View source for Engineering:Rear-engine, rear-wheel-drive layout

{{Short description|Automotive design}}
[[File:Automotive diagrams 05 En.png|thumb|275px|RR layout]]

In [[Engineering:Automotive design|automotive design]], an '''RR''', or '''[[Engineering:Rear-engine design|rear-engine]], rear-wheel-drive layout''' places both the [[Earth:Internal combustion engine|engine]] and drive wheels at the rear of the vehicle. In contrast to the [[Engineering:Rear mid-engine, rear-wheel-drive layout|RMR layout]], the [[Physics:Center of mass|center of mass]] of the engine is between the rear axle and the rear bumper. Although very common in [[Engineering:Transit bus|transit buses]] and coaches due to the elimination of the [[Engineering:Drive shaft|drive shaft]] with [[Engineering:Low-floor bus|low-floor buses]], this layout has become increasingly rare{{specify}} in [[Engineering:Car|passenger cars]].<ref>[http://significantcars.com/cars/1965chevrolet3/ 1965 Chevrolet Corvair]</ref>

==Overview==
[[File:Mercedes-Benz_O500LE_chassis_on_display_at_the_2013_Australian_Bus_&_Coach_Show_(1).jpg|thumb|Mercedes-Benz O500LE coach chassis showing the engine located far behind the rear axle]]
Most of the traits of the RR configuration are shared with the mid-engine rear-wheel-drive, or MR. Placing the engine near the driven rear wheels allows for a physically smaller, lighter, less complex, and more efficient drivetrain, since there is no need for a driveshaft, and the [[Engineering:Differential (mechanical device)|differential]] can be integrated with the transmission, commonly referred to as a [[Engineering:Transaxle|transaxle]]. The front-engine front-wheel-drive layout also has this advantage.

Since the engine is typically the heaviest component of the car, putting it near the rear axle usually results in more weight over the rear axle than the front, commonly referred to as a rear weight bias. The farther back the engine, the greater the bias. Typical weight bias for an FF (front engine, front-wheel-drive) is 65/35 front/rear; for FR, 55/45; for MR, 45/55; for RR, 35/65. A static rear weight requires less forward brake bias, as load is more evenly distributed among all four wheels under braking. Similarly, a rear weight bias means that the driven wheels have increased traction when accelerating, allowing them to put more power on the ground and accelerate faster.

The disadvantage to a rear weight bias is that the car can become unstable and tend to oversteer, especially when decelerating (whether braking or lifting off the throttle; see [[Engineering:Lift-off oversteer|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.

Under hard acceleration, the decreased weight over the front wheels means less traction, sometimes producing a tendency for rear-engined cars to understeer out of a corner.

In these respects, an RR can be considered to be an exaggeration of MR - harder braking, faster and earlier acceleration, and increased oversteer.

In off-road and low-traction situations, the RR layout has some advantages compared to other 2WD layouts. The weight is biased towards the driven wheels- as with FF vehicles. This both improves drive-wheel traction and reduces the tendency for the undriven wheels to dig in. In addition, the driving and steering requirements are split between front and rear- as with FR vehicles- making it less likely for either to lose traction. Many [[Engineering:Dune buggy|dune buggies]] successfully use a Volkswagen beetle as the donor car for this reason. The relative simplicity and light weight compared to 4WD can therefore sometimes outweigh the disadvantage of only having two driven wheels.<ref>[https://de.gta5-mods.com/vehicles/semi-realistic-handling-for-greenaid-s-1974-vw-beetle Semi Realistic Handling 1974 VW Beetle] </ref><ref>[https://carbiketech.com/rear-engine-layout-beneficial/ Technical Anatomy, What is Rear Engine Layout And Know How Is It Beneficial?, January 5,2018]</ref>

Where RR differs from MR is in that the engine is located outside the wheelbase. The major advantage of MR - low moment of inertia - is negated somewhat (though still lower than FR), and there is more room for passengers and cargo (though usually less than FR). Furthermore, because both axles are on the same side of the engine, it is technically more straightforward to drive all four wheels, than in a mid-engined configuration (though there have been more high-performance cars with the M4 layout than with R4). Finally, a rear-mounted engine has empty air (often at a lower pressure) behind it when moving, allowing more efficient cooling for air-cooled vehicles (more of which have been RR than liquid-cooled, such as the [[Engineering:Volkswagen Beetle|Volkswagen Beetle]], and one of the few production air-cooled turbocharged cars, the [[Engineering:Porsche 930|Porsche 930]]).

For liquid-cooled vehicles, however, this layout presents a disadvantage, since it requires either increased coolant piping from a front-mounted radiator (meaning more weight and complexity), or relocating the radiator(s) to the sides or rear, and adding air ducting to compensate for the lower airflow at the rear of the car.

Due to the handling difficulty, the need for more space efficiency, and the near ubiquitous use of [[Physics:Water cooling|liquid-cooled]] engines in modern cars, most manufacturers have abandoned the RR layout. The major exception is [[Company:Porsche|Porsche]], who has developed the [[Engineering:Porsche 911|911]] for over 40 years and has taken advantage of the benefits of RR while mitigating its drawbacks to acceptable levels, lately with the help of electronic aids.
<ref>[https://petrolicious.com/articles/why-is-the-chevrolet-corvair-such-an-overlooked-classic Why Is The Chevrolet Corvair Such An Overlooked Classic?, By Andrew Golseth, February 12, 2016]</ref>

==History==
One of first RR cars was [[Engineering:Tatra 77|Tatra 77]] of 1934, the first serial-produced aerodynamic car, designed by Hans Ledwinka. [[Company:Tatra|Tatra]] used this layout until end of production of [[Engineering:Tatra 700|T700]] in 1999. In case of [[Engineering:Tatra 613|T613]] and [[Engineering:Tatra 700|T700]] Tatra used layout with engine above rear axle, which reduced some disadvantages of RR layout. Mercedes-Benz also produced several models of RR cars in this period, starting with the [[Engineering:Mercedes-Benz 130|130H]] (1934). The radical 1930s Tatra format (air-cooled, rear engine and streamlined, teardrop design) was an influence on Ferdinand Porsche's 'People's Car' ([[Engineering:Volkswagen Beetle|Volkswagen]]) for Adolf Hitler. As well as being the most produced car ever, it set a trend for RR small cars that lasted well into the 1960s. The final form of the RR Volkswagen was the [[Engineering:Volkswagen Type 3|Type 3]] of 1961, which flattened the engine (or 'pancake'), allowing for luggage spaces front and rear.

[[Company:Porsche|Porsche]] has continued to develop its [[Engineering:Porsche 911|911]] model as a rear-engined vehicle, although they have introduced multiple [[Engineering:Four-wheel drive|all-wheel-drive]] models. Most notably, the 911 Turbo has been sold as AWD-only since the release of the [[Engineering:Porsche 993|993]] model. Race-oriented models such as the [[Engineering:Porsche 911 GT3|GT3]] and twin-turbocharged [[Engineering:Porsche 911 GT2|GT2]] remain solely RR, however.<ref>[https://arstechnica.com/cars/2015/08/porsche-911-52-years-of-staying-true-to-its-roots/ arstechnica.com, Porsche 911: 52 years of staying true to its roots, First unveiled in 1963, the Porsche 911 has only ever been fully redesigned twice., Jonathan M. Gitlin, 8/18/2015]</ref>

Another manufacturer to implement the RR configuration was the [[Company:DeLorean Motor Company|DeLorean Motor Company]] with its [[Engineering:DMC DeLorean|DeLorean]] sports car. To compensate for the uneven (35/65) weight distribution caused by the rear-mounted engine, De Lorean used rear wheels with a diameter slightly greater than the front wheels. Before that was the rear-engined Škoda's from Škoda 1000MB (produced from 1964) to Škoda 130/135/136 (produced until 1990)  or the Polski Fiat 126p (produced until October 2000).

A range of sports road cars and racing cars with the RR layout was produced by the French company Alpine.  These had bodies made of [[Chemistry:Composite material|composite material]]s and used mechanical components made by Renault.  (Alpine was eventually acquired by Renault; the A610 was a Renault product that used the Alpine name.)

Early cars using the RR layout included the Tucker, [[Engineering:Volkswagen Beetle|Volkswagen Beetle]], [[Engineering:Porsche 356|Porsche 356]], [[Engineering:Chevrolet Corvair|Chevrolet Corvair]], [[Engineering:NSU Prinz|NSU Prinz]], [[Engineering:ZAZ Zaporozhets|ZAZ Zaporozhets]] and [[Engineering:Hino Contessa|Hino Contessa]].

==Present day==
Examples of modern [[Earth:Internal combustion engine|combustion engine]] cars using the layout include the [[Engineering:Porsche 911|Porsche 911]], [[Engineering:Mitsubishi i|Mitsubishi i]], [[Engineering:Smart Forfour|Smart Forfour]], and [[Engineering:Renault Twingo|Renault Twingo]].<ref>[http://timesofindia.indiatimes.com/Business/India_Business/Specifications_of_Tatas_Nano/articleshow/2690208.cms Specifications of Tata's Nano-India Business-Business-The Times of India<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20081012173658/http://timesofindia.indiatimes.com/Business/India_Business/Specifications_of_Tatas_Nano/articleshow/2690208.cms |date=October 12, 2008 }}</ref>

Many modern [[Engineering:Electric car|electric car]]s use an RR layout for base variants with a single motor due to the low weight and cooling requirements of the [[Physics:Electric motor|electric motor]]. The [[Engineering:Tesla Cybertruck|Tesla Cybertruck]] and [[Engineering:GMC Hummer EV|GMC Hummer EV]] will also use this layout for their base variants.

Most modern heavy duty buses use an extreme RR layout. In [[Engineering:Transit bus|transit bus]]es this can be used to make a very low floor level in the first two-thirds of the bus, thus making disabled access much easier.

Most tour buses and coaches also employ a similar design, however the free space is usually used for luggage, and sometimes airconditioning equipment.

==Examples==
<gallery perrow="7">
File:BMW i3 24.06.19 JM.jpg|[[Engineering:BMW i3|BMW i3]], a rear wheel drive, rear motor electric vehicle
File:Tatra 77A dutch licence registration AM-44-01 pic10.JPG|[[Engineering:Tatra 77|Tatra 77]], one of the first streamlined cars with RR platform
File:VolkswagenBeetle-001.jpg|[[Engineering:Volkswagen Beetle|Volkswagen Bug/Beetle (VW Type 1)]]
File:Käferkühlung.svg|Illustration of the Beetle's engine air cooling in a Volkswagen Bug/Beetle (VW Type 1)
File:1962 Volkswagen Beetle Engine (3564060578).jpg|1962 Volkswagen Beetle Engine
File:Vw 411 v sst.jpg|[[Engineering:Volkswagen Type 4|Volkswagen Type 4]]: Volkswagen 411, Volkswagen 412
File:1970 Volkswagen 1600 (Type 3) TL fastback sedan (2015-12-07) 01.jpg|[[Engineering:Volkswagen Type 3|Volkswagen Type 3]]
File:MarignyMay07KarmannGhiaFrontSide.jpg|[[Engineering:Volkswagen Karmann Ghia|Volkswagen Karmann Ghia]]
File:Tatra mit Ro80 im Hintergrund color corrected.jpg|[[Engineering:Tatra 603|Tatra 603]] with RR platform.
File:1967 Chevrolet Corvair Monza Front.JPG|[[Engineering:Chevrolet Corvair|Chevrolet Corvair]]
File:Porsche 911 S 2.4 Urmodell 1971-1973 0000 frontright 2010-03-27 A.jpg|[[Engineering:Porsche 911|Porsche 911]] with RR platform. Some current models are now all-wheel drive.
File:De Lorean DMC-12 01.jpg|[[Engineering:DMC DeLorean|DMC DeLorean]] with RR platform.
File:SkodaS110R.jpg|Škoda 110R Coupé with RR platform.
File:1970 Fiat, Dutch licence registration 14-74-NP, pic2.jpg|The original [[Engineering:Fiat 500|Fiat 500]] was rear-engined.
File:Contessa1300Coupe.jpg|[[Engineering:Hino Contessa|Hino Contessa]]
File:1990 Volkswagen Multivan (12881834245).jpg|[[Engineering:Volkswagen Type 2 (T3)|Volkswagen Type 2 (T3)]]
File:Wasserboxer.jpg|Volkswagen Wasserboxer four-cylinder rear engine in a Volkswagen Type 2 (T3)
File:Oettinger wbx6 engine.jpg|An Oettinger WBX6, aftermarket six-cylinder rear engine in a Volkswagen Type 2 (T3)
File:1962 Volkswagen Type 2 2-door utility (26928884264).jpg|[[Engineering:Volkswagen Type 2|Volkswagen Type 2]], Single-cab utility pickup
File:1964 Volkswagen T1 Transporter Kombi bus (6106456722).jpg|[[Engineering:Volkswagen Type 2|Volkswagen T1 Microbus]]
File:Beach buggy - Flickr - exfordy.jpg|The [[Engineering:Meyers Manx|Meyers Manx]], a dune buggy, with VW rear engine
File:Rebelbaja.JPG|[[Engineering:Baja Bug|Baja Bug]]-style modified Beetle
File:Porsche Turbo 76.jpg|Early US- [[Engineering:Porsche 930|Porsche 930]] with "Turbo Carrera" label
File:CTR2 Alois Ruf.jpg|A view of the [[Engineering:Ruf CTR|Ruf CTR]] engine bay of the CTR with Alois Ruf present near the car
File:RUF CTR Yellowbird engine room.jpg|Ruf CTR Yellowbird rear powerplant.
File:Smart Forfour 1.0 Edition 1 (W 453) – Frontansicht, 15. März 2015, Düsseldorf.jpg|[[Engineering:Smart Forfour#2|Second generation Smart Forfour]]
File:Vw 181 v sst.jpg|[[Engineering:Volkswagen 181|Volkswagen 181]] also called the Volkswagen Thing, Safari, Trekker, and Pescaccia
File:Hillman Imp (1968).jpg|[[Engineering:Hillman Imp|Hillman Imp]]
File:180512-Vespa400-01.jpg|[[Engineering:Vespa 400|Vespa 400]]
File:Saporoshez ZAZ 965 A.JPG|[[Engineering:ZAZ Zaporozhets|ZAZ Zaporozhets]]
File:ZAZ-965 engine bay.jpg|ZAZ Zaporozhets Engine
File:Renault Alpine A 110 (Sp).JPG|[[Engineering:Alpine A110|Alpine A110]]
File:1948 Tucker Torpedo 8511815871.jpg|[[Engineering:Tucker 48|Tucker 48]]
File:1973 Simca 1000 GL.JPG|[[Engineering:Simca 1000|Simca 1000]]
File:13-04-05-Skoda Museum Mladá Boleslav by RalfR-121.jpg|[[Engineering:Škoda 1000 MB|Škoda 1000 MB]]
File:4cvfront.JPG|[[Engineering:Renault 4CV|Renault 4CV]]
File:1960 Renault 4CV (16396903299).jpg|1960 Renault 4CV longitudinally-mounted rear engine (750&nbsp;cc)
File:1961 Mitsubishi 500 01.jpg|[[Engineering:Mitsubishi 500|Mitsubishi 500]]
File:NSU Prinz II (12506691224).jpg|[[Engineering:NSU Prinz|NSU Prinz]] 2
File:Tata Nano Yellow.jpg|[[Engineering:Tata Nano|Tata Nano]]
File:Tata Nano Engine.JPG|Tata Nano engine in trunk that is only accessible from inside as a cost reduction feature
File:BMW 600, p2.jpg|Front door open and side door in view on a [[Engineering:BMW 600|BMW 600]]
File:Porsche 356 C - Flickr - Alexandre Prévot (2) (cropped).jpg|[[Engineering:Porsche 356|Porsche 356]]
File:The Porsche 356 01.jpg|Porsche 356 engine layout shows VW ancestry
File:Solaris Urbino 12 engine.jpg|[[Engineering:Solaris Urbino|Solaris Urbino]] 12 bus rear engine
File:Nishitetsu bus 9641 engine room.jpg|Nishitetsu bus rear engine
File:Nishi-Nippon Railroad - 9876.JPG|Nishitetsu bus
File:Mitsubishi i 2.jpg|The engine of the [[Engineering:Mitsubishi i|Mitsubishi i]]
File:Volkswagen ID.3 at IAA 2019 IMG 0779.jpg|[[Engineering:Volkswagen ID.3|Volkswagen ID.3]]
</gallery>

== References ==
{{reflist}}

{{Automobile configuration}}

{{DEFAULTSORT:Rear-Engine, Rear-Wheel Drive Layout}}
[[Category:Car layouts]]

{{Sourceattribution|Rear-engine, rear-wheel-drive layout}}