rear-wheel drive

Information about rear-wheel drive

Rear-wheel drive (or RWD for short) is the most common Internal combustion engine/transmission layout used in automobiles. RWD typically places the engine in the front of the vehicle, but the front mid-engine, rear mid-engine and rear engine layouts are also used. Rear-wheel drive is used almost universally for driving motorcycles, whether by driveshaft, chain, or belt. 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 transmission at the rear, though most attach it to the engine at the front. Rear wheel drive has fallen out of favor in passenger cars since the late 1980s, due in part to higher manufacturing costs, and that front wheel drive is safer for a driver of average ability[1], and that it performs better on slippery roads.[2][3] However, some automobile brands, including Lincoln, Mercedes-Benz, BMW, Lexus, and Porsche continue to use rear wheel drive platforms. Rear wheel drive (or all-wheel drive) is still the preferred choice for high performance automobiles, due to the fact that very powerful front wheel drive cars tend to understeer.[4] The general limit of controllable power for a front wheel drive car is generally placed between 230 and 300 horsepower.

Advantages

  • Even weight distribution - The layout of a rear wheel drive car is much closer to an even fore and aft weight distribution than a front wheel drive car, as more of the engine can lie between the front and rear wheels (in the case of a mid engine layout, the entire engine), and the transmission is moved much farther back.[5]
  • Weight transfer during acceleration - During heavy acceleration, weight is placed on the rear, or driving wheels, which improves traction.
  • No torque steer<ref name="forza" /> (unless it's an all wheel steer with an offset differential).
  • Steering radius - As no complicated drive shaft joints are required at the front wheels, it is possible to turn them further than would be possible using front wheel drive, resulting in a smaller steering radius for a given wheelbase.
  • Better handling in dry conditions - the more even weight distribution and weight transfer improve the handling of the car. The front and rear tires are placed under more even loads, which allows for more grip while cornering.[1]
  • Better braking - the more even weight distribution helps prevent lockup from wheels becoming unloaded under heavy braking.[1]
  • Towing - Rear wheel drive puts the wheels which are pulling the load closer to the point where a trailer articulates, helping steering, especially for large loads.[1]
  • Serviceability - Drivetrain components on a rear-wheel drive vehicle are modular and do not involve packing as many parts into as small a space as does front wheel drive, thus requiring less disassembly or specialized tools in order perform servicing.
  • Robustness - due to geometry and packaging constraints, the CV joints attached to the wheel hub have a tendency to wear out much earlier than the universal joints typically used in their rear-wheel drive counterparts. The significantly shorter drive axles on a front-wheel drive car causes the joint to flex through a much wider degree of motion, compounded by additional stress and angles of steering, while the CV joints of a rear wheel drive car regularly see angles and wear of less than half that of front wheel drive vehicles.

Disadvantages

  • Oversteer and the related problem of fishtailing.
  • On snow, ice and sand, rear-wheel drive loses its traction advantage to front or all-wheel drive vehicles which have greater weight on the driven wheels. Rear wheel drive cars with rear engine or mid engine configuration do not suffer from this, although fishtailing remains an issue.
  • Some rear engine cars (e.g. Porsche 911) can suffer from reduced steering ability under heavy acceleration, because the engine is outside the wheelbase and at the opposite end of the car from the wheels doing the steering.
  • Decreased interior space - In a passenger car, rear wheel drive means: Less front leg room as the transmission tunnel takes up a space between the driver and front passenger, less leg room for center rear passengers (due to the tunnel needed for the drive shaft), and sometimes less trunk space (since there is also more hardware that must be placed underneath the trunk). There are some exceptions to this as rear engine designs do not take away interior space. (See Porsche 911, and Volkswagen Beetle)
  • Increased weight - The components of a rear wheel drive vehicle's power train are less complex, but they are larger. The driveshaft adds weight. There is extra sheet metal to form the transmission tunnel. There is a rear axle or rear half-shafts, which are typically longer than those in a front-wheel drive car. A rear wheel drive car will weigh slightly more than a comparable front wheel drive car (but less than four wheel drive).
  • Improper weight distribution when loaded - A rear wheel drive car's center of gravity is shifted rearward when heavily loaded with passengers or cargo, which may cause unpredictable handling behavior.[2]
  • Higher initial purchase price - Probably due to more complex assembly (the powertrain is not one compact unit) and added cost of materials, rear wheel drive is typically slightly more expensive to purchase than a comparable front wheel drive vehicle. This might also be explained by production volumes, or the fact that the majority of rear-wheel cars are in the sports/performance/luxury categories. Few "family" sedans have rear-wheel drive, so a cost comparison is not necessarily possible.
  • The possibility of a slight loss in the mechanical efficiency of the drivetrain (approximately 17% coastdown losses between engine flywheel and road wheels compared to 15% for front wheel drive - these losses are highly dependent on the individual transmission, and the source should be cited). Cars with rear engine or mid engine configuration and a transverse engine layout do not suffer from this.
  • The long driveshaft (on FR cars) adds to drivetrain elasticity.[2]

Current or recent rear wheel drive cars to 2006

While the popularity of rear wheel drive has declined since the early 1980s, it is still relatively common, and has been making something of a resurgence. Here is list of current or recent rear wheel drive vehicles. See also .

References

External links

  •  • [ e] Automobile layout
Layouts: FF, FMR, FR, MF, RMR, RR, F4, M4, R4
Engine positioning: Front-engine, Mid-engine, Rear-engine
Drive: Front-wheel drive, Rear-wheel drive, Four-wheel drive, Six-wheel drive
range of input/output ratios in addition to its infinite number of possible ratios; this qualification for the IVT implies that its range of ratios includes a zero output/input ratio that can be continuously approached from a defined 'higher' ratio.
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automobile (from Greek auto, self and Latin mobile moving, a vehicle that moves itself rather than being moved by another vehicle or animal) or motor car (usually shortened to just car) is a wheeled passenger vehicle that carries its own motor.
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The FMR layout, standing for front mid-engine, rear wheel drive, is a layout of an automobile that places the engine in the front, like the FR layout, but pushed back enough that the engine's center of gravity is to the rear of the front axle.
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RMR or Rear 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 mass of the engine is in front of the rear axle.
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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, however, the center of gravity of the engine itself is actually past the rear axle.
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MotorCycle
(1993) BibleLand
(1994)

MotorCycle is the title of a 1993 album by rock band Daniel Amos, released on BAI Records. The album was dedicated to the memory of songwriter Mark Heard.
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driveshaft, driving shaft, or Cardan shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied. Most engines or motors deliver power as torque through rotary motion: this is extracted from the linear motion
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Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles. It is also used in a wide variety of machines besides vehicles.
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Belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. They may be used as a source of motion, to efficiently transmit power, or to track relative movement.

Belts are looped over pulleys.
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longitudinal engine, also sometimes known as a north-south engine, is an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicle, front to back.
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driveshaft, driving shaft, or Cardan shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied. Most engines or motors deliver power as torque through rotary motion: this is extracted from the linear motion
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differential is a device, usually consisting of gears, that allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them.

Purpose

A vehicle's wheels rotate at different speeds, especially when turning corners.
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FR, or front-engine, rear wheel drive means a layout where the engine is in the front of the vehicle and drive wheels at the rear. This was the traditional automobile layout for most of the 20th century.
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Front-wheel drive 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
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The now widespread name Lincoln originated in a city in eastern England, UK. Its name is a contraction of the Latin Lindum Colonia, which was the name of a colony for veteran Roman soldiers.
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For other uses of the name Mercedes, see Mercedes.

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Bayerische Motoren Werke AG

Aktiengesellschaft
Founded 1916
Headquarters Munich, Germany

Key people Dr. Norbert Reithofer, Chairman and CEO
Industry Automotive
Products Automobiles
Motorcycles
Revenue €49 billion (2006)
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Lexus

Luxury division
Founded 1989
Founder Eiji Toyoda
Headquarters Toyota, Aichi, Japan
Torrance, California, USA

Key people Takeshi Yoshida, Managing Officer, Lexus Division
Jim Farley, Vice President and General Manager, Lexus Group
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Dr Ing. h.c. F. Porsche AG

Public
(Xetra: POR3 )
(FWB: POR3 )
Founded 1931 by Ferdinand Porsche and Ferry Porsche
Headquarters Zuffenhausen, Germany

Key people Dr.
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Supercar is a term used for a high-end sports car, typically an exotic or rare one, whose performance is highly superior to that of its contemporaries. The proper application of the term is subjective and disputed, especially among enthusiasts.
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Understeer is a term for a car handling condition during cornering in which the circular path of the vehicle's motion is of a markedly greater diameter than the circle indicated by the direction its wheels are pointed.
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A mid-engine layout describes the placement of an automobile engine between the rear and front axles. Another term for this is mid-ship, though that term is used mostly by British and Japanese manufacturers.
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Traction may refer to:
  • Traction (engineering), the mechanical force used to achieve motion
  • Railway electric traction, the use of electric motors to propel rail cars

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Torque steering is the influence of the engine torque on the steering for some front-wheel drive vehicles. For example, during full acceleration the steering may pull to one side, which may be disturbing to the driver.
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Car handling and vehicle handling is a description of the way wheeled vehicles perform transverse to their direction of motion, particularly during cornering and swerving. It also includes their stability when moving in a straight line.
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Constant Velocity Joints (aka homokinetic or CV joints) allow a rotating shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play.
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A universal joint, U joint, Cardan joint, Hardy-Spicer joint, or Hooke's joint is a joint in a rigid rod that allows the rod to 'bend' in any direction.
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Oversteer is a phenomenon that can occur in an automobile which is attempting to turn. The car is said to oversteer when the rear wheels do not track behind the front wheels but instead slide out toward the outside of the turn. Oversteer can throw the car into a spin.
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