What is the so-called contact pressure?

Thomas Wachsmuth 23 April 2022 Tips, products, information & Co.

Reading time 4 Min.

In racing cars or super sports cars, the weight acts perpendicularly to the road when they are not moving. He comes into motion dynamic contact pressure as reverse lift through the body or through custom wings moreover. As a reversal of lift, this force is used in motorsport as downforce referred to and in English too down force called. Downforce is an aerodynamic effect and depends on speed and the square of the surrounding air. The higher the speed, the stronger the contact pressure.

Spoilers & Co. for more contact pressure

The increased contact pressure acts on the wheel load and thus improves the (adhesive) friction of the wheels on the road. This allows the tires to develop higher cornering forces, allowing the vehicle higher cornering speeds can reach. In addition, the rear wheels, especially in racing cars, are stabilized by the stronger contact pressure and the connection to the road is improved. Otherwise they could spin due to the sharp increase in air resistance when driving fast and thus transfer less power into propulsion. With the help of various means, designers try to increase the contact pressure in a targeted manner. Here there are:

Front or rear wings
Subsoil smoothing (because of negative ground effects)

"Inverted wing profile" as a combination of the smooth underbody with a diffuser
additional aerodynamic means such as Venturi channels

While the wings and other measures use the air resistance in a targeted manner to generate contact pressure, i.e. downforce, spoilers have the opposite effect. They act as air deflectors and redirect the ambient air so that the Buoyancy of the vehicle is disturbed. There is no downward aerodynamic force, just a redirection of the airflow around the body. A contact pressure-generating wing increases the air resistance. A high downforce is important so that the car can use its power to the full, thus enabling high speed both on the straight (against air resistance) and in curves. Vehicle designers must therefore decide which of the two opposing effects they want to use and how many parts they want to use.

Contact pressure in Formula 1 racing cars!

In order to be able to drive at high speeds in Formula 1, the vehicles generate more contact pressure than their total weight. A Formula 1 car that weighs 620 kg including the driver generates a contact pressure of 240 kN at 16 km/h if it has a resistance value of 0,93. That's about the same 2,7 times of the total weight of the vehicle. As a result, a lateral acceleration of up to 3,7 g possible. If the coefficient of static friction is around 1,8, the maximum lateral acceleration is 4,5 g. Due to this downforce, racing cars can theoretically drive on the ceiling from a certain speed without falling due to gravity. The additional downforce is used in Formula 1 racing cars to achieve higher speeds by better overcoming air resistance. The data of a Ferrari F1-2000 are in the following table zu finden:

components	$What is the so-called contact pressure?$	$What is the so-called contact pressure?$	share of the output in percent
Front wing	0,123	0,9699	36,9
rear wing	0,297	0,899	34,4
underbody (diffuser)	0,099	1,080	41,3
wheels in front	0,150	−0,038	−1,4
rear wheels	0,187	−0,061	−2,3
baffles	0,023	−0,020	−0,8
Rest	0,055	−0,210	−8,0
Total	0,932	2,617	100

drive coefficients cA and drag coefficients cw refer to the entire vehicle surface. Info: Wikipedia

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