A design that started in 1900 race cars, won Formula One in under two years and still defines modern open-wheel racing and many road sports cars.
The rear mid-engine layout keeps the engine directly behind the passenger seats and forward of the rear axle, which gives balanced weight and resistance to understeer. Its roots lie in race cars of 1900, and it spread widely after the Second World War.
The engine sits just behind the passenger compartment, ahead of the rear axle, in a design that drives the rear wheels. Engineers often shorten it to RMR, and it now dominates open-wheel racing and many road sports cars. Its roots reach back to 1900, when a few purpose-built race cars first placed the engine there.
What is a rear mid-engine, rear-wheel-drive layout?
A rear mid-engine, rear-wheel-drive layout puts the engine in front of the rear axle, right behind the passenger compartment, with the rear wheels doing the driving. The term RMR is now preferred because some front-engine performance cars are also called mid-engine. Until the early 1990s these cars were usually just called MR.
The alternative is a rear-engine layout, in which the engine sits behind the rear axle. Mid-engine designs place the heaviest part inside the wheelbase, and that changes the way the car turns and holds the road.
The engine behind the driver gave racers traction, balance and a handling advantage that took Formula One within two years.
Why do designers choose it?
Designers choose the layout for its weight distribution. A near 50/50 split with a slight rear bias gives balanced braking and traction, and placing the heaviest component inside the wheelbase cuts the car's yaw inertia, which helps it turn in. The layout also tends to resist understeer, so the car pushes wide less often.
The trade-offs are real. With less weight over the front wheels, the front can lift under acceleration and still understeer. The engine also takes up the centre of the car, which leaves room for only one row of seats in most sports cars, with a handful of 2+2 designs as exceptions.
Rear-engine layouts, by contrast, have historically suited smaller vehicles. In a larger car the weight of an engine behind the rear axle makes it tail heavy. Some microtrucks use a mid-engine arrangement to move the cab forward, with a small low engine beneath a flat load floor.
How did the layout first appear?
The earliest examples date to 1900. The 1900 NW Rennzweier, built for Baron Theodor von Liebig with a flat-twin Benz engine, was one of the first purpose-built race cars with this layout. Engineer Edmund Rumpler, who also worked at Daimler and in aviation, built the Tropfenwagen in 1921, using a central driver seat and a rear mid-engine to reach a drag coefficient of 0.28.
The Tropfenwagen was a teardrop-shaped passenger car built in Berlin. It was no commercial success, although it was frequently used as a taxi. Carl Benz and Soehne licensed the design in 1922, but the tall curved windscreen proved impractical, so the work moved to open-top cars. The Benz Tropfenwagen race car, designed under Hans Nibel in 1923, followed, and Daimler and Benz merged in 1926.
Between the wars the mid-engine layout showed its traction advantages. Three Benz RH cars raced the 1923 Italian Grand Prix at Monza, and mid-engine cars won hillclimbs in 1924 and 1925. Porsche's P-Wagen concept, shaped for the 1934 Grand Prix rules, was adopted for the Auto Union racing cars. Adolf Rosenberger, a mid-engine hillclimb winner, later became Porsche's business partner when he set up an engineering bureau in Stuttgart.
| Milestone | Year | Detail |
|---|---|---|
| NW Rennzweier | 1900 | Flat-twin Benz engine behind the driver |
| Tropfenwagen | 1921 | Drag coefficient of 0.28 |
| Benz Tropfenwagen race car | 1923 | Designed under Hans Nibel |
| Auto Union | 1936 | Won every event in the European Championship season |
| Bugatti Type 251 | 1956 | First mid-engine single seater in Formula One |
| Mid-engine revolution | 1958 to 1959 | Formula One converts from front-engine cars |
Auto Union became the first Grand Prix winning RMR racers, but its cars were difficult to drive. Bernd Rosemeyer won the title in the supercharged V16 Typ C, and Mercedes developed new types and dominated the seasons that followed.
How did mid-engine cars take over Formula One?
The change in Formula One was rapid. Between early 1958 and June 1959, mid-engined cars displaced front-engined machinery, led by Cooper cars with Climax engines. Jack Brabham won the 1959 Monaco Grand Prix in a Cooper and defended his championship lead to the end of the season.
The 1956 French Grand Prix saw the Bugatti Type 251, the first rear mid-engine single seater in Formula One, although it was uncompetitive. In 1957 Formula Two cars of 1500cc were allowed in the German Grand Prix, and Cooper-Climax cars arrived there alongside Porsche 550 sports cars modified into single seaters.
The last front-engine win on a twisty circuit came at the Dutch Grand Prix on 31 May 1959, when Joakim Bonnier won in a BRM P25. Ferrari still won three more races, all on high-speed circuits. At the 1960 Italian Grand Prix the local organisers chose the banked oval version of Monza to help Ferrari.
By 1961 Lotus and BRM had adopted the Cooper-Climax layout, and the revolution was complete. Sports car racing took longer. Porsche's 550 won many class victories, including at the 1954 Carrera Panamericana, and the 718 won the 1959 Targa Florio. Porsche also won the 1960 Sebring 12 Hours. The 1956 Targa Florio gave a mid-engine race car its first major overall win since the 1930s, although that event was not then part of the World Sportscar Championship.
What happened in sports car racing and at Le Mans?
Sports car racing moved more slowly. Ferrari adopted the mid-engine layout for its 1961 SP series with a Dino V6. With a 2.4-litre engine and good handling, that car won the 1961 Targa Florio over the Porsche, and it won again in 1962. The 250P went on to win Sebring, the 1000 km Nurburgring and Le Mans in 1963. Ford's GT40 and Lola's cars followed with big US V8s behind the driver.
Porsche had to wait until the 917K won Le Mans overall in 1970, and the turbocharged 917/10 won Can-Am races in 1972. Oval racing was the last pure circuit series to adopt the layout. Cooper ran third at the 1961 Indianapolis 500 and finished ninth, and British cars from Brabham, Lotus and Lola competed regularly from 1963. The Lotus 38-Ford of Jim Clark won in 1965, followed by Graham Hill's Lola in 1966.
Other classes kept the rear-engined Porsche 911. It won the 1973 Targa Florio and Daytona, and the turbocharged 935 won Le Mans overall in 1979. In GT racing, balance of performance keeps different layouts competitive.
How did road cars adopt the layout?
Road cars followed more slowly. The very first Porsche 356/1 was mid-engined, but the regular production 356 used a rear-engine 2+2 layout to be useful as an everyday car. The Mercedes-Benz 150H had a mid-engine layout in the 1930s to improve handling in sport events, but it had no usable trunk and sold in low numbers. Microcars such as the Isetta used the arrangement widely in the 1950s, when the Zundapp Janus was also almost symmetric.
Porsche introduced the 550 in 1953 as a mid-engine two-seat sports car. It was mainly intended for competition, but it was also road legal, and customers drove it to events. Porsche sold about 300 road-racers until 1966, compared with about 77k of the 356. The VW-Porsche 914 followed from 1969, with a four-cylinder VW engine in the 914/4 and a Porsche flat-6 in the 914/6.
The first mid-engined road car sold after the Second World War was the 1962 Bonnet Matra Djet, which used a 1108cc Renault engine. Nearly 1700 were built before 1967. The De Tomaso Vallelunga, introduced at Turin in 1963, was followed by 58 cars built over the following few years.
Larger mid-engine road cars arrived in the 1960s. The Italian ATS 2500 GT V8 appeared in 1963, and the Lamborghini Miura of 1966 was the first high-performance V12 mid-engine rear-wheel-drive road car. Its 4-litre V12 sat transversely between the rear wheels. Most competitors, from Ferraris and Maseratis to Jaguars and Aston Martins, were front-engined grand tourers.
The Pontiac Fiero, built from 1984 to 1988, was the first two-seater Pontiac since the 1926 to 1938 coupes, and the first mass-produced mid-engine sports car by a US manufacturer.
Which layouts did engineers use?
Engineers split the layout into transverse and longitudinal versions. Early cars such as the Miura used a transverse mounting, with the crankshaft parallel to the axle, while later supercars such as the Countach used a longitudinal engine ahead of the axle. Small sports cars often borrow heavily from front-wheel-drive designs.
The transverse arrangement is still common in smaller sports cars such as the Toyota MR2 and the Alfa Romeo 4C. It is compact and cuts development and component costs, which suits companies that buy engines from others, such as Lotus with its Elise.
Longitudinal designs often share engines with front-engined, rear-wheel-drive cars, as with the LaFerrari and the Pagani Zonda. A few mid-engined 2+2s appeared as well. The Ferrari Dino 308 GT4 and Mondial used transverse engines to make room for rear seats, as did the Lamborghini Urraco, and the Lotus Evora later kept the concept with a V6. The Maserati Merak fitted a longitudinal V6 into a 2+2.
What are the advantages and drawbacks of the layout?
The layout's main advantages are balanced weight, low yaw inertia and resistance to understeer, which suit racing and fast road driving. Its drawbacks are lost space for passengers and luggage, harder maintenance and a tendency for the front to lighten under power.
Racing teams have adopted the layout widely in open-wheel formulae and purpose-built sports racers, and success in motorsport has carried it into road cars. Four-wheel-drive mid-engine variants add traction where it is needed, as in some supercars and in Group B rally cars.
The drawbacks are practical. The engine takes space that could carry passengers, so most mid-engined cars have a single row of seats. Cargo room suffers, and maintenance is harder because the engine sits deep in the car.
