Automobile drag coefficient

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The drag coefficient is a common metric in automotive design, where designers strive to achieve a low coefficient. Minimizing drag is done to improve fuel efficiency at highway speeds, where aerodynamic effects represent a substantial fraction of the energy needed to keep the car moving. Indeed, aerodynamic drag increases as the square of speed. Aerodynamics are also of increasing concern to truck designers, where a lower drag coefficient translates directly into lower fuel costs.

About 60% of the power required to cruise at highway speeds is taken up overcoming air drag, and this increases very quickly at high speed. Therefore, a vehicle with substantially better aerodynamics will be much more fuel efficient.

[edit] Drag in sports and racing cars

Reducing drag is also a factor in sports car design, where fuel efficiency is less of a factor, but where low drag helps a car achieve a high top speed. However, there are other important aspects of aerodynamics that affect cars designed for high speed, including racing cars. Notably, it is important to minimize lift, hence increasing downforce, to avoid the car ever becoming airborne and instead force the car onto the track -- allowing higher cornering speed for the vehicle. Also it is important to maximize aerodynamic stability: some racing cars have tested well at particular "attack angles", yet performed catastrophically, i.e. flipping over, when hitting a bump or experiencing turbulence from other vehicles (most notably the Mercedes-Benz CLR). For best cornering and racing performance, as required in Formula 1 cars, downforce and stability are crucial and these cars must attempt to maximize downforce and maintain stability while attempting to minimize the overall C_d value.

[edit] Typical values and examples

The average modern automobile achieves a drag coefficient of between 0.30 and 0.35. SUVs, with their typically boxy shapes and larger frontal area, typically achieve a Cd of 0.35–0.45. A very gently inclined windshield gives a lower drag coefficient but has safety disadvantages, including reduced driver visibility. Certain cars can achieve figures of 0.25–0.30, although sometimes designers deliberately increase drag in order to reduce lift.

Some examples of C_d follow. Figures given are generally for the basic model. Some "high performance" models may actually have higher drag, due to wider tires and extra spoilers.

Production cars
C_d	Automobile	Year
0.7 to 1.1	typical values for a Formula 1 car (downforce settings change for each circuit)
0.74	Legends Car
0.7	Caterham Seven
0.6 +	a typical truck
0.57	Hummer H2	2003
0.51	Citroën 2CV	1948
0.48	Volkswagen Beetle (newer models) ^[1] ^[2]
0.47	Lancia Aprilia	1937
0.46	Ford Mustang (coupe)	1979
0.45	Dodge Viper RT/10	1996
0.44	Ford Mustang (fastback)	1979
0.44	Peugeot 305	1978
0.44	Peugeot 504	1968
0.44	Toyota Truck	1990
0.425	Duple 425 coach (named for its low C_d by coach standards)	c.1985
0.42	Lamborghini Countach	1974
0.42	Triumph Spitfire Mk IV	1971
0.42	Plymouth Duster	1994
0.41	Volvo 740 (sedan)	1982
0.40	Ford Escape Hybrid	2005
0.40	Nissan Skyline GT-R R32	1989
0.39	Dodge Durango	2004
0.39	Chevrolet Tahoe	2006
0.39	Triumph Spitfire	1964
0.38	Volkswagen Beetle (original design)^[3]	1938
0.38	VW NewBeetle^[4] without wing or spoiler 0.39^[5]	2003
0.385	Nissan 280ZX	1978
0.38	Mazda Miata	1989
0.374	Ford Capri Mk III	1978
0.372	Ferrari F50	1996
0.37	Renault Twingo
0.37	BMW Z3 M coupe	1999
0.37	Volkswagen Tiguan	2008
0.36	Cadillac Escalade hybrid	2008
0.36	Cadillac Fleetwood	1996
0.36	Citroën CX (named after the term for C_d)	1974
0.36	Citroën DS	1955
0.36	Chrysler Sebring	1996
0.36	Ferrari Testarossa	1986
0.36	Ford Mustang	1999
0.36	Honda Civic	2001
0.36	Opel GT	1969
0.355	NSU Ro 80	1967
0.35	Aston Martin Vanquish	2004
0.35	BMW Z4 M coupe	2006
0.35	Dodge Viper GTS	1996
0.35	Jaguar XKR	2005
0.35	Lexus RX	2003-2009
0.35	MINI Cooper	2008
0.35	Tesla Roadster^[6]	2008
0.35	Toyota MR-2	1998
0.35	Toyota Sequoia	2007
0.35	Volvo 940 (sedan)	1990
0.35	SSC Ultimate Aero	2007-Present
0.34	Aston Martin DB9	2004
0.34	Chevrolet Caprice	1994
0.34	Chevrolet Tahoe hybrid	2008
0.34	Ferrari F40	1987
0.34	Ferrari 360 Modena	1999
0.34	Ferrari F430 F1	2004
0.34	Ford Sierra	1982
0.34	Ford Puma	1997
0.34	Honda Prelude	1988
0.34	Mercedes-Benz SL (Roof Down)	2001
0.34	Peugeot 106	1991
0.34	Toyota Supra (with factory 3 piece turbo wing)	1989-1990
0.338	Chevrolet Camaro	1995
0.33	Audi A3	2006
0.33	Citroën SM	1970
0.33	Dodge Charger	2006
0.33	Ford Crown Victoria	1992
0.33	Honda Accord Sedan	2002
0.33	Lamborghini Murcielago	2001
0.33	Lexus RX	2009
0.33	Mazda RX-7 FC3C	1987
0.33	Peugeot 206	1998
0.33	Peugeot 309	1986
0.33	Renault Modus	2004
0.33	Subaru Impreza WRX STi	2004
0.33	Toyota Supra (without wing)	1989-1990
0.324	Cobalt SS Supercharged	2005
0.32	AMC Pacer	1975-1980
0.32	Buick Riviera	1995
0.32	Dodge Avenger	1995
0.32	Honda Accord Coupe	2002
0.32	Honda NSX	1990
0.32	Mazdaspeed3	2007
0.32	McLaren F1	1992
0.32	Mercedes-Benz 190E 2.5-16/2.3-16
0.32	Nissan 300ZX	1989
0.32	Nissan Maxima	1997
0.32	Porsche 997 GT2
0.32	Peugeot 406	1995
0.32	Peugeot 806	1994
0.32	Scion xB	2008
0.32	Suzuki Swift	1991
0.32	Toyota Celica	1994
0.32	Toyota Supra (N/A with wing and turbo models)	1993
0.32	Toyota Supra (with factory turbo wing)	1987-1988
0.32	Volkswagen GTI Mk V	2006
0.31	Audi A4 B5	1995
0.31	BMW 7-series	2009
0.31	Buick Park Avenue	1996
0.31	Cadillac CTS-V	2005
0.31	Chevrolet C6 Corvette Z06
0.31	Citroën AX	1986
0.31	Citroën GS	1970
0.31	Eagle Vision	1995
0.31	Ford Falcon	1995
0.31	Holden Commodore	1998
0.31	Honda Civic (Sedan)	2006
0.310	Lamborghini Diablo	1990
0.31	Mazda RX-7 FC3S	1986
0.31	Mazda RX-7 FD R1(R2)	1993
0.31	Mazda RX-8	2004
0.31	Nissan Tiida / Versa	2004
0.31	Peugeot 307	2001
0.31	Porsche 997 Turbo/GT3	2006
0.31	Renault 25	1984
0.31	Saab Sonett III	1970
0.31	Scion xA	2004
0.31	Toyota Avalon	1995-2000
0.31	Toyota RAV4	2006
0.31	Toyota Supra (N/A; without factory wing)	1993
0.31	Volkswagen GTI Mk IV	1997
0.30	Honda NSX	2002
0.30	Audi 100	1983
0.30	BMW E90	2006
0.30	Hyundai Sonata	2006
0.30	Honda Accord Sedan	2003, 2005-2007
0.30	Honda Odyssey	2005
0.30	Koenigsegg CCX	2006
0.30	Mitsubishi Eclipse	2000
0.30	Nissan 180SX	1989
0.30	Nissan 300ZX	1983
0.30	Nissan 350Z Coupe Base and Enthusiast models	2003-2008
0.30	Nissan 370Z Coupe (0.29 with sport package)	2008
0.30	Renault 19 16V	1991
0.30	Saab 92	1947
0.30	Toyota Sienna	2003-2009
0.295	Ford Falcon	1998
0.29	Alfa Romeo 155	1992
0.29	BMW 8-Series	1989
0.29	Chevrolet Corvette	2005
0.29	Chevrolet Corvette C5 Z06	2002
0.29	Daewoo Espero	1990
0.29	Dodge Charger Daytona	1969
0.29	Eagle Talon	1990s [2]
0.29	Honda Accord Hybrid	2005, 2007
0.29	Honda Accord Coupe	2003, 2005-2007
0.29	Honda CRX HF	1988
0.29	Infiniti G35 Sedan	2008
0.29	Lancia Dedra	1990
0.29	Lexus LS 400	1990
0.29	Lotus Elite	1958
0.29	Lotus Europa	1966
0.29	Mazda Millenia	1995
0.29	Mazda RX-7 FC3S Aero Package	1986
0.29	Mazda 3	2010
0.29	Mazda RX-7 FD	1993
0.29	Mercedes-Benz SL (Roof Up)	2001
0.29	Mercedes-Benz W203 C-Class Coupe	2001
0.29	Nissan 350Z Coupe Track and Grand Touring	2007-2008
0.29	Nissan Versa	2007-2008
0.29	Peugeot 308	2007
0.29	Peugeot 407	2004
0.29	Peugeot 607	1999
0.29	Porsche Boxster	2005
0.29	Subaru XT	1985
0.29	Subaru SVX	1992
0.29	Toyota Camry	1996-2001
0.291	Toyota Avalon	2005
0.29	Toyota Prius	2001
0.286	Chevrolet Corvette C6	2006
0.28	Citroën XM	1989
0.28	Citroën C4	2004
0.28	Lexus IS	2006
0.28	Mitsubishi Diamante	1995
0.28	Porsche 997 Carrera (with optional automatic spoiler, PDK transmission 0.30)	2004
0.28	Renault 25 TS	1984
0.28	Rumpler-Tropfenwagen	1921
0.28	Saab 9-3	2003
0.28	Toyota Camry / Lexus ES	2001
0.28	Volkswagen NewBeetle with custom, hand-crafted wing^[7]	2003
0.28	Opel Astra Coupe Turbo	2003
0.27	Honda Civic Hybrid	2006
0.27	Hyundai Genesis	2009
0.27	Infiniti G35 (0.26 with "aero package")	2002
0.27	Lexus GS	2005
0.27	Mazda6 (sedan and hatchback) ^[8]	2008
0.27	Mercedes-Benz W203 C-Class Sedan	2001
0.27	Nissan GT-R	2008
0.27	Toyota Camry Hybrid	2007
0.27	Tucker Torpedo	1948
0.27	Volkswagen Passat B5 (sedan)	1997
0.27	Mercedes-Benz S Class (0.268 with Sport Package)	2000-2005
0.26	Hotchkiss Gregoire^{[citation needed]}	1951
0.26	Lexus LS 430 (0.25 with air suspension)	2001-2006
0.26	Lexus LS 460	2006
0.26	Mercedes-Benz W221 S-Class	2006
0.26	Opel Calibra (8 valve version)	1989
0.26	Toyota Prius	2004-2009
0.25	Audi A2 1.2 TDI	2001
0.25	Honda Insight	1999, 2003, 2005
0.25	Toyota Prius	2010
0.24	Mercedes E-class coupe (0.25 sedan)	2009
0.212	Tatra T77	1935
0.195	General Motors EV1	1996

Concept/experimental cars
C_d	Automobile	Year
0.301	Chevrolet Volt (0.43 w/ a 30% reduction)	2010
0.27	Avion^[9]	1986
0.26	Alfa Romeo Disco Volante	1952
0.25	Dymaxion Car	1933
0.25	SmILE (an experimental car)	1996
0.22	Citroën ECO 2000 Concept	1981^[10]
0.20	Loremo Concept	2006 2009 (Planned production)
0.20	Opel Eco Speedster Concept	2003
0.19	Alfa Romeo B.A.T. 7 Concept	1954
0.19	Dodge Intrepid ESX Concept	1995
0.19	Mercedes-Benz Bionic Concept^[11](based on the boxfish)	2005
0.168	Daihatsu UFE-III Concept	2005^[12]
0.16	General Motors Precept Concept (5 seats)	2000
0.159	Volkswagen 1-litre car Concept	2002 2010 (Planned production)
0.15	Aptera Motors 2e	2009 (Planned production)
0.14	Fiat Turbina Concept	1954
0.137	Ford Probe V Concept	1985
0.125	Sunraycer, solar race car	1987
0.12	Reflex 1000, solar cycle	1996^[13]
0.117	Summers Brothers Goldenrod Bonneville race car	1965
0.08	Fortis Saxonia (Shell Eco-marathon) Concept	2007
0.075	PAC-Car II (Shell Eco-marathon) Concept	2005
0.07	Nuna, World Solar Challenge winner	2001-2007

[edit] C_dA

While designers pay attention to the overall shape of the automobile, they also bear in mind that reducing the frontal area of the shape helps reduce the drag. The combination of drag coefficient and area is C_dA (or C_xA), a multiplication of the C_d value by the area.

In aerodynamics, the product of some reference area (such as cross-sectional area, total surface area, or similar) and the drag coefficient is called drag area. In 2003, Car and Driver adapted this metric and adopted it as a more intuitive way to compare the aerodynamic efficiency of various automobiles. Average full-size passenger cars have a drag area of roughly 8.5 ft² (.79 m²). Reported drag area ranges from the 1999 Honda Insight at 5.1 ft² (.47 m²) to the 2003 Hummer H2 at 26.3 ft² (2.44 m²). The drag area of a bicycle is also in the range of 6.5-7.5 ft².^[14]

Automobile examples of C_dA ft² are shown below: ^[15]

C_dA (ft²)	Automobile model
2.11	2009 Aptera 2 Series
2.50	1986 Twike ^[16]
3.95	1996 GM EV1
5.10	1999 Honda Insight
5.40	1989 Opel Calibra
5.71	1990 Honda CR-X Si
5.74	2002 Acura NSX
5.76	1968 Toyota 2000GT
5.80	1986 Toyota MR2
5.81	1989 Mitsubishi Eclipse GSX
5.86	2001 Audi A2 1.2 TDI 3L
5.88	1990 Nissan 240SX hatchback / 200SX / 180SX
5.92	1994 Porsche 911 Speedster
5.95	1990 Mazda RX7
6.00	1970 Lamborghini Miura
6.08	2008 Nissan GTR
6.13	1991 Acura NSX
6.17	1995 Lamborghini Diablo
6.24	2004 Toyota Prius
6.27	1986 Porsche 911 Carrera
6.27	1992 Chevrolet Corvette
6.35	1999 Lotus Elise
6.40	1990 Lotus Esprit
6.54	1991 Saturn Sports Coupe
6.57	1985 Chevrolet Corvette
6.63	2001 Audi A2
6.66	1996 Citroën Saxo
6.77	1995 BMW M3
6.79	1993 Toyota Corolla DX
6.81	1991 Subaru Legacy
6.90	1993 Saturn Wagon
6.93	1982 Delorean DMC-12
6.96	1988 Porsche 944 S
6.96	1995 Chevrolet Lumina LS
7.02	1992 BMW 325I
7.04	1991 Honda Civic EX
7.10	1995 Saab 900
7.14	1995 Subaru Legacy L
7.34	2001 Honda Civic
7.39	1994 Honda Accord EX
7.48	1993 Chevrolet Camaro Z28
7.57	1992 Toyota Camry
7.69	1994 Chrysler LHS
7.72	1993 Subaru Impreza
8.02	2005 Bugatti Veyron
8.70	1990 Volvo 740 Turbo
8.70	1992 Ford Crown Victoria
8.71	1991 Buick LeSabre Limited
9.54	1992 Chevrolet Caprice Wagon
10.7	1992 Chevrolet Blazer
11.6	2005 Ford Escape Hybrid
11.7	1993 Jeep Grand Cherokee
16.8	2006 Hummer H3
17.4	1995 Land Rover Discovery
26.5	2003 Hummer H2

[edit] Selected photographs

2.1 - a smooth brick having twice drag coefficient twice a flat edgy plate seems to be the ideal parachute shape	0.7 to 1.1 - typical values for a Formula 1 car	0.9 -a typical bicycle plus cyclist	0.7 - Caterham Seven	at least 0.6 - a typical truck
0.57 - Hummer H2, 2003	0.51 - Citroën 2CV due to the mudguard, despite the round roof	0.48 - Volkswagen Beetle due to vertical headlights, wider tires and mudguard	0.425 - Duple 425 coach	0.42 - Lamborghini Countach, 1974
0.42 - Triumph Spitfire Mk IV, 1971-1980	0.38 - Volkswagen Beetle original design	0.38 - Mazda Miata, 1989	0.38 - Rolls-Royce Silver Seraph, 1998 [1]	0.374 - Ford Capri Mk III, 1978-1986
0.372 - Ferrari F50, 1996 high drag due to aerodynamic aids and cooling ducts.	0.36 - Citroën DS, 1955, relative high drag despite the aerodynamic headlights, due to the rough windshield-roof transition.	0.36 - Ferrari Testarossa, 1986	0.36 - Honda Civic, 2001	0.36 - Citroën CX, 1974 (the car was named after the term for drag coefficient)
0.355 - NSU Ro 80, 1967 despite the edgy front	0.35, Audi TT, 1998 [2] much drag despite smooth shape, the similar 2007 version has 0.30 [3]	0.35 - Dodge Viper GTS	0.342 Pontiac Trans Am 1982 [4]	0.34 - Ford Sierra, 1982, at least one combi in this gallery! The passat 2003, has 0.32
0.34 - Ferrari F40, 1987	0.338 - Chevrolet Camaro, 1995	0.33 - Citroën SM, 1970 low drag despite edgy front	0.32 - Buick Riviera, 1995	0.31 - Citroën AX, 1986 low drag due to down pulled hood
0.31 - Citroën GS, 1970	0.31 - Renault 25, 1984	0.31 - Saab Sonett III, 1970	0.30 - Audi 100, 1983 smooth nose to flow transition	0.30 - BMW E90, 2006
0.30 - Porsche 996, 1997	0.30 - Saab 92, 1947 - developed using wind tunnel testing	0.29 - Honda CRX HF 1988	0.29 - Subaru XT, 1985	0.29 - Lancia Dedra, 1990-1998
0.29 - Lotus Elite, 1958	0.28 - Rumpler Tropfenwagen, 1921 thin tires have low aerodynamic drag	0.28 - Toyota Camry and sister model Lexus ES, 2005	0.28 - Porsche 997, 2004, and that with the wide tires	0.28 - Renault 25 TS, 1984, low drag despite its overall edgy shape
0.28 - Saab 9-3, 2003	0.28 - Audi A2, 1999 [5]. Note the Kammback shape.	0.28 - Chevrolet Corvette Z06, 2006	0.27 - Infiniti G35, 2002 (0.26 with "aero package")	0.27 - Toyota Camry Hybrid, 2007
0.26 - Mercedes-Benz W221 S-Class, 2006, low drag despite wheelarches an a large grill and a Mercedes sign in the airflow	0.26 - Lexus LS 430, 2001 (0.25 with air suspension)	0.26 - Toyota Prius, 2004	0.26 - Vauxhall Calibra, 1989 even the transition from the bumpers to the head light is smooth	0.25 - Audi A2 1.2 TDI, 2001, low drag despite wheelarches, due to down pulled hood and fastback
0.25 - Honda Insight, 1999, low drag due to down pulled hood,fastback and wheel fairings	0.212 - Tatra T77 a, 1935, low drag due to a tail and a smooth underbody and despite an edgy windscreen-roof transition.	0.195 - General Motors EV1 (electric), 1996, low drag due to having wheel fairings, relative central head lights, submerged wiper	0.15 - Aptera Motors Typ-1 (2008 planned) having a tail, wheel fairings, smooth underbody, aerodynamic suspension