheel drive, fwd, longitudinally mounted, m4 layout, mid engine, mid engine all wheel drive, mid engine rear wheel drive, mr, porsche, rear engine, rear wheel drive, rwd, transportation, transversely mounted, type target, wheel drive vehicles, wikipedia the free encyclopedia. Bookmark the permalink. 1 Comment.