How a Car Works · Chapter 08
Below town speeds the air is barely worth mentioning. Above about 100 km/h it quietly becomes the strongest force on the car — the thing your fuel is really spent fighting, and, for racing cars, a resource worth more than engine power.
· THE CUBE LAW
Air resistance grows with the square of speed — but the power to overcome it grows with the cube, because you are pushing a harder force at a higher speed. Drive twice as fast and the air demands eight times the power. This single law explains most of motoring: why fuel economy collapses on the motorway, and why a car needing 20 kW to hold 100 km/h needs 160 to hold 200.
DEMOGear RatiosWatch the drag curve sink the tractive-force sawtooth at top speed.TAKEAWAYForce grows with speed squared, power with speed cubed — twice as fast costs eight times the power.
· THE SHAPE
What the air charges depends on two things you can design: the car’s frontal area and its drag coefficient — how cleanly the flow closes behind it. The messy part is the back: air that separates off a bluff tail leaves a churning low-pressure wake that drags the car backwards like a parachute.
TAKEAWAYA cleaner shape is worth real horsepower at every speed, forever, for free.
· DOWNFORCE
Racing asked a different question: chapter 6 said grip scales with load — so could the air be made to press the car down? Bolt on a wing from the planes track, invert it, and every km/h of speed buys clamping force that costs no weight. The bill is drag: every kilogram of downforce is bought with a slice of top speed.
DEMODownforce & BalanceTrim the wings and floor yourself — grip vs the drag wall, live.READ1968: the first wingsWings arrive in Formula 1 — on stilts, bolted to the Lotus 49.TAKEAWAYDownforce is lift re-aimed at the tarmac — grip bought with speed instead of weight.
· GROUND EFFECT
The cleverest trick uses the road itself. Squeeze the airflow through the narrowing gap under the car and it speeds up, dropping its pressure — and the whole floor becomes a suction pad. The Lotus 79 sealed that channel with sliding skirts and dominated its era; its descendants do it with sculpted tunnels and diffusers.
READThe diffuser: the pump at the backThe exit ramp that lets the floor breathe — and the stall cliff one degree past its sweet spot.READThe Lotus 79’s skirtsSealing the tunnel — ground effect’s defining trick, up close.TAKEAWAYGround effect is downforce almost without drag — banned, re-invented, re-banned, finally re-embraced.
The most regulated square metres in motorsport are the undersides of Formula 1 cars.
FOR THE SELF-CHECK