Kammback

See also:Fastback

Kammback on a 1969 Fiat 850 Coupe

AKammback—also known as aKamm tailorK-tail—is anautomotive styling featurewherein the rear of the car slopes downwards before being abruptly cut off with a vertical or near-vertical surface. A Kammback reduces aerodynamic drag, thus improving efficiency and reducing fuel consumption,while maintaining a practical shape for a vehicle.

The Kammback is named after GermanaerodynamicistWunibald Kammfor his work developing the design in the 1930s.

Some vehicles incorporate the kammback design based on aerodynamic principles, while some use a cut-off tail as a design or marketing feature.

Origins

1950Nash Airflyte

1952Borgward Hansa 2400

As the speed of cars increased during the 1920s and 1930s, designers observed and began to apply the principles ofautomotive aerodynamics.Asaerodynamic dragincreases, more energy, and thus more fuel, is required to propel the vehicle.

In 1922,Paul Jaraypatented a car based on a teardrop profile (i.e. with a rounded nose and long, tapered tail) to minimize the aerodynamic drag that is created at higher speeds.Thestreamlinervehicles of the mid 1930s—such as theTatra 77,Chrysler AirflowandLincoln-Zephyr—were designed according to these discoveries.

However, the long tail was not a practical shape for a car, so automotive designers sought other solutions. In 1935, German aircraft designerGeorg Hans Madelungshowed alternatives to minimize drag without a long tail.In 1936, a similar theory was applied to cars after Baron Reinhard Koenig-Fachsenfeld developed a smooth roofline shape with an abrupt end at a vertical surface, effective in achieving low amounts of drag similar to a streamlined body.He worked on an aerodynamic design for a bus, and Koenig-Fachsenfeld patented the idea.Koenig-Fachsenfeld worked withWunibald Kammat Stuttgart University, investigating vehicle shapes to "provide a good compromise between everyday utility (e.g. vehicle length and interior dimensions) and an attractive drag coefficient".In addition to aerodynamic efficiency, Kamm emphasized vehicle stability in his design,mathematically and empirically proving the effectiveness of the design.

In 1938, Kamm produced a prototype using a Kammback shape, based on aBMW 328.The Kammback, along with other aerodynamic modifications, gave the prototype a drag coefficient of 0.25.

The earliest mass-produced cars using Kammback principles were the 1949–1951Nash Airflytein the United States and the 1952–1955Borgward Hansa 2400in Europe.

Aerodynamic theory

The ideal shape to minimize drag is a "teardrop," a smoothairfoil-like shape, but it is not practical for road vehicles because of size constraints.However, researchers, including Kamm, found that abruptly cutting off the tail resulted in a minimal increase in drag.The reason for this is that a turbulentwake regionforms behind the vertical surface at the rear of the car. This wake region mimics the effect of the tapered tail in that air in the free stream does not enter this region (avoidingboundary layer separation); therefore, smooth airflow is maintained, minimizing drag.

Kamm's design is based on the tail being truncated at the point where thecross sectionarea is 50% of the car's maximum cross-section,which Kamm found represented a good compromise, as by that point the turbulence typical of flat-back vehicles had been mostly eliminated at typical speeds.

The Kammback presented a partial solution to the problem of aerodynamic lift, which was becoming severe assports car racingspeeds increased during the 1950s. The design paradigm of sloping the tail to reduce drag was carried to an extreme on cars such as theCunningham C-5R,resulting in an airfoil effect lifting the rear of the car at speed and so running the risk of instability or loss of control. The Kammback decreased the area of the lifting surface while creating a low-pressure zone underneath the tail.

Some studies showed that the addition of a rear spoiler to a Kammback design was not beneficial because the overall drag increased with the angles that were studied.

Usage

1964-1969Ford GT40

1974-1985Citroën CX

2000-2006Honda Insight

2009–2015Toyota Prius

2011Audi A7

In 1959, the Kammback came into use on full-body racing cars as an anti-lift measure, and within a few years would be used on virtually all such vehicles. The design had a resurgence in the early 2000s as a method to reduce fuel consumption inhybrid electric vehicles.

Several cars have been marketed as Kammbacks despite their profiles not adhering to the aerodynamic philosophy of a true Kammback. These models include the 1971–1977Chevrolet VegaKammback wagon,the 1981–1982AMC EagleKammback,theAMC AMX-GT,and thePontiac Firebird–based "Type K" concept cars.

Some models that are marketed as "coupes"—such asBMWandMercedes-BenzSUVslike theX6andGLC Coupé— "use a sort-of Kammback shape, though their tail ends have a few more lumps and bumps than a proper Kammback ought to have."

Cars that have had a Kammback include:

• 1940BMW 328"Mille Miglia"Kamm coupé
• 1952Cunningham C-4RK

+ 1958-1963 Lotus Elite

• 1961Ferrari 250 GT SWB Breadvan
• 1962–1964Ferrari 250 GTO
• 1963Aston Martin DP215
• 1963-1964Porsche 904Carrera GTS
• 1963-1967Alfa Romeo Giulia TZ
• 1963–1974Bizzarrini Iso Grifo
• 1964-1965Shelby Daytona
• 1964-1968Ferrari 275GTB
• 1965–1968Ford GT40
• 1965–1970Aston Martin DB6
• 1965–1996, 2005–presentMini Marcos
• 1966Porsche 906
• 1966-1970Unipower GT
• 1966-1974Saab SonettII and III
• 1967-1977Alfa Romeo Tipo 33
• 1968–1973Ferrari 365 GTB/4( "Daytona" )
• 1968–1976Ferrari Dino
• 1968-1978Lamborghini Espada
• 1969–1971Fiat 850Coupe and Sport Coupe
• 1970–1975Citroën SM
• 1970–1977Alfa Romeo Montreal
• 1970–1986Citroën GS
• 1970–1978Datsun 240Z, 260Z, 280Z
• 1971–1989Alfa Romeo Alfasud
• 1971–1973Ford MustangFastback
• 1972–1982Maserati Khamsin
• 1972-1984Alfa Romeo Alfetta
• 1974–1991Citroën CX
• 1983-1991Honda CR-X
• 1985-1995Autobianchi Y10/Lancia Y10
• 1986-2016Daewoo LeMans
• 1991–1998Mazda MX-3
• 1994–1998Mazda Familia Neo/323C
• 1999-2005Audi A2
• 2000–2006Honda Insight
• 2004–presentToyota Prius
• 2007-2015Renault Laguna III
• 2010–2014Honda Insight(2nd generation)
• 2010-2016Honda CR-Z
• 2010–presentAudi A7
• 2012-2022Hyundai Veloster
• 2017–2022Hyundai Ioniq
• 2018–2023Kia Stinger
• 2020–presentTesla Model Y
• 2020–presentFord Mustang Mach-E
• 2024–presentLi Mega
• 2024–presentAston Martin Valour

See also

• Fastback,a similar automotive styling feature
• Liftback,a type of tailgate that cars with a Kammback often use