Rear-wheel drive

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Rear-wheel drive (or RWD for short) was a common engine/transmission layout used in automobiles throughout the 20th century. RWD typically places the engine in the front of the vehicle, but the mid engine and rear engine layouts are also used.

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 1980s, due in part to higher manufacturing costs, and a perception by many car buyers that front wheel drive is safer, and that it performs better on slippery roads.

It still sees heavy use in taxi and police fleets, due to cheaper maintenance, and in the case of police fleets, better performance.

Advantages

  • Better handling in dry conditions - accelerating force is applied to the rear wheels, on which the down force increases, due to load transfer in acceleration, making the rear tires better able to take simultaneous acceleration and curving than the front tires.
  • Less costly and easier maintenance - Rear wheel drive is mechanically simpler and typically does 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 to replace parts.
  • Even weight distribution - The division of weight between the front and rear wheels has a significant impact on a car's handling, and it is much easier to get a 50/50 weight distribution in a rear wheel drive car than in 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.
  • 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.
  • Weight transfer during acceleration. (During heavy acceleration, the front end rises, and more weight is placed on the rear, or driving wheels).
  • Drifting - Drifting is a controlled skid, where the rear wheels break free from the pavement as they spin, allowing the rear end of the car to move freely left and right. This is of course easier to do on slippery surfaces. Severe damage and wear to tires and mechanical components can result from drifting on dry asphalt. Drifting can be used to help in cornering quickly, or in turning the car around in a very small space. Many enthusiasts make a sport of drifting, and will drift just for the sake of drifting. Drifting requires a great deal of skill, and is not recommended for most drivers. It should be mentioned that front wheel drive and four wheel drive cars may also drift, but only with much more difficulty. When front wheel drive cars drift, the driver usually pulls on the emergency brake in order for the back wheels to stop and thus skid. This technique is also used for 'long' drifts, where the turn is accomplished by pulling the e-brake while turning the steering wheel to the direction the driver desires. With drifting, there is also the importance of 'counter-steering' - where while temporarily out of control, the driver regains it by turning the wheel in the opposite direction and thus preparing for the next turn or straight-away.

Disadvantages

  • More difficult to master - While the handling characteristics of rear-wheel drive may be useful or fun in the hands of some drivers, for others, having the rear wheels move about is unintuitive and dangerous. Rear wheel drive rewards skill, and punishes the lack of it. Other layouts are much more forgiving, but don't offer the same rewards in handling.
  • Decreased interior space - This isn't an issue in a vehicle with a ladder frame like a pickup truck, where the space used by the drive line is unusable for passengers or cargo. But in a passenger car, rear wheel drive means: Less front leg room (the transmission tunnel takes up a lot of 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).
  • Increased weight - The components of your typical rear wheel drive vehicle's power train may be less complex, but there are more of them. The driveshaft adds weight. The transmission is probably heavier. There is extra sheet metal to form the transmission tunnel. There is a rear axle or rear half-shafts. A rear wheel drive car will weigh slightly more than a comparable front wheel drive car (but less than four wheel drive).
  • Higher purchase price - Probably due to more complicated 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, however.
  • More difficult handling on low grip surfaces (wet road, ice, snow, gravel...) as the car is pushed rather than pulled. This can make driving up a hill difficult. It can also lead to accidents in light rain. The decline in popularity of rear wheel drive cars can be attributed to these factors.

Current or recent rear wheel drive cars to 2006

While the popularity of rear wheel drive has declined, it is still relatively prevalent, and has been making something of a resurgence. Here is list of current or recent rear wheel drive vehicles. See also Category:Rear wheel drive vehicles.

External links


Automobile layouts
Layouts:
FF | FMR | FR | MF | RMR | RR | F4
Engine positioning:
Front-engine | Mid-engine | Rear-engine
Drive:
Front-wheel drive | Rear-wheel drive | Four-wheel drive | Six-wheel drive
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