DRAG COEFFICIENT FOR CARS

by SANDHYA

Concept of Drag

• Drag is the retarding force exerted on a moving body.

• It attempts to slow down the moving body.• It is a function of the speed of the body, the

size (and shape) of the body, and the medium through which it is moving

Drag Force Due to Air

• The drag force due to wind (air) acting on an object can be found by:

FD = ½ ρ CDV2A

where: FD = drag force (N)CD = drag coefficient (no units)V = velocity of object (m/s)A = projected area (m2)ρ = density of air (kg/m3) {1.2 kg/m3}

• Generally the size of a vehicle and its frontal area is determined by the design requirements.

• Consequently efforts to reduce drag are concentrated on reducing the drag coefficient by proper shaping of the body..

Drag Coefficient: CD

• The drag coefficient is a function of the shape of the object and the Reynolds Number (Re)– Re = (velocity * length-scale) / (kinematic viscosity)

• For a full-size truck, a change in drag coefficient of 0.01s approximately equal to an improvement in fuel economy of 0.1 mpg on the combined city/highway driving cycle.

• The same drag coefficient reduction can improve a car's fuel economy by approximately 0.2 mpg.

Typical drag coefficients

• The average modern automobile achieves a drag coefficient between 0.30 and 0.35.

• SUVs(sport utility vehicle), with their typical 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 to reduce lift.

• Some "high performance" models may actually have higher drag, due to wider tires and extra spoilers.

Drag coefficient

Cd

Old Car like a T-ford 0.7 - 0.9

Modern Car like Toyota Prius 0.26

Sports Car, sloping rear 0.2 - 0.3

Convertible, open top 0.6 - 0.7

Common Car like Opel Vectra (class C) 0.29

Drag coefficientMake Model Year Cd

Acura CL 1997 - 1999 0.34

Acura CL 2000 - 2003 0.32

Acura Integra 1994 - 2001 0.32

Acura NSX 1995 - 2005 0.32

Acura RSX 2002 - 2004 0.32

Acura TSX 2004 - 2008 0.27

Make Model Year Cd

Audi A3 1996 - 2003 0.31

Audi A4 1994 - 2001 0.29

Audi A6 1997 - 2004 0.29

Audi A8 1994 - 2002 0.28

Make Model Year Cd

BMW Compact 1993 - 2000 0.31

BMW 3-series 1990 - 1999 0.30

BMW 5-series 1995 - 2003 0.27

BMW 7-series 1994 - 2001 0.30

Make Model Year Cd

Mercedes-Benz C-class 1993 - 2000 0.30

Mercedes CL500 1998 - 2000 0.28

Mercedes-Benz E-class 1995 - 2002 0.27

Mercedes-Benz G-class 1990 - 0.53

Mercedes-Benz S-class 1991 - 1999 0.31

Mercedes SL600 1989 - 2002 0.45

Mercedes-Benz Vito 1996 - 2003 0.34

Fiat Bravo 1995 - 2001 0.32

Fiat Cinquecento 1991 - 1998 0.33

Fiat Punto 1993 - 1999 0.30

Fiat Ulysse 1994 - 2003 0.34

Make Model Year Cd

Ford Aspire 1994 - 1997 0.36

Ford Escort (Euro) 1995 - 2000 0.32

Ford Escort 1997 - 2002 0.36

Ford Explorer II 1995 - 2001 0.43

Ford F-150 Lightning 1999 - 2004 0.36

Ford Fiesta 1995 - 2002 0.36

Ford Galaxy 1995 - 2000 0.32

Ford Ka 1996 - 2008 0.35

Ford Maverick 1988 - 1994 0.52

Ford Mondeo 1996 - 2000 0.31

Ford Mondeo Turnier 1996 - 2000 0.32

Ford Ranger 2001 0.49

Ford Scorpio 1985 - 1998 0.32

Ford SVT Mustang Cobra 1994 - 2004 0.37

Ford Thunderbird 1989 - 1997 0.31

Make Model Year Cd

Honda Accord Ex Coupe 1998 - 2002 0.34

Honda Civic 1988 - 1991

Honda Civic Hatch 1988 - 1991 0.33

Honda Civic Coupe 1992 - 1995 0.32

Honda Civic 2001 - 2005

Honda Civic Coupe 2006 - 0.29

Honda Civic Del Sol 1992 - 1997 0.35

Honda Civic Hatch 1992 - 1995 0.31

Honda Civic Hatch 1996 - 2000 0.36

Honda Civic Sedan 1996 - 2000 0.32

Honda Civic Hybrid 2003 - 2005 0.28

Honda Civic Hybrid 2005 - 0.27

Honda Civic SI 1996 - 2000 0.34

Honda CRX 1984 - 1987 0.32

Honda CRX 1988 - 1991 0.30

Honda CRX HF 1988 - 1991 0.29

Honda Insight 2000 - 2006 0.25

Make Model Year Cd

Volkswagen 1L Concept 0.15

Volkswagen Beetle 1998 - 0.38

Volkswagen Beetle 1959 - 1979 0.48

Volkswagen Caravelle/Transporter

1990 - 2003 0.37

Volkswagen Golf 1997 - 2003 0.32

Volkswagen Golf Variant 1997 - 2003 0.34

Volkswagen Jetta 1993 - 1999 0.30

Volkswagen Jetta 1986-1992 0.36

Volkswagen Jetta sedan 2000 - 2005 0.30

Volkswagen Jetta 2006 - 0.31

Volkswagen Jetta wagon 2000 - 2005 0.30

Volkswagen Passat 1995 - 1997 0.31

Volkswagen Passat Wagon 1995 - 1997 0.33

Volkswagen Polo 1994 - 2002 0.33

Volkswagen Sharan 1995 - 2000 0.32

Volkswagen Vento/Jetta 1992 - 1999 0.32

Make Model Year Cd

Jeep Cherokee 1984 - 2001 0.52

Jeep Grand Cherokee 1993 - 1998 0.42

Jeep Wrangler TJ-Hardtop 1997-2005 0.55

Jeep Wrangler TJ-Soft Top 1997-2005 0.58

Mazda 626 1992 - 1997 0.29

Mazda Xedos 9/Millenia 1993 - 2003 0.28

Mazda MX-3 1992 - 1995 0.32

Nissan Cube 2008 - 0.35

Nissan Leaf 2011 - 0.28

Nissan Maxima 1995 - 1999 0.32

Škoda Felicia 1994 - 2001 0.346

Škoda Octavia 1996 - 0.32

Toyota Prius 2010 - 0.25

Toyota Sienna 2011 - 0.309

Toyota Supra 1993 - 2002 0.32

General Motors EV1 1996 0.19

To improve CdTo improve Cd, designers may make the following changes: • Round the edges of the front end• Tune the grille and fascia openings• Tune the wheel openings• Place spats (small spoilers) in front of the tires to reduce turbulence• Tune the size and shape of the outside mirrors and their attachment arms• Add side skirts• Tune the deck height, length and edge radius• Install a rear spoiler• Adjust the angle of the rear window• Tuck up the exhaust system• Use a diffuser to tune air coming off the underside• Install "belly pans," underbody panels that cover components and smooth airflow

THANK U