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Coefficient of drag has nothing to do with size | Know it All with Jason Cammisa | Ep. 12 - Hagerty Media
Drag coefficient describes a car’s shape — not its size. Think of it as a coupon code that reduces or increases a car’s effective frontal area, the measure of how big the air sees it.
A low Cd can make a huge difference in a vehicle’s overall aerodynamic drag. A Tesla Model X has 1.6 times the frontal area of a Lotus Elise SC, and yet its overall drag is lower. Meaning: to the air, the tiny Lotus is actually a bigger car.
Watch for more colorful, humorous insights on the definition of the coefficient of drag.
but it does for cross sectional area. the drag force is:
Fad = 0.5 · Cd · A · ρair · (v – vwind)^2
where:
Fad [N] – aerodynamic drag force
Cd [-] – aerodynamic drag coefficient
A [m2] – maximum cross-section area of the vehicle
ρair [kg/m3] – air density (equal to 1.202 kg/ m3 for dry air at 20 °C and 101.325 kPa)
v [m/s] – vehicle speed
vwind [m/s] – wind speed
the air has to move out of the way for the car to go through it. it also depends on the shape (where does the air flow separate from the vehicle, the earlier the separation, the higher the drag force), the smoothness and type of paint (how tightly does the air attach to the vehicle, the tighter it attaches, the higher the drag; this is part of the Cd)