Automobile drag coefficient

Tatra 77 maquette by Paul Jaray, 1933. This vehicle was the first serial-produced truly aerodynamically designed automobile.

The drag coefficient is a common measure in automotive design as it pertains to aerodynamics. Drag is a force that acts parallel and in the same direction as the airflow. The drag coefficient of an automobile impacts the way the automobile passes through the surrounding air. When automobile companies design a new vehicle they take into consideration the automobile drag coefficient in addition to the other performance characteristics. Aerodynamic drag increases with the square of speed; therefore it becomes critically important at higher speeds. Reducing the drag coefficient in an automobile improves the performance of the vehicle as it pertains to speed and fuel efficiency.^[1] There are many different ways to reduce the drag of a vehicle. A common way to measure the drag of the vehicle is through the drag area.

Reducing drag

The reduction of drag in road vehicles has led to increases in the top speed of the vehicle and the vehicle's fuel efficiency, as well as many other performance characteristics, such as handling and acceleration.^[2] The two main factors that impact drag are the frontal area of the vehicle and the drag coefficient. The drag coefficient is a unit-less value that denotes how much an object resists movement through a fluid such as water or air. A potential complication of altering a vehicle's aerodynamics is that it may cause the vehicle to get too much lift. Lift is an aerodynamic force that flows perpendicular to the airflow around the body of the vehicle. Too much lift can cause the vehicle to lose road traction which can be very unsafe.^[3] Lowering the drag coefficient comes from streamlining the exterior body of the vehicle. Streamlining the body requires assumptions about the surrounding airspeed and characteristic use of the vehicle.

For high speed applications near or above the speed of sound, a Sears-Haack body,^[4][5] is an idealized shape that minimizes wave drag, which is the drag associated with supersonic shock waves. This shape essentially consists of an elongated tube with pointed ends.

Deletion

The deletion of parts on a vehicle is an easy way for designers and vehicle owners to reduce parasitic and frontal drag of the vehicle with little cost and effort. Deletion can be as simple as removing an aftermarket part, or part that has been installed on the vehicle after production, or having to modify and remove an OEM part, meaning any part of the vehicle that was originally manufactured on the vehicle. Most production sports cars and high efficiency vehicles come standard with many of these deletions in order to be competitive in the automotive and race market, while others choose to keep these drag-increasing aspects of the vehicle for their visual aspects, or to fit the typical uses of their customer base.^[6]

Roof rack

A roof rack is a common trait on many SUV and station wagon vehicles. While roof racks are very useful in carrying extra storage on a vehicle, they also increase the frontal area of the vehicle and increase the drag coefficient. This is because as the air flows over the top of the vehicle, following the smooth lines of the hood and windshield, then collides with the roof rack and causes turbulence. The removal of this part has led to increases in fuel efficiency in several studies.^[7]

Mud flaps

Mudflaps are now rarely specified as standard on production cars as they interfere with the clean airflow around the vehicle. For larger vehicles such as trucks, mud flaps are still important for their control of spray, and in 2010 a new version of the mud flap was introduced that has been shown to create significantly less aerodynamic drag than standard mud flaps.^[8]

Rear spoiler

A rear spoiler usually comes standard in most sports vehicles and resembles the shape of a raised wing in the rear of the vehicle. The main purpose of a rear spoiler in a vehicle's design is to reduce lift, thereby increasing stability at higher speeds. In order to achieve the lowest possible drag, air must flow around the streamlined body of the vehicle without coming into contact with any areas of possible turbulence. A rear spoiler design that stands off the rear deck lid will increase downforce, reducing lift at high speeds while incurring a drag penalty. Flat spoilers, possibly angled slightly downward may reduce turbulence and thereby reduce the coefficient of drag.^[9] Some cars now feature automatically adjustable rear spoilers, so at lower speed the effect on drag is reduced when the benefits of reduced lift are not required.

Side mirrors

Side mirrors both increase the frontal area of the vehicle and increase the coefficient of drag since they protrude from the side of the vehicle.^[10][11] In order to decrease the impact that side mirrors have on the drag of the vehicle the side mirrors can be replaced with smaller mirrors or mirrors with a different shape. Several concept cars of the 2010s are replacing mirrors with tiny cameras^[12] but this option is not common for production cars because most countries require side mirrors.

Radio antenna

While they do not have the biggest impact on the drag coefficient due to their small size, radio antennas commonly found protruding from the front of the vehicle can be relocated and changed in design to rid the car of this added drag. The most common replacement for the standard car antenna is the shark fin antenna found in most high efficiency vehicles.^[13]

Windshield wipers

The effect that windshield wipers have on a vehicles airflow varies between vehicles; however, they are often omitted from race vehicles and high efficiency concepts in order to maintain the smallest possible coefficient of drag. A much more common option is to replace the windshield wipers with lower profile wipers, or to only remove the windshield wiper on the passenger side of the vehicle, and even to fabricate a deflector to deflect the air up and over the wipers.^[14]

Another alternative is to equip the vehicle with a single wiper placed in the centre of the windshield, allowing it to cover both sides of the windshield. This mitigates the amount of drag by decreasing the frontal area of the blade. While such application may be useful for racing, for most road vehicle this would produce minimal improvement in overall drag reduction.

Fabrication

The application of new parts and concepts onto the vehicle design are easier to include when in the design stage of a vehicle, rather than in aftermarket (automotive) parts, however, the fabrication of these parts assists in the streamlining of the vehicle and can help greatly reduce the drag of the vehicle. Most vehicles with very low drag coefficients, such as race cars and high efficiency concept cars, apply these ideas to their design.^[15]

Wheel covers

When air flows around the wheel wells it gets disturbed by the rims of the vehicles, and forms an area of turbulence around the wheel. In order for the air to flow smoother around the wheel well smooth wheel covers are often applied. Smooth wheel covers are hub caps with no holes in them for air to pass through. This design reduces drag, however, it may cause the brakes to heat up quicker because the covers prevent airflow around the brake system. This is why this modification is more commonly seen with high efficiency vehicles, rather than sports cars or racing vehicles.^[16]

Partial grille block

The front grille of a vehicle is used to direct air directly into the engine compartment. In a streamlined design the air flows around the vehicle rather than through; however, the grille of a vehicle redirects airflow from around the vehicle to through the vehicle, which then increases the drag. In order to reduce this impact a grille block is often used. A grille block covers up a portion, or the entirety of the front grille of a vehicle. In most high efficiency models or vehicles with low drag coefficients there will be a very small grille already built into the design, therefore a grille block is unneeded. The grille in most production vehicles is built generally to have as much air flowing into the engine compartment in order to keep it from overheating. But most commonly there is too much airflow into the engine compartment, preventing it from warming up in a timely manner, so a grille block is used to increase engine performance and reduce the vehicle's drag.^[17]

Under tray

The underside of a vehicle often traps air in various places and adds turbulence around the vehicle. In most racing vehicles this is eliminated by covering the entire underside of the vehicle in what is called an under tray. This tray prevents any air from becoming trapped under the vehicle and reduces drag.^[16]

Fender skirts

Fender skirts are often made as extensions of the body panels of the vehicles and cover the entire wheel wells. Much like smooth wheel covers this modification reduces the drag of the vehicle by preventing any air from becoming trapped in the wheel well and assists in streamlining the body of the vehicle. Fender skirts are more commonly found on the rear wheel wells of a vehicle because the tires do not turn and the design is much simpler. This is commonly seen in vehicles such as the first generation Honda Insight. Front fender skirts have the same effect on reducing drag as the rear wheel skirts, but must be further offset from the body in order to compensate for the tire sticking out from the body of the vehicle as turns are made.^[16]

Modified front bumper

The front bumper is the first part of the vehicle that the air must flow around. Therefore, it plays a crucial role in reducing drag. A front air dam is often used which extends from the very front of the vehicle down to the lowest part of the vehicle. This is done to direct airflow around and over the vehicle rather than allowing air to travel under it. Contoured deflectors, or tire spats, are often made as part of the front bumper in order to direct airflow around the tire without having any increase to the outward flow.

Boattails and Kammbacks

A boattail can greatly reduce a vehicle's total drag. Boattails create a teardrop shape that will give the vehicle a more streamlined profile, reducing the occurrence of drag inducing flow separation.^[18] A kammback is a truncated boattail. It is created as an extension of the rear of the vehicle, moving the rear backward at a slight angle toward the bumper of the car. This can reduce drag as well but a boattail would reduce the vehicles drag more. Nonetheless, for practical and style reasons, a kammback is more commonly seen in racing, high efficiency vehicles, and trucking.^[19]

Typical drag coefficients

The average modern automobile achieves a drag coefficient of between 0.30 and 0.35. SUVs, with their typically boxy shapes, typically achieve a Cd=0.35–0.45. The drag coefficient of a vehicle is affected by the shape of body of the vehicle. Various other characteristics affect the coefficient of drag as well, and are taken into account in these examples. Some sports cars have a surprisingly high drag coefficient, but this is to compensate for the amount of lift the vehicle generates, while others use aerodynamics to their advantage to gain speed and have much lower coefficients of drag.

Some examples of Cd follow. Figures given are generally for the basic model. Some "high performance" models may actually have higher drag, due to wider tires, extra spoilers and larger cooling systems as many basic / low power models have half size radiators with the remaining area blanked off to reduce cooling and engine bay drag.

The Cd of a given vehicle will vary depending on which wind tunnel it is measured in. Variations of up to 5% have been documented^[20] and variations in test technique and analysis can also make a difference. So if the same vehicle with a drag coefficient of Cd=0.30 was measured in a different tunnel it could be anywhere from Cd=0.285 to Cd=0.315.

Production cars Cd Automobile Calendar Year 0.7 to 1.1 typical values for a Formula One car (downforce settings change for each circuit) 0.74 Legends car 0.7 Caterham Seven 0.65 to 0.75 Lotus Seven 1957–1972 0.6 + a typical truck 0.57 Hummer H2 2003 0.54 Mercedes Benz G-Class 0.51 Volkswagen Westfalia Camper 1980-1991 0.51 Citroën 2CV 1948 0.48 Rover Mini 1998 0.48 Volkswagen Beetle (original design)[21][22] 1938 0.48 Volkswagen Cabriolet (Rabbit Convertible)[23] 1979–1993 0.47 Lancia Aprilia[24] 1937 0.46 Ford Mustang (coupe) 1979 0.45 Dodge Viper RT/10 1996 0.45 Mercury Grand Marquis (sedan) 1988-1991 0.45 Range Rover Classic 1990 0.44 Volkswagen Vanagon 1980-1991 0.44 Ford Mustang (fastback) 1979 0.44 Peugeot 305 1978 0.44 Peugeot 504 1968 0.44 Toyota Truck 1990 0.43 TVR 3000S 1978-79 0.425 Duple 425 coach (named for its low Cd by coach standards) 1985 0.42 Lamborghini Countach 1974 0.42 Plymouth Duster 1994 0.42 Triumph Spitfire Mk IV 1971 0.41 Smart Roadster 2003 0.41 Volvo 740 (sedan) 1982 0.405 Subaru Forester 1997-2002[25] 0.40 Mercury Cougar 1983-1986 0.40 Chevrolet Astro 1995-2005[26] 0.40 Ariel Atom 2002[27] 0.40 Ford Escape Hybrid 2005 0.40 Nissan Skyline GT-R R32 1989 0.40 Jaguar XJS 1976-1996 0.39 Chevrolet Tahoe 2006 0.39 Dodge Durango 2004 0.39 Ford Aerostar 1995[28] 0.39 Ford Escort 5 Door 1981-1984[29] 0.39 Honda Odyssey 1994-98 0.39 Triumph Spitfire 1964 0.385 Nissan 280ZX 1978 0.38 FIAT Ritmo 1978 0.38 Ford Territory 2011 0.38 Lexus GX 2003 0.38 Mazda Miata 1989 0.38 Fiat 500 1957 0.38 Smart Roadster Coupé 2003 0.38 Subaru Forester 2009-2013[30] 0.38 VW NewBeetle[31] without wing or spoiler 0.39[32] 2003 0.374 Ford Capri Mk III 1978 0.372 Ferrari F50 1996 0.37 Ford Escort Mk.III (Europe) 1980 0.37 BMW Z3 M coupe 1999 0.37 Jaguar XJ (X300/X308) 0.37 Renault Twingo 0.37 Volkswagen Tiguan 2008 0.36 Alfa Romeo 33 1983[33] 0.36 Cadillac Escalade hybrid 2008 0.36 Cadillac Fleetwood 1996 0.36 Citroën CX (named after the term for Cd) 1974 0.36 Citroën DS 1955 0.36 Chrysler Sebring 1996 0.36 Ferrari Testarossa 1986 0.36 Ford Escort 1997-2002[34] 0.36 Ford Mustang 1999 0.36 Honda Civic 2001–2005 0.36 Mercury Cougar 1987-1988 0.36 Mercury Grand Marquis 1992-1997 0.36 Mitsubishi Magna, V3000 sedan 1985-1991 0.36 Subaru Impreza WRX[35] 2010 0.36 Saturn SW 1996-2001[34] 0.36, 0.244 (1:5) Tatra 87 1936-1950[36] 0.36 Toyota Celica Convertible 1994-1999[37] 0.36 Volkswagen Jetta 1985-1992[38] 0.355 NSU Ro 80 1967 0.355 Ford Focus RS 2016 0.35 Ford Thunderbird 1983-1988 0.35 Aleko 2141 1986-2002 0.35 Aston Martin Vanquish 2004 0.35 BMW M3 Convertible 2005 0.35 BMW Z4 M coupe 2006 0.35 DeltaWing[39] (endurance racing car) 2012 0.35 Dodge Viper GTS 1996 0.35 Honda Del Sol 1992–1997[34] 0.35 Jaguar XKR 2005 0.35 Lexus GX 2010 0.35 Lexus RX 2003–2009 0.35 MINI Cooper 2008 0.35 Nissan Cube 2009 0.35 Renault Clio (Mk 2) 2002[40] 0.35 SSC Ultimate Aero 2007–present 0.35 Tesla Roadster[41] 2008 0.35 Mitsubishi i-MiEV 2011 0.35 Smart ForTwo[42] 2008- 0.35 Toyota MR-2 1998 0.35 Toyota Previa 1991-1997[43][44] 0.35 Toyota Sequoia 2007 0.35 Volvo 940 (sedan) 1990 0.348 Toyota Celica Supra (Mk 2) 1982[45] 0.342 Toyota Celica (Liftback Model) 1982 0.34 Alfa Romeo Giulia sedan 1968-1972 0.34 Aston Martin DB9 2004 0.34 Chevrolet Caprice 1994 0.34 Chevrolet C6 Corvette ZO6 2006–2013 0.34 Chevrolet Tahoe hybrid 2008 0.34 Ferrari 360 Modena 1999 0.34 Ferrari F40 1987 0.34 Ferrari F430 F1 2004 0.34 Ford Puma 1997 0.34 Ford Sierra 1982 0.34 Geo Metro (Hatchback) 1995-1997[34] 0.34 Honda Prelude 1988 0.34 Mercedes-Benz SL (Roof Down) 2001 0.34 Nissan Altima 1993-1997[46] 0.34 Nissan Skyline R34 GT-R 1999-2002[47] 0.34 Peugeot 106 1991 0.34 Saturn SL2 1991-1995[48] 0.34 Subaru Impreza WRX (4 Door) 2009[49] 0.34 Subaru Legacy Wagon 1993-1999[50] 0.34 Toyota Corolla (Wagon) 1993-1997[51] 0.34 Toyota Supra (with factory 3 piece turbo wing) 1989–1990 0.34 Saab 9000 1984-1998 [52] 0.338 Chevrolet Camaro 1995 0.334 Seat Leon FR 2005-2011 0.33 Acura Integra 1993-2001[53] 0.33 Acura RSX 2002-2006[54] 0.33 Alfa Romeo Giulia (saloon) 1962[55] 0.33 Audi A3 2006 0.33 Chevrolet Caprice (sedan) 1991-1996 0.33 Dodge Charger 2006 0.33 Ford Crown Victoria 1992 0.33 Ford Escort ZX2 1998-2003[56] 0.33 Ford Fusion 2010[57] 0.33 Holden Commodore (VT) sedan 1997 0.33 Honda Accord Sedan 2002 0.33 Honda Civic Hatchback 1988-1991[34] 0.33 to 0.37 Koenigsegg Agera (R) 2013 0.33 Lamborghini Murcielago 2001 0.33 Lexus RX 2010 0.33 Mazda RX-7 FC3C 1987 0.33 Nissan 200SX Coupe 1995-1998[58] 0.33 Peugeot 206 1998 0.33 Dodge Durango (without roof-rack), ("HEAT" model, 0.325) 2011–present 0.33 Peugeot 309 1986 0.33 Renault Modus 2004 0.33 Subaru Impreza WRX STi 2004 0.33 Subaru Forester 2014-Current 0.33 Saturn SL2 1999[59] 0.33 Toyota Corolla 1993-1997[34] 0.33 Toyota Supra (without wing) 1989–1990 0.329 Chevrolet Corsica 1989-2006[60] 0.325 Opel Astra J 2009 0.324 Cobalt SS Supercharged 2005 0.321 Toyota Matrix 2003-2008[61]

Production cars (continued) Cd Automobile Calendar Year 0.32 Buick Riviera 1995 0.32 BMW M3 Coupe 2005 0.32 Dodge Avenger 1995 0.32 Ferrari California 2008 0.32 Chrysler 300C 2011-2014 0.32 Fiat Croma 1985-1996 0.32 Ford Taurus 1992-1995[62] 0.32 Geo Metro (Sedan) 1995-1997[34] 0.32 Seat Leon 2005-2011 0.32 Honda Accord (Coupe) 2002 0.32 Honda Ascot Innova (Sedan) 1992-1996 0.32 Honda Civic (Coupe) 1992-1995[34] 0.32 Honda Civic (Hatchback DX) 1996-2000[63] 0.32 Honda Civic (Sedan EX) 1996-2000[64] 0.32 Honda Insight Hybrid [65] 2009- 0.32 Honda NSX 1990 0.32 Hyundai Veloster 2012 0.32 Jaguar XJ (X350) 2006 0.32 Koenigsegg CCX 2006 0.32 Mazdaspeed3 2007 0.32 McLaren F1 1992 0.32 Mercedes-Benz 190E 2.5-16/2.3-16 0.32 Nissan 240SX Coupe 1995-1998[66] 0.32 Nissan 300ZX 1989 0.32 Nissan Altima 1998-2001[67] 0.32 Nissan Maxima 1997 0.32 Oldsmobile Aurora 1995-1999 0.32 Porsche 997 GT2 2008–2013 0.32 Peugeot 406 1995 0.32 Peugeot 806 1994 0.32 Saab Sonett II 1966-1969 [68] 0.32 Scion xB 2008 0.32 Suzuki Swift 1991 0.32 Tatra 600 1948-1952[69] 0.32 Toyota Celica 1994 0.32 Toyota Celica 2000-2005[70] 0.32 Toyota Supra (N/A with wing and turbo models) 1993 0.32 Toyota Supra (with factory turbo wing) 1987–1988 0.32 Toyota Tercel Sedan 1995-2000[71] 0.32 Volkswagen Golf Mk3 1991 0.32 Volkswagen GTI Mk V 2006 0.32 Volvo V50 2004 0.315 Saturn SL1 1996-1999[72] 0.31 Alfa Romeo 156 (1997–2007) 0.31 Audi A4 B5 1995 0.31 Audi A5 2011–present 0.31 Audi A3 2014 0.31 BMW 7-series 2009 0.31 Buick Park Avenue 1996 0.31 Cadillac CTS 2004 0.31 Cadillac CTS-V 2005 0.31 Citroën AX 1986 0.31 Citroën GS 1970 0.31 Eagle Vision 1995 0.31 Fiat Coupé 1995[73] 0.31 Fiat Tipo 1988-1995 0.31 Ford Falcon 1995 0.31 Ford Thunderbird 1989-1997[74] 0.31 Holden Commodore 1998 0.31 Honda Civic (Hatchback) 1992-1995[34] 0.31 Honda Civic (Sedan) 2006 0.31 Infiniti G37 (Coupe) 2008–present[75] 0.31 Kia Rio (Sedan) 2001[76] 0.31 Lamborghini Diablo 1990 0.31 Lexus LFA (wing retracted) 2010 0.31 Mazda MX-3 1990–1996 0.31 Mazda MX-6 1992–1997 0.31 Mazda RX-7 FC3S 1986 0.31 Mazda RX-7 FD R1(R2) 1993 0.31 Mazda RX-8 2004 0.31 Mazda3 (Hatchback) 2010 0.31 Nissan Tiida / Versa 2004 0.31 Opel Tigra 1994-2000 0.31 Pagani Huayra 2012[77] 0.31 Peugeot 307 2001 0.31 Peugeot 405 1987 0.31 Porsche 997 Turbo/GT3 2006 0.31 Renault 25 1984 0.31 Saab Sonett III 1970-1974 [78] 0.31 Saturn SC2 2001 0.31 Scion xA 2004 0.31 Toyota Avalon 1995–2000 0.31 Toyota Corolla 1998-2002[79] 0.31 Toyota Paseo 1995-1999[80] 0.31 Toyota RAV4 2006 0.31 Toyota Camry (Sedan) 1992 0.31 Toyota Supra (N/A; without factory wing) 1993 0.31 Volkswagen GTI Mk IV 1997 0.31 Volkswagen Golf Mk6 2008-2012 0.31 Volvo S40 2nd generation 2003 0.308 Skoda Octavia RS 2005 0.304 Ford Probe 1988-1992[81] 0.30 Alfa Romeo 164 1988[82] 0.30 Audi 100 1983 0.30 Fiat Uno 2nd gen. 1989-2000 0.30 Ford Taurus 1996-1999[83][84] 0.30 Ford Focus ST 2013–present 0.30 Honda Accord Sedan 2003, 2005–2007 0.30 Honda CRX DX/Si[85] 1988 0.30 Honda NSX 2002 0.30 Honda Odyssey 2005 0.30 Hyundai Sonata 2006 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) 2009[86] 0.30 Renault 19 16V 1991 0.30 Saab 92 1947 0.30 Seat Leon 2012 0.30 Toyota Corolla 2003-2008[87] 0.30 Toyota Sienna 2003–2009 0.30 Volkswagen Bora mk4 1999–2005 0.30 Mercedes-Benz CLA BlueEfficiency Edition [88] 2013–Present 0.299 Cadillac ATS 2012 [89] 0.297 Fiat Tempra 1990-1999 0.295 Ford Falcon 1998 0.295 Ford Focus Mk.III hatchback [90] 2011 0.291 Toyota Avalon 2005 0.29 Alfa Romeo 155 1992[91] 0.29 Acura TL 2004-2008 0.29 Audi 80 1991 0.29 Audi A4 2011–present 0.29 BMW 1-Series (116i Sportshatch) 2008 0.29 BMW 8-Series 1989-1999 0.29 BMW i3 2013 0.29 Chevrolet Corvette 2005 0.29 Chevrolet Corvette C5 ZO6 2002 0.29 Daewoo Espero 1990 0.29 Dodge Charger Daytona 1969 0.29 Eagle Talon 1990s 0.29 Fiat Tipo 2015[92] 0.29 Ford Escape 2010[93] 0.29 Ford Falcon (AU) sedan 1998 0.29 Ford Focus C-Max 2003[94] 0.29 FSM Beskid Polish hatchback prototype 1983 0.29 Honda Accord Coupe 2003, 2005–2007 0.29 Honda Accord Hybrid 2005, 2007 0.29 Honda CRX HF[85] 1988 0.29 Infiniti G35 Sedan 2008 0.29 Lancia Dedra 1990 0.29 Lexus CT 200h 2011–present 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 RX-7 FD 1993 0.29 Mazda3 2010 0.29 Mercedes-Benz SL (Roof Up) 2001–present 0.29 Mercedes-Benz C-Class Sportscoupe 2001 0.29 Nissan 350Z Coupe Track and Grand Touring 2007–2008 0.29 Nissan Versa 2007–2008 0.29 Opel Calibra (16v / V6 / Turbo versions) 1989-1997 0.29 Peugeot 208 2012 0.29 Peugeot 308 2007–present 0.29 Peugeot 407 2004-2011 0.29 Peugeot 607 2000-2010 0.29 Pontiac Firebird Trans Am (with optional W62 Aero Package and N89 Turbo Cast rims) 1984 0.29 Porsche 918 2010 0.29 Porsche Boxster 2005–present 0.29 Subaru SVX (Without factory spoiler) 1992 0.29 Toyota Camry 1996–2001 0.29 Toyota Echo 2000-2005[95][96] 0.29 Toyota Prius 2001 0.29 Toyota Yaris 2006-2011 0.29 Volvo 850 T-5R sedan 1995 0.29 Volvo C70 2000 0.29 Nissan Leaf 2010 [97] 0.288 Chrysler Concorde 1998–2001 0.286 Chevrolet Corvette C6 2005–present 0.285 Opel Astra K 2015 0.285 Chevrolet Volt 2016 0.284 Volkswagen Passat CC 2008–present 0.281 Chevrolet Volt 2010-2015 0.28 Audi A2 1.4 TDI 2000 0.28 Citroën C4 2004 0.28 Citroën XM 1989 0.28 Fiat Croma Nuova 2005-2011 0.28 Honda Civic Hybrid 2003-2005[34] 0.28 Hyundai Elantra 2011 0.28 Hyundai Sonata (0.25 for the Hybrid) 2011-2013 0.28 Lexus IS 2006–present 0.28 Lexus LS400 1998 0.28 Luxgen5 Sedan 2011 0.28 Mazda3 (Hatchback) 2012 0.28 Mercedes-Benz E-Class 1985-1996 0.28 Mitsubishi Diamante, Magna and Verada 1995, 1996 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 0.34 Saab 900 NG 2003 [98] 0.31 Saab 9-3 Viggen 2003 [99] 0.28 Saab 9-3 SS 2003 [100] 0.33 Saab 9-3 SC 2003 [101] 0.29 Saab 9-5 (1998 – 2009) 2003 [102] 0.31 Saab 9-5 Wagon (2000-2010) 2003 [103] 0.28 Toyota Camry / Lexus ES 2001 0.28 Chevrolet Cruze sedan [104] 2015 0.277 Toyota Auris hatchback 2013 0.275 Ford Fusion 2013[105] 0.274 Ford Focus Mk.III sedan [90] 2011 0.27 Audi A2 1.6 FSI 2003 0.27 Honda Civic Hybrid 2006- 0.27 Hyundai Genesis 2009 0.27 Infiniti G35 Coupe (0.26 with "aero package") 2003–2007 0.27 Lexus GS 2005 0.27 Mazda6 2009 0.27 Mazda6 (sedan and hatchback)[106] 2008 0.27 Mercedes-Benz W203 C-Class Sedan 2001 0.27 Mercedes-Benz S Class (0.268 with Sport Package) 2000–2005 0.27 Nissan GT-R 2007–2010 0.27 Subaru BRZ and Toyota 86 2012[107] 0.27 Toyota Camry Hybrid (XV40 & XV50) 2007, 2011 0.27 Volkswagen Golf Mk7 2012–present 0.27 Volkswagen Passat B5 (sedan) 1997 0.26 BMW E90 (0.26-0.30) 2009[108] 0.26 BMW i8 2014 0.26 Jaguar XE[109] 2014 0.26 Lexus LS 430 (without air suspension) 2001–2006 0.26 Lexus LS 460 2006 0.26 Mazda3 (Sedan) 2012[110] 0.26 Mercedes-Benz B-Class + eco-package 2012- 0.26 Mercedes-Benz C-Class Coupe[111] 2015–Present 0.26 Mercedes-Benz E-Class 2002-2009 0.26 Mercedes-Benz W221 S-Class 2006–present 0.26 Infiniti Q50 2013–present 0.26 Nissan GT-R 2011–present 0.26 Opel Calibra (8 valve version) 1989 0.26 Toyota Prius 2004–2009 0.26 Citroen SM 1970 0.25 Peugeot 508 2011–present 0.25 Lexus LS 430 (with air suspension) 2001–2006 0.25 Audi A2 1.2 TDI 2001 0.25 Honda Insight 1999-2006 0.25 Hyundai Sonata Hybrid 2013 0.25 Toyota Prius 2010-2015 0.2455 (1:5) Tatra 77 1933 0.24 Mercedes-Benz S-Class[112] 2014–Present 0.24 Mercedes-Benz C-Class Sedan[113] 2014–Present 0.24 Hyundai Sonata Hybrid 2016 0.24 Tesla Model S[114] 2012 0.24 Tesla Model X[115] 2015 0.24 Toyota Prius[116] 2016 0.212 (according to some sources: 1:5 model test)[117][118][119] Tatra T77A 1935[120] [121] [122] [123] 0.21 Tesla Model 3[124] 2017 0.195 General Motors EV1 1996 0.189 Volkswagen XL1 2013

Concept/experimental cars Cd Automobile Calendar Year 0.27 Avion[125] 1986 0.26 Alfa Romeo Disco Volante 1952 0.25 Dymaxion Car 1933 0.25 SmILE (an experimental car) 1996 0.22 BMW Vision EfficientDynamics Concept 2009 0.22 Citroën ECO 2000 Concept 1981[126] 0.22 Aurel Persu Streamliner 1923[127] 0.20 Opel Eco-Speedster 2002[128] 0.20 Loremo Concept 2006 0.19 Alfa Romeo B.A.T. 7 Concept 1954 0.19 Dodge Intrepid ESX Concept 1995 0.19 General Motors Ultralite 1992 0.19 Mercedes-Benz Bionic Concept[129](based on the boxfish) 2005 0.170 Chrysler Ghia Dart 1955[130] 0.17 Pininfarina Fiat 124 concept (Morelli shape) 1978 0.168 Daihatsu UFE-III Concept 2005[131] 0.16 General Motors Precept Concept (5 seats)[132] 2000 0.16 Edison2 Very Light Car, Automotive X Prize winner[133] 2010 0.159 Volkswagen 1-litre car Concept 2002 0.157 Li-ion Motors Wave II, Automotive X Prize winner[134] 2010 0.15 Schlörwagen[135] 1939 0.15 Aptera 2 Series 2e Prototype 2011 0.15 Keris RV Nakoela Team(Shell Eco-marathon) Prototype 2015 0.149-0.150 Urbee 2 [136] 2013 0.147 JCB Dieselmax land speed record holder 2006 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[137] 0.117 Summers Brothers Goldenrod Bonneville race car 1965 0.08 Fortis Saxonia (Shell Eco-marathon) Concept 2007 0.072 Alérion Supermileage (Shell Eco-marathon) Prototype 2013 0.07 Nuna, World Solar Challenge winner 2001–2007 0.0512 Ecorunner V (Shell Eco-marathon) Prototype 2015[138]

Drag area

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 product of drag coefficient and area - drag area - is represented as CdA (or CxA), a multiplication of the Cd value by the area.

The term drag area derives from aerodynamics, where it is the product of some reference area (such as cross-sectional area, total surface area, or similar) and the drag coefficient. In 2003, Car and Driver magazine adopted this metric as a more intuitive way to compare the aerodynamic efficiency of various automobiles.

The force required to overcome drag is:

$\tfrac{1}{2} \times \text{drag coefficient} \times \text{air density} \times \text{drag area} \times \text{speed}^2$

As drag area CdA is the fundamental value that determines power required for a given cruise speed it is a critical parameter for fuel consumption at a steady speed. This relation also allows an estimation of the new top speed of a car with a tuned engine,

$\text{estimated top speed} = \text{original top speed} \times \sqrt[3]{\frac{\text{new power}}\text{original power}}$

Or the power required for a target top speed,

$\text{power required} = \text{original power} \times \left( \frac{\text{target speed}}{\text{original speed}} \right)^3$

Average full-size passenger cars have a drag area of roughly 8.50 sq ft (0.790 m²). Reported drag areas range from the 1999 Honda Insight at 5.1 sq ft (0.47 m²) to the 2003 Hummer H2 at 26.5 sq ft (2.46 m²). The drag area of a bicycle is also in the range of 6.5–7.5 sq ft (0.60–0.70 m²).^[139]

Automobile examples of CdA^[140]

CdA sqft	CdA m2	Automobile model
2.04 sq ft	0.190 m^2	2011 Aptera 2 Series[141]
2.10 sq ft	0.195 m^2	2013 Urbee 2[142]
2.50 sq ft	0.232 m^2	1986 Twike[143]
2.54 sq ft	0.236 m^2	2002 Opel Eco-Speedster [144]
2.69 sq ft	0.250 m^2	2009 Loremo
2.784 sq ft	0.2586 m^2	2010 Edison2 Very Light Car [145]
3.00 sq ft	0.279 m^2	2011 Volkswagen XL1
3.95 sq ft	0.367 m^2	1996 GM EV1
5.00 sq ft	0.465 m^2	2005 Mercedes-Benz Bionic[146]
5.10 sq ft	0.474 m^2	1999 Honda Insight
5.40 sq ft	0.502 m^2	1989 Opel Calibra (8 valve)
5.58 sq ft	0.518 m^2	1993 Mazda RX-7 FD (base model) [147]
5.70 sq ft	0.530 m^2	1985 Subaru Alcyone/XT/Vortex
5.71 sq ft	0.530 m^2	1990 Honda CR-X Si
5.74 sq ft	0.533 m^2	2002 Acura NSX
5.76 sq ft	0.535 m^2	1968 Toyota 2000GT
5.80 sq ft	0.539 m^2	1986 Toyota MR2
5.81 sq ft	0.540 m^2	1989 Mitsubishi Eclipse GSX
5.86 sq ft	0.544 m^2	2001 Audi A2 1.2 TDI 3L
5.88 sq ft	0.546 m^2	1990 Nissan 240SX / 200SX / 180SX
5.90 sq ft	0.548 m^2	2015 BMW i8 [148]
5.92 sq ft	0.550 m^2	1994 Porsche 911 Speedster
5.95 sq ft	0.553 m^2	1990 Mazda RX7
5.96 sq ft	0.554 m^2	1993 Mazda RX-7 FD R1(R2) [149]
6.00 sq ft	0.557 m^2	1992 Subaru SVX
6.00 sq ft	0.557 m^2	1970 Lamborghini Miura
6.08 sq ft	0.565 m^2	2008 Nissan GTR
6.08 sq ft	0.565 m^2	1989 Geo Metro [34]
6.13 sq ft	0.569 m^2	1991 Acura NSX
6.17 sq ft	0.573 m^2	1995 Lamborghini Diablo
6.19 sq ft	0.575 m^2	1981 Citroën GSA X3 [150]
6.20 sq ft	0.576 m^2	2012 Tesla Model S P85 [151]
6.20 sq ft	0.576 m^2	2014 Toyota Prius
6.24 sq ft	0.580 m^2	2004 Toyota Prius
6.27 sq ft	0.583 m^2	1986 Porsche 911 Carrera
6.27 sq ft	0.583 m^2	1992 Chevrolet Corvette
6.35 sq ft	0.590 m^2	1999 Lotus Elise
6.37 sq ft	0.592 m^2	2000 Vauxhall VX220 N/A
6.40 sq ft	0.595 m^2	1990 Lotus Esprit
6.41 sq ft	0.596 m^2	2003 Smart Roadster Coupé
6.54 sq ft	0.608 m^2	1991 Saturn Sports Coupe
6.57 sq ft	0.610 m^2	1985 Chevrolet Corvette
6.63 sq ft	0.616 m^2	2001 Audi A2
6.66 sq ft	0.619 m^2	1996 Citroën Saxo
6.70 sq ft	0.622 m^2	2014 Chevrolet Volt
6.77 sq ft	0.629 m^2	1995 BMW M3
6.79 sq ft	0.631 m^2	1993 Toyota Corolla DX
6.80 sq ft	0.632 m^2	2007 BMW 335i Coupe
6.81 sq ft	0.633 m^2	1991 Subaru Legacy
6.90 sq ft	0.641 m^2	1993 Saturn Wagon
6.93 sq ft	0.644 m^2	1982 Delorean DMC-12
6.94 sq ft	0.645 m^2	2003 Smart Roadster
6.96 sq ft	0.647 m^2	1988 Porsche 944 S
7.00 sq ft	0.650 m^2	2013 Mercedes-Benz CLA250[152]
7.02 sq ft	0.652 m^2	1992 BMW 325I
7.04 sq ft	0.654 m^2	1991 Honda Civic EX
7.06 sq ft	0.656 m^2	2004 Vauxhall VX220 Turbo
7.10 sq ft	0.660 m^2	1995 Saab 900
7.11 sq ft	0.661 m^2	1991 Ford Thunderbird LX
7.13 sq ft	0.662 m^2	1970 Citroën SM [153]
7.14 sq ft	0.663 m^2	1995 Subaru Legacy L
7.20 sq ft	0.669 m^2	1995 Nissan Maxima GLE
7.34 sq ft	0.682 m^2	2001 Honda Civic
7.39 sq ft	0.687 m^2	1994 Honda Accord EX
7.48 sq ft	0.695 m^2	1993 Chevrolet Camaro Z28
7.57 sq ft	0.703 m^2	1992 Toyota Camry
7.63 sq ft	0.709 m^2	1974 Citroën CX [154]
7.69 sq ft	0.714 m^2	1994 Chrysler LHS
7.72 sq ft	0.717 m^2	1993 Subaru Impreza
7.80 sq ft	0.725 m^2	2012 Nissan Leaf SL
8.02 sq ft	0.745 m^2	2005 Bugatti Veyron
8.70 sq ft	0.808 m^2	1990 Volvo 740 Turbo
8.70 sq ft	0.808 m^2	1992 Ford Crown Victoria
8.71 sq ft	0.809 m^2	1991 Buick LeSabre Limited
8.79 sq ft	0.817 m^2	1956 Citroën DS Spécial [155]
9.54 sq ft	0.886 m^2	1992 Chevrolet Caprice Wagon
10.7 sq ft	0.99 m^2	1992 Chevrolet Blazer
11.6 sq ft	1.08 m^2	2005 Ford Escape Hybrid
11.7 sq ft	1.09 m^2	1993 Jeep Grand Cherokee
12.2 sq ft	1.13 m^2	1949 Nash Airflyte
16.8 sq ft	1.56 m^2	2006 Hummer H3
17.4 sq ft	1.62 m^2	1995 Land Rover Discovery
26.5 sq ft	2.46 m^2	2003 Hummer H2

See also

• Automotive aerodynamics
• Drag (physics)
• Drag equation
• Paul Jaray

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External links

• Further 500 drag coefficients
• Improving Aerodynamics to Boost Fuel Economy
• Tel Aviv University reduces drag on trucks by 10%
• Simple roll-down test for measuring Cd and Crr for cars and bikes