In automotive design, an 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, the center of mass of the engine is between the rear axle and the rear bumper. Although very common in transit buses and coaches due to the elimination of the drive shaft with low-floor buses, this layout has become increasingly rare[ specify ] in passenger cars.
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 differential can be integrated with the transmission, commonly referred to as a 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 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 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.
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 Volkswagen Beetle, and one of the few production air-cooled turbocharged cars, the 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 liquid-cooled engines in modern cars, most manufacturers have abandoned the RR layout. The major exception is Porsche, who has developed the 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.
One of first RR cars was Tatra 77 of 1934, the first serial-produced aerodynamic car, designed by Hans Ledwinka. Tatra used this layout until end of production of T700 in 1999. In case of T613 and 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 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' (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 Type 3 of 1961, which flattened the engine (or 'pancake'), allowing for luggage spaces front and rear.
Porsche has continued to develop its 911 model as a rear-engined vehicle, although they have introduced multiple all-wheel-drive models. Most notably, the 911 Turbo has been sold as AWD-only since the release of the 993 model. Race-oriented models such as the GT3 and twin-turbocharged GT2 remain solely RR, however.
Another manufacturer to implement the RR configuration was the DeLorean Motor Company with its 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 composite materials 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, Volkswagen Beetle, Porsche 356, Chevrolet Corvair, NSU Prinz and Hino Contessa.
Many modern electric cars such as the Mitsubishi i-MiEV, BMW i3, Volkswagen ID.3, Smart Forfour and Tesla Model 3 (Rear-Wheel-Drive version only) use an RR layout due to the low weight and cooling requirements of the electric motor. The Tesla Cybertruck and GMC Hummer EV will also use this layout for their base variants.
Most modern heavy duty buses use an extreme RR layout. In transit buses 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.
The Tata Nano, the cheapest ($2100 - $2500) production car in the world introduced in 2008 and built in India, also features this layout.
The Volkswagen Beetle—officially the Volkswagen Type 1, informally in German der Käfer, in parts of the English-speaking world the Bug, and known by many other nicknames in other languages—is a two-door, rear-engine economy car, intended for five occupants, that was manufactured and marketed by German automaker Volkswagen (VW) from 1938 until 2003.
A flat engine, also known as a horizontally opposed engine, is a piston engine where the cylinders are located on either side of a central crankshaft. A flat engine should not be confused with the opposed-piston engine, in which each cylinder has two pistons sharing a central combustion chamber.
The Chevrolet Corvair is a compact car manufactured by Chevrolet for model years 1960–1969 in two generations. It remains the only American-designed, mass-produced passenger car with a rear-mounted, air-cooled engine. The Corvair was manufactured and marketed in 4-door sedan, 2-door coupe, convertible, 4-door station wagon, passenger van, commercial van, and pickup truck body styles in its first generation (1960–1964) and as a 2-door coupe, convertible or 4-door hardtop in its second (1965–1969) — with a total production of approximately 1.8 million from 1960-1969.
A torsion bar suspension, also known as a torsion spring suspension, is any vehicle suspension that uses a torsion bar as its main weight-bearing spring. One end of a long metal bar is attached firmly to the vehicle chassis; the opposite end terminates in a lever, the torsion key, mounted perpendicular to the bar, that is attached to a suspension arm, a spindle, or the axle. Vertical motion of the wheel causes the bar to twist around its axis and is resisted by the bar's torsion resistance. The effective spring rate of the bar is determined by its length, cross section, shape, material, and manufacturing process.
quattro is the sub-brand used by the car brand Audi to indicate that all-wheel drive (AWD) technologies or systems are used on specific models of its Audi automobiles.
Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.
The Volkswagen Type 3 is a compact car that was manufactured and marketed by Volkswagen from 1961 to 1973. Introduced at the 1961 Frankfurt Motor Show, Internationale Automobil-Ausstellung (IAA), the Type 3 was marketed as the Volkswagen 1500 and later as the Volkswagen 1600, in three body styles: two-door Notchback, Fastback and Variant, the latter marketed as the 'Squareback' in the United States.
In automotive design, an FF, or front-engine, front-wheel-drive (FWD) layout places both the internal combustion engine and driven roadwheels at the front of the vehicle.
In automotive design, an 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. This layout is typically chosen for its low moment of inertia and relatively favorable weight distribution. The layout has a tendency toward being heavier in the rear than the front, which allows for best balance to be achieved under braking. However, since there is little weight over the front wheels, under acceleration, the front of the car is prone to lift and cause understeer. Most rear-engine layouts have historically been used in smaller vehicles, because the weight of the engine at the rear has an adverse effect on a larger car's handling, making it 'tail-heavy'. It is felt that the low polar inertia is crucial in selection of this layout. The mid-engined layout also uses up central space, making it impractical for any but two-seater sports cars. However, some microvans use this layout, with a small, low engine beneath the loading area. This makes it possible to move the driver right to the front of the vehicle, thus increasing the loading area at the expense of slightly reduced load depth.
Economy car is a term mostly used in the United States for cars designed for low-cost purchase and operation. Typical economy cars are small, lightweight, and inexpensive to both produce and purchase. Stringent design constraints generally force economy car manufactures to be inventive. Many innovations in automobile design were originally developed for economy cars, such as the Ford Model T and the Austin Mini.
Rear-wheel drive (RWD) is a form of engine and transmission layout used in motor vehicles, where the engine drives the rear wheels only. Until the late 20th century, rear-wheel drive was the most common configuration for cars. Most rear-wheel drive vehicles feature a longitudinally-mounted engine at the front of the car.
A transaxle is a single mechanical device which combines the functions of an automobile's transmission, axle, and differential into one integrated assembly. It can be produced in both manual and automatic versions.
A mid-engine layout describes the placement of an automobile engine in front of the rear-wheel axles, but behind the front axle.
A swing axle is a simple type of independent suspension designed and patented by Edmund Rumpler in 1903. This was a revolutionary invention in the automotive industry, allowing wheels to react to irregularities of road surfaces independently, and enable the vehicle to maintain a strong road holding. The first automotive application was the Rumpler Tropfenwagen, later followed by the Mercedes 130H/150H/170H, the Standard Superior, the Volkswagen Beetle and its derivatives, and the Chevrolet Corvair, amongst others.
In automobile design, a rear-engine design layout places the engine at the rear of the vehicle. The center of gravity of the engine itself is behind the rear axle. This is not to be confused with the center of gravity of the whole vehicle, as an imbalance of such proportions would make it impossible to keep the front wheels on the ground.
The layout of a motorised vehicle such as a car is often defined by the location of the engine and drive wheels.
Backbone tube chassis is a type of automobile construction chassis that is similar to the body-on-frame design. Instead of a two-dimensional ladder-type structure, it consists of a strong tubular backbone that connects the front and rear suspension attachment areas. A body is then placed on this structure. It was first used in the English Rover 8hp of 1904 and then the French Simplicia automobile in 1909.
Kelmark Engineering was an automotive specialty shop established in 1969 and based in Okemos, Michigan. It focused on high-performance custom V8 drivetrain swaps, the modification and production of rear and mid-engined cars, and custom-built turn-key automobiles. Until 1986, Kelmark Engineering manufactured kits and complete, finished, turn-key vehicles which were either Volkswagen-based or built on tubular race car-type frames. The outfit gained its name from Russ Keller and Randy Markham, the two co-creators who started the operation. Up until at least 1989, the Kelmark GT was still available as a kit albeit the manufacturer was Kelmark Motors in Holt, Michigan. The cars are all "rare" models, but the Volkswagen-powered Kelmark GT was the most popular.
In automotive design, an R4, or Rear-engine, Four-wheel-drive layout places the internal combustion engine at the rear of the vehicle, and drives all four roadwheels.
A platform chassis is a form of vehicle frame / automobile chassis, constructed as a flat plate or platform, sometimes integrating a backbone or frame-structure with a vehicle's floor-pan.