Rear-wheel drive: Difference between revisions

Content deleted Content added

Inline

Revision as of 06:04, 12 May 2008

Rear-wheel drive (or RWD for short) is a common 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^{[citation needed]}. This was most often due to higher manufacturing costs. Some automobile brands, including Lincoln, Mercedes-Benz, BMW, Lexus, Holden Tomcar, Porsche, and latest, Hyundai retain rear wheel drive platforms. Rear wheel drive is the preferred two-wheel drive choice for high performance automobiles because powerful front wheel drive cars understeer^[1] more severely, and the ability to fit a large engine in a front-wheel drive layout while maintaining good fore and aft weight distribution is limited. The limit of controllable power for a front wheel drive car is generally placed between 230 and 300 horsepower^{[citation needed]}.

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.^[2]
Weight transfer during acceleration - During heavy acceleration, weight is placed on the rear, or driving wheels, which improves traction.
No torque steer^[1] (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.^[3]
Better braking - the more even weight distribution helps prevent lockup from wheels becoming unloaded under heavy braking.^[3]
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.^[4]
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.^{[citation needed]}
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.^{[citation needed]}

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 although the engine weight over the rear wheels provides outstanding traction and grip during acceleration.
Decreased interior space - Though individual designs vary greatly, rear wheel drive vehicles may have: 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). Rear engine designs (such as the Porsche 911 and Volkswagen Beetle) do not inherently take away interior space.
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.^[5]
Higher initial purchase price - Modern rear wheel drive vehicles are typically slightly more expensive to purchase than comparable front wheel drive vehicles. Although the complex assembly (the powertrain is not one compact unit) and added cost of materials, this cost difference is more probably explained by production volumes and the fact that the majority of rear-wheel cars are in the sports/performance/luxury categories. Few modern "family" sedans have rear-wheel drive, so a cost comparison is not necessarily possible.^{[citation needed]}
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^{[citation needed]} - however these losses are highly dependent on the individual transmission). Cars with rear engine or mid engine configuration and a transverse engine layout do not suffer from this.
The long driveshaft (on front engine cars) adds to drivetrain elasticity.^[5] The driveshaft must also be extended for cars with a stretched wheelbase (e.g. limousines, minivans).

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 Category:Rear wheel drive vehicles.

Nearly all two-wheel drive trucks and most sport utility vehicles are rear wheel drive.

Alfa Romeo - Alfa 8C
Aston Martin - All models
Bentley - Arnage, Azure
BMW - All models except the MINI, and all-wheel drive variants
Cadillac - All models except DTS, BLS and all-wheel drive variants
Chevrolet - Corvette, Camaro
Chrysler - 300, Crossfire
Dodge - Viper, Charger, Magnum, Challenger,Durango
Ferrari - All models
FIAT - 126p, 131,
Ford - Crown Victoria, Falcon (Australia), Fairlane (Australia), Mustang, Thunderbird, Sierra, Scorpio
FSO - Polonez
GMC - All models except Acadia and four-wheel drive variants
Holden - Commodore (all models), Statesman / Caprice, Monaro, HSV Clubsport R8
Honda - S2000, NSX, Beat,
Hyundai- Genesis, Genesis Coupe
Infiniti - All models except all-wheel drive variants, I30, I35 and G20
Jaguar - All except X-Type
Jeep - All models except Compass and four-wheel drive variants
Lexus - All cars except ES, RX, and all-wheel drive variants
Lincoln - Town Car, LS
Lotus - All cars except Elan M100
Maserati - All models
Mazda - MX-5 Miata, RX-7, RX-8, 929
Mercedes-Benz - All cars except A-Class, B-Class and all-wheel drive models
Mercury - Grand Marquis, Marauder
MG - MG F, MG TF, MG ZT (260+), MG XPower SV
Morgan - All models
Nissan - 350Z, Cefiro (except 4WD models), Skyline (except 4WD models),Silvia, 180SX, 200SX, 240SX, 300ZX
Peugeot ROA
Pontiac - GTO, Solstice, G8, Firebird, Trans Am
Porsche - All cars except the four-wheel drive 911 Carrera 4, 911 Turbo and Cayenne
Saturn - Sky
Smart - Fortwo, Roadster
Tata - Nano
Tesla Motors - Tesla Roadster
Tofaş - Şahin, Doğan, Kartal, Serçe
Toyota - Altezza, Crown, Hilux (RWD and 4WD), Mark X, MR2, Supra, Tacoma (RWD and 4WD)
TVR - All models
Vauxhall - Vauxhall VXR8, Vauxhall Omega

References

^ ^a ^b Che Chou. "FWD vs. RWD". Forza Motorsport 2.
^ Jim Kerr. "Front wheel drive vs rear wheel drive". Canadian Driver.
^ ^a ^b Cite error: The named reference family was invoked but never defined (see the help page).
^ Michael Vatalaro. "SUVs carry the load". Boat/US Magazine.
^ ^a ^b Cite error: The named reference hidden was invoked but never defined (see the help page).

Opel Omega A,B

External links

RearWheelDrive.org - An organization that is devoted to promote RWD
"Why Front-Wheel Drive Sucks - And Why Rear-Wheel Drive is Coming Back" - A personal opinion
What's It Like To Drive - Describes a test between two Dodge Daytonas, one FWD and one RWD

[forza-1] Che Chou. "FWD vs. RWD". Forza Motorsport 2.

[2] Jim Kerr. "Front wheel drive vs rear wheel drive". Canadian Driver.

[family-3] Cite error: The named reference family was invoked but never defined (see the help page).

[tow-4] Michael Vatalaro. "SUVs carry the load". Boat/US Magazine.

[hidden-5] Cite error: The named reference hidden was invoked but never defined (see the help page).

[1]

[2]

[3]

[4]

[5]

@@ Line 7: / Line 7: @@
 The vast majority of rear wheel drive vehicles use a [[Longitudinal engine|longitudinally-mounted engine]] in the front of the vehicle, driving the rear wheels via a [[driveshaft]] linked via a [[differential (mechanics)|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]]{{Fact|date=February 2007}}<!-- Not a [[WP:RS]] <ref>{{cite web |url=http://www.mrfizzix.com/autoracing/drivetrains.htm |title=Drivetrains}}</ref> -->. This might be due in part to higher manufacturing costs, and the fact that [[front wheel drive]] is safer for a driver of average ability<ref name="family">[http://www.familycar.com/NextCar/Step3.htm The Family Car: Front wheel drive, rear wheel drive, or all wheel drive?]</ref>. Also, a front wheel drive car performs better on slippery roads.<ref name="hidden">[http://www.saabnet.com/tsn/models/1984/pr2.html The Hidden Virtues of Front Wheel Drive]</ref><ref>[http://findarticles.com/p/articles/mi_m0BQK/is_5_10/ai_n15393977 SUVs carry the load]</ref> However, some automobile brands, including [[Lincoln (automobile)|Lincoln]], [[Mercedes-Benz]], [[BMW]], [[Lexus]], [[Holden]] [[Tomcar]], [[Porsche]], and latest, [[Hyundai]] use rear wheel drive platforms.  Rear wheel drive (or, alternately, all-wheel drive) is still the preferred choice for [[Supercar|high performance]] automobiles because very powerful front wheel drive cars tend to [[understeer]]<ref name="forza">{{cite web |url=http://forzamotorsport.net/121306-1.htm |title=FWD vs. RWD |publisher=Forza Motorsport 2 |author=Che Chou}}</ref>, and the ability to fit a large engine in a front-wheel drive layout while maintaining good fore and aft weight distribution is limited. The limit of controllable power for a front wheel drive car is generally placed between 230 and 300 horsepower{{Fact|date=April 2008}}.
+Rear wheel drive has fallen out of favor in passenger cars since the late [[1980s]]{{Fact|date=February 2007}}<!-- Not a [[WP:RS]] <ref>{{cite web |url=http://www.mrfizzix.com/autoracing/drivetrains.htm |title=Drivetrains}}</ref> -->. This was most often due to higher manufacturing costs. Some automobile brands, including [[Lincoln (automobile)|Lincoln]], [[Mercedes-Benz]], [[BMW]], [[Lexus]], [[Holden]] [[Tomcar]], [[Porsche]], and latest, [[Hyundai]] retain rear wheel drive platforms. Rear wheel drive is the preferred two-wheel drive choice for [[Sports car|high performance automobiles]] because powerful front wheel drive cars [[understeer]]<ref name="forza">{{cite web |url=http://forzamotorsport.net/121306-1.htm |title=FWD vs. RWD |publisher=Forza Motorsport 2 |author=Che Chou}}</ref> more severely, and the ability to fit a large engine in a front-wheel drive layout while maintaining good fore and aft weight distribution is limited. The limit of controllable power for a front wheel drive car is generally placed between 230 and 300 horsepower{{Fact|date=April 2008}}.
 ==Advantages==
@@ Line 13: / Line 13: @@
 * 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.<ref>{{cite web|url=http://www.canadiandriver.com/winter/020619.htm|title=Front wheel drive vs rear wheel drive|author=Jim Kerr|publisher=Canadian Driver}}</ref>
 * [[Weight transfer]] during acceleration - During heavy acceleration, weight is placed on the rear, or driving wheels, which improves [[traction]].
 * No [[Torque steering|torque steer]]<ref name="forza" /><!-- Not a [[WP:RS]] <ref>{{cite web |url=http://www.everything2.com/index.pl?node_id=1174269 |title=Torque Steer}}</ref>--> (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 [[Car handling|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.<ref name="family"/>
 * Better braking - the more even weight distribution helps prevent lockup from wheels becoming unloaded under heavy braking.<ref name="family"/>
+* 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.<ref name="tow">{{cite web |url=http://findarticles.com/p/articles/mi_m0BQK/is_5_10/ai_n15393977 |title=SUVs carry the load |publisher=Boat/US Magazine |author=Michael Vatalaro}}</ref>
-* 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.<ref name="family"/>
 * 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.{{Fact|date=February 2007}}<!-- Not a [[WP:RS]] <ref name="rwdorg"/> -->
 * Robustness - due to geometry and packaging constraints, the [[constant-velocity joint|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.{{Fact|date=February 2007}}<!-- What about MR and RR configurations? -->
 ==Disadvantages==
 {{Mergeto|Automobile layout|date=April 2007}}
 * [[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 although the engine weight over the rear wheels provides outstanding traction and grip during acceleration.
 * Decreased interior space - Though individual designs vary greatly, rear wheel drive vehicles may have: 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).  [[Rear engine]] designs (such as the [[Porsche 911]] and [[Volkswagen Beetle]]) do not inherently take away interior space.
 * 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.<ref name="hidden"/>
 * Higher initial purchase price - Modern rear wheel drive vehicles are typically slightly more expensive to purchase than comparable front wheel drive vehicles. Although the complex assembly (the [[powertrain]] is not one compact unit) and added cost of materials, this cost difference is more probably explained by [[economy of scale|production volumes]] and the fact that the majority of rear-wheel cars are in the sports/performance/luxury categories. Few modern "family" sedans have rear-wheel drive, so a cost comparison is not necessarily possible.{{Fact|date=February 2007}}
 * 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{{Fact|date=March 2008}} - however these losses are highly dependent on the individual transmission). Cars with [[rear engine]] or [[mid engine]] configuration and a transverse engine layout do not suffer from this.
 * The long [[driveshaft]] (on front engine cars) adds to drivetrain elasticity.<ref name="hidden"/> The driveshaft must also be extended for cars with a stretched wheelbase (e.g. limousines, minivans).
 ==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 [[:Category:Rear wheel drive vehicles]].