Automobile layout

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 for which the vehicle will be used. 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 layouts

Main article: front-wheel drive
FF layout

Front-wheel-drive layouts are those in which the front wheels of the vehicle are driven. The most popular layout used in cars today is the front-engine, front-wheel drive, with the engine in front of the front axle, driving the front wheels. This layout is typically chosen for its compact packaging; since the engine and driven wheels are on the same side of the vehicle, there is no need for a central tunnel through the passenger compartment to accommodate a prop-shaft between the engine and the driven wheels.

As the steered wheels are also the driven wheels, FF (front-engine, front-wheel-drive layout) cars are generally considered superior to FR (front-engine, rear-wheel-drive layout) cars in conditions such as snow, mud, or wet tarmac. The weight of the engine over the driven wheels also improves grip in such conditions. However, powerful cars rarely use the FF layout because weight transference under acceleration reduces the weight on the front wheels and reduces their traction, limiting the torque which can be utilized. Electronic traction control can avoid wheelspin but largely negates the benefit of extra torque/power.

A transverse engine (also known as "east-west") is commonly used in FF designs, in contrast to FR which uses a longitudinal engine. The FF layout also restricts the size of the engine that can be placed in modern engine compartments, as FF configurations usually have Inline-4 and V6 engines, while longer engines such as Inline-6 and 90° V8 will rarely fit. This is another reason luxury/sports cars avoid the FF layout. Exceptions do exist, such as the Volvo S80 (FWD/4WD) which uses transversely mounted inline 6 and V8 engines, and the Ford Taurus SHO, available with a 60° V8 and front-wheel drive.


Front-wheel drive gives more interior space since the powertrain is a single unit contained in the engine compartment of the vehicle and there is no need to devote interior space for a driveshaft tunnel or rear differential, increasing the volume available for passengers and cargo.[1] There are some exceptions to this as rear engine designs do not take away interior space (see Porsche 911, and Volkswagen Beetle). It also has fewer components overall and thus lower weight.[1] The direct connection between engine and transaxle reduces the mass and mechanical inertia of the drivetrain compared to a rear-wheel-drive vehicle with a similar engine and transmission, allowing greater fuel economy.[1] In front-wheel-drive cars the mass of the drivetrain is placed over the driven wheels and thus moves the centre of gravity farther forward than a comparable rear-wheel-drive layout, improving traction and directional stability on wet, snowy, or icy surfaces.[1][2][3] Front-wheel-drive cars, with a front weight bias, tend to understeer at the limit which, according to Saab engineer Gunnar Larsson, is easier since it makes instinct correct in avoiding terminal oversteer, and less prone to result in fishtailing or a spin.[3][4]

According to a sales brochure for the 1989 Lotus Elan, the ride and handling engineers at Lotus found that "for a given vehicle weight, power and tyre size, a front-wheel-drive car was always faster over a given section of road."[5] However, this may only apply for cars with moderate power-to-weight ratio.[2][6][7] According to road test with two Dodge Daytonas, one FWD and one RWD, the road layout is also important for what configuration is the fastest.[3]

Weight shifting limits the acceleration of a front-wheel-drive vehicle. During heavy acceleration, weight is shifted to the back, improving traction at the rear wheels at the expense of the front driving wheels; consequently, most racing cars are rear-wheel drive for acceleration. However, since front-wheel-drive cars have the weight of the engine over the driving wheels, the problem only applies in extreme conditions in which case the car understeers. On snow, ice, and sand, rear-wheel drive loses its traction advantage to front or all-wheel-drive vehicles which have greater weight over the driven wheels. Rear-wheel-drive cars with rear engine or mid engine configuration retain traction over the driven wheels, although fishtailing remains an issue on hard acceleration while in a turn. Some rear engine cars (e.g., Porsche 911) can suffer from reduced steering ability under heavy acceleration, since the engine is outside the wheelbase and at the opposite end of the car from the wheels doing the steering. A rear-wheel-drive car's centre of gravity is shifted rearward when heavily loaded with passengers or cargo, which may cause unpredictable handling behavior.[4]

On front-wheel-drive cars, the short driveshaft may reduce drivetrain elasticity, improving responsiveness.[4]



Rear-wheel-drive layouts

FR layout
RR layout

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 vehicles up until the 1970s and 1980s.[20] Nearly all motorcycles and bicycles use rear-wheel drive as well, 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.


The vast majority of rear-wheel-drive vehicles use a longitudinally mounted engine in the front of the vehicle, driving the rear wheels via a driveshaft linked via a differential between the rear axles. Some FR layout vehicles place the gearbox at the rear, though most attach it to the engine at the front.

The FR layout is often chosen for its simple design and good handling characteristics. Placing the drive wheels at the rear allows ample room for the transmission in the centre of the vehicle and avoids the mechanical complexities associated with transmitting power to the front wheels. For performance-oriented vehicles, the FR layout is more suitable than front-wheel-drive designs, especially with engines that exceed 200 horsepower. This is because weight transfers to the rear of the vehicle during acceleration, which loads the rear wheels and increases their grip.

Another advantage of the FR layout is relatively easy access to the engine compartment, a result of the longitudinal orientation of the drivetrain, as compared to the FF layout (front-engine, front-wheel drive). Powerful engines such as the Inline-6 and 90° big-bore V8 are usually too long to fit in a FF transverse engine ("east-west") layout; the FF configuration can typically accommodate at the maximum an Inline-4 or V6. This is another reason luxury/sports cars almost never use the FF layout.



Four-wheel-drive layouts

Front-engine, rear-wheel drive derived “F4” layout

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-engine and are derivatives of earlier front-engine, two-wheel-drive designs. They fall into two major categories:

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:


Unusual 4WD layouts

History and current use

FMR layout, standard in most Front-engine / Rear-wheel-drive cars pre-World War II, where the engine was located behind the front axle.

The first FR car was an 1895 Panhard model, so this layout was known as the "Système Panhard" in the early years. Most American cars used the FR layout until the mid-1980s. The Oil crisis of the 1970s and the success of small FF cars like the Mini, Volkswagen Golf, Toyota Tercel, and Honda Civic led to the widespread adoption of that layout.

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.[28] Chrysler went 100% FF by 1990 and GM's American production went entirely FF by 1997 except the Firebird, Corvette and Camaro. Ford's full-size cars (the Ford Crown Victoria, Mercury Grand Marquis, and Lincoln Town Car) have always been FR,[29] as was the Lincoln LS. In 2008 Hyundai introduced its own rear-wheel-drive car, the Hyundai Genesis.

In Australia, FR cars have remained popular throughout this period, with the Holden Commodore and Ford Falcon having consistently strong sales. In Europe, front-wheel drive was popularized by small cars like the Mini, Renault 5 and Volkswagen Golf and adopted for virtually 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.[30] Japanese mainstream marques such as Toyota and Nissan became mostly or entirely FF early on, while reserving for their latterly conceived luxury divisions (Lexus and Infiniti, respectively) a mostly FR lineup. While many automakers lost sight of the true sports car, Mazda introduced the highly successful Miata roadster in 1990, a true 2-seater sports car using the traditional FR layout which led to other compaines such as General Motors to produce a FR sports car based on their Kappa platform.

Currently most cars are FF, including virtually all front-engine 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 the FR luxury car with the 2003 Cadillac CTS, and with the removal of the DTS,[31] Cadillac will be entirely FR (with four-wheel drive available as an option on several models) by 2010, and the 2010 Camaro returns as a FR sports car. Chrysler returned its full-size cars to this layout with the Chrysler 300 and related models.[32][33] Despite Ford's 2011 discontinuation of the rear-wheel drive Panther Platform cars, they are seeking to develop a new FR replacement.[34] Nissan is also bringing back the Silvia to their line-up, Mazda is said to be releasing a new rotary-powered FR car in their RX line-up, and Toyota has produced the FT-86, an affordable RWD car which is the successor to the AE86. Hyundai introduced their affordable RWD car being the 2009 Hyundai Genesis and 2010 Hyundai Genesis Coupe.

In the 21st century, with solutions to the engineering complexities of 4WD being widely understood, and consumer demand for increasing performance in production cars, front-engine 4WD layouts are rapidly becoming more common, and most major manufacturers now offer 4WD options on at least some models. Manufacturers with a notable expertise and history in producing 4WD performance cars are Audi and Subaru.

See also


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  2. 1 2 3 William, Milliken (1995). "Merits of Front-, Rear-, and Four-Wheel Drive". Race Car Vehicle Dynamics. SAE International. p. 730. ISBN 1-56091-526-9. Front-wheel drive has been most successful in the lower power/weight range and in situations in which superior directional stability on low coefficients is important. There has never been a successful front-drive Grand Prix car nor a competitive Indianapolis car of more than 300 hp.
  3. 1 2 3 4 5 6 "What's It Like To Drive", describes a test between two Dodge Daytonas, one FWD and one RWD
  4. 1 2 3 4 5 6 "The Hidden Virtues of Front Wheel Drive". Saab Automobile.
  5. Lotus Elan M100 Sales Manual
  6. Frere, Paul (1992). "From Slipping to Sliding". Sports Car and Competition Driving. entleyPublishers. p. 67pp. ISBN 0-8376-0202-5. Front-wheel drive which, due to the reduced front wheel grip under acceleration, is practical only for cars of moderate power-to-weight ratio
  7. Prost, Alain (1990). "Controlling a car at the limit". Competition Driving. Hazelton Publishing. p. 50pp. ISBN 0-905138-80-5. Front-wheel drive. In this instance, both power and steering are directed through the front wheels, the rears remaining free. Following the principle of weight transfer once more, the lightening of the front wheels under acceleration considerably reduces their effectiveness and thus limits the usable power. Consequently, this type of transmission is generally less effective on racing circuits, a few exceptions notwithstanding, but has its advantages in road events where maximum power is not called into play so often
  8. Kenwright, Joe (2010-04-15). "Driving Wheels - Front, Rear or All-Wheel Drive?". CarPoint. Retrieved 2010-05-06.
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  10. Wiesenfelder, Joe (2009-11-06). "2010 Audi S4". Retrieved 2012-12-09.
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  12. Quiroga, Tony (August 2010). "2011 Audi RS5 vs. 2010 BMW M3, 2011 Cadillac CTS-V Comparison Tests". Car and Driver. Retrieved 2012-12-09.
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  30. Automaker Ratings
  31. "Cadillac DTC to be discontinued". Drive Your Dream Blog. US. 2007-10-02. Archived from the original on 2008-12-03.
  32. Chrysler brings back rear-wheel drive. - By Mickey Kaus - Slate Magazine
  33. 2011 Chrysler 300, Dodge Charger to remain rear-wheel drive
  34. | This article is no longer available online
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