MR layout
Encyclopedia
In automotive design
, a 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 heaviest component is near the center of the car, making the main component of its moment of inertia
relatively low). 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.
In modern racing cars, RMR is the usual configuration and is usually synonymous with "mid engine". Due to its favorable weight dynamics, this layout is heavily employed in Formula racing
cars (such as Formula One
). This configuration was also common in very small engined 1950s microcar
s, in which the engines did not take up much space. Because of successes in racing, the RMR platform has been popular for road-going sports cars despite the inherent challenges of design, maintenance and lack of cargo space.
, an Austrian engineer working at Daimler. The Benz Tropfenwagen was designed by Ferdinand Porsche
along with Willy Walb and Hans Nibel. It raced in 1923 and 1924 and was most successful in the Italian Grand Prix
in Monza
where it stood fourth. Later, Ferdinand Porsche used mid-engine design concept towards the Auto Union Grand Prix
cars of the 1930s which became the first winning RMR racers. They were decades before their time, although MR Miller Specials raced a few times at Indianapolis
between 1939 and 1947. In 1953 Porsche
premiered the tiny and altogether new RMR 550 Spyder
and in a year it was notoriously winning in the smaller sports and endurance race car classes against much larger cars—a sign of greater things to come. The 718
followed similarly in 1958. But it was not until the late 1950s that RMR reappeared in Grand Prix (today's "Formula One
") races in the form of the Cooper
-Climax
(1957), soon followed by cars from BRM and Lotus
. Ferrari
and Porsche
soon made Grand Prix RMR attempts with less initial success. The mid-engined layout was brought back to Indianapolis
in 1961 by the Cooper Car Company
with Jack Brabham
running as high as third and finishing ninth. Cooper did not return, but from 1963 on British built mid-engined cars from constructors like Brabham, Lotus
and Lola competed regularly and in 1965 Lotus won Indy with their Type 38
.
Automotive design
Automotive design is the profession involved in the development of the appearance, and to some extent the ergonomics, of motor vehicles or more specifically road vehicles. This most commonly refers to automobiles but also refers to motorcycles, trucks, buses, coaches, and vans...
, a RMR or Rear Mid-engine
Mid-engine design
A mid-engine layout describes the placement of an automobile engine between the rear and front axles. Another term for this is mid-ship.-Benefits:The mid-engine layout is typically chosen for its relatively favorable weight distribution...
, 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
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
of the engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
is in front of the rear axle. This layout is typically chosen for its low moment of inertia
Moment of inertia
In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...
and relatively favorable weight distribution
Weight distribution
Weight distribution is the apportioning of weight within a vehicle, especially cars, airplanes, and trains.In a vehicle which relies on gravity in some way, weight distribution directly affects a variety of vehicle characteristics, including handling, acceleration, traction, and component life...
(the heaviest component is near the center of the car, making the main component of its moment of inertia
Moment of inertia
In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...
relatively low). 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.
In modern racing cars, RMR is the usual configuration and is usually synonymous with "mid engine". Due to its favorable weight dynamics, this layout is heavily employed in Formula racing
Formula racing
Formula racing is a term that refers to various forms of open wheeled single seater motorsport. Its origin lies in the nomenclature that was adopted by the FIA for all of its post-World War II single seater regulations, or formulae. The best known of these formulæ are Formula One, Formula Two, and...
cars (such as Formula One
Formula One
Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...
). This configuration was also common in very small engined 1950s microcar
Microcar
A microcar is the smallest automobile classification usually applied to standard small car . Such small cars were generally referred to as cyclecars until the 1940s. More recent models are also called bubblecars due to their egg-shaped appearance.-Definition:The definition of a microcar has varied...
s, in which the engines did not take up much space. Because of successes in racing, the RMR platform has been popular for road-going sports cars despite the inherent challenges of design, maintenance and lack of cargo space.
History
The 1923 Benz Tropfenwagen was the first race car with mid-engine, rear-wheel drive layout. It was based on an earlier design named the Rumpler Tropfenwagen in 1921 made by Edmund von RumplerRumpler
The Rumpler Tropfenwagen was a car developed by Austrian engineer Edmund Rumpler.Rumpler, born in Vienna, was a designer of aircraft when on the 1921's Berlin car show he introduced the Tropfenwagen. It was to be the first streamlined car . The Rumpler had a Cw-value of only 0.28...
, an Austrian engineer working at Daimler. The Benz Tropfenwagen was designed by Ferdinand Porsche
Ferdinand Porsche
Ferdinand Porsche was an Austrian automotive engineer and honorary Doctor of Engineering. He is best known for creating the first hybrid vehicle , the Volkswagen Beetle, and the Mercedes-Benz SS/SSK, as well as the first of many Porsche automobiles...
along with Willy Walb and Hans Nibel. It raced in 1923 and 1924 and was most successful in the Italian Grand Prix
Italian Grand Prix
The Italian Grand Prix is one of the longest running events on the motor racing calendar. The first Italian Grand Prix motor racing championship took place on 4 September 1921 at Brescia...
in Monza
Autodromo Nazionale Monza
The Autodromo Nazionale Monza is a race track located near the town of Monza, north of Milan, in Italy. The circuit's biggest event is the Formula One Italian Grand Prix, which has been hosted there since the sport's inception....
where it stood fourth. Later, Ferdinand Porsche used mid-engine design concept towards the Auto Union Grand Prix
Grand Prix motor racing
Grand Prix motor racing has its roots in organised automobile racing that began in France as far back as 1894. It quickly evolved from a simple road race from one town to the next, to endurance tests for car and driver...
cars of the 1930s which became the first winning RMR racers. They were decades before their time, although MR Miller Specials raced a few times at Indianapolis
Indianapolis 500
The Indianapolis 500-Mile Race, also known as the Indianapolis 500, the 500 Miles at Indianapolis, the Indy 500 or The 500, is an American automobile race, held annually, typically on the last weekend in May at the Indianapolis Motor Speedway in Speedway, Indiana...
between 1939 and 1947. In 1953 Porsche
Porsche
Porsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
premiered the tiny and altogether new RMR 550 Spyder
Porsche 550
The Porsche 550 was a sports car produced by Porsche from 1953-1956.Inspired by the Porsche 356 which was created by Ferry Porsche, and some spyder prototypes built and raced by Walter Glöckler starting in 1951, the factory decided to build a car designed for use in auto racing. The model Porsche...
and in a year it was notoriously winning in the smaller sports and endurance race car classes against much larger cars—a sign of greater things to come. The 718
Porsche 718
The Porsche 718 is an open-cockpit racing car build by Porsche between 1957 and 1962.The 718 was a development of the already successful 550A with improvements being made to the body work and suspension. The new front frame resembled the letter K if viewed from the front and this led to the car...
followed similarly in 1958. But it was not until the late 1950s that RMR reappeared in Grand Prix (today's "Formula One
Formula One
Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...
") races in the form of the Cooper
Cooper Car Company
The Cooper Car Company was founded in 1946 by Charles Cooper and his son John Cooper. Together with John's boyhood friend, Eric Brandon, they began by building racing cars in Charles' small garage in Surbiton, Surrey, England in 1946...
-Climax
Coventry Climax
Coventry Climax was a British forklift truck, fire pump, and speciality engine manufacturer.-History:The company was started in 1903 as Lee Stroyer, but two years later, following the departure of Stroyer, it was relocated to Paynes Lane, Coventry, and renamed to Coventry-Simplex by H...
(1957), soon followed by cars from BRM and Lotus
Lotus Cars
Lotus Cars is a British manufacturer of sports and racing cars based at the former site of RAF Hethel, a World War II airfield in Norfolk. The company designs and builds race and production automobiles of light weight and fine handling characteristics...
. Ferrari
Ferrari
Ferrari S.p.A. is an Italian sports car manufacturer based in Maranello, Italy. Founded by Enzo Ferrari in 1929, as Scuderia Ferrari, the company sponsored drivers and manufactured race cars before moving into production of street-legal vehicles as Ferrari S.p.A. in 1947...
and Porsche
Porsche
Porsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
soon made Grand Prix RMR attempts with less initial success. The mid-engined layout was brought back to Indianapolis
Indianapolis 500
The Indianapolis 500-Mile Race, also known as the Indianapolis 500, the 500 Miles at Indianapolis, the Indy 500 or The 500, is an American automobile race, held annually, typically on the last weekend in May at the Indianapolis Motor Speedway in Speedway, Indiana...
in 1961 by the Cooper Car Company
Cooper Car Company
The Cooper Car Company was founded in 1946 by Charles Cooper and his son John Cooper. Together with John's boyhood friend, Eric Brandon, they began by building racing cars in Charles' small garage in Surbiton, Surrey, England in 1946...
with Jack Brabham
Jack Brabham
Sir John Arthur "Jack" Brabham, AO, OBE is an Australian former racing driver who was Formula One champion in , and . He was a founder of the Brabham racing team and race car constructor that bore his name....
running as high as third and finishing ninth. Cooper did not return, but from 1963 on British built mid-engined cars from constructors like Brabham, Lotus
Team Lotus
Team Lotus was the motorsport sister company of English sports car manufacturer Lotus Cars. The team ran cars in many motorsport series including Formula One, Formula Two, Formula Ford, Formula Junior, IndyCar and sports car racing...
and Lola competed regularly and in 1965 Lotus won Indy with their Type 38
Lotus 38
The Lotus 38 was the first mid-engined car to win the Indianapolis 500, in 1965, driven by the great Jim Clark. It was run by Lotus at Indianapolis from 1965 to 1967; a total of 8 were built, most for use by Lotus, but several were sold for use by other drivers, including A. J...
.