contact pressure

In sports cars , super sports cars and racing cars , the contact pressure generates a force acting vertically on the road in addition to the weight force. It is created by downward dynamic lift on the body or on attached wings . The English term downforce or downforce is often used in motorsport . As an aerodynamic effect , the contact pressure depends on the speed in relation to the surrounding air squared. It increases sharply at higher speeds.

An increased contact pressure enables a higher cornering speed limit , because it increases the wheel load , so that a higher (static) friction of the tires on the road enables the wheels to transfer greater cornering forces to the road. The rear wheels of sports cars would also spin at high speeds without extra contact pressure, since the air resistance then increases sharply - the transmission of a corresponding propulsive force requires the best possible connection between the tires and the road. Therefore, designers try to specifically generate or increase the contact pressure through design measures. These include:

• Front or rear wing ,
• negative floor effect (smooth sub-floor),
• Diffuser , together with the smooth underbody, can form an "inverted wing profile", or
• other aerodynamic measures (for example venturi channels , rarely).

A spoiler, on the other hand, is an air deflector or deflector and does not generate any downward aerodynamic lift, but instead disrupts the lift generated by the air flow around the body of a car or otherwise interferes with the flow around the body.

The wing mechanism, which generates contact pressure, increases the air resistance. Due to the contact pressure, however, the vehicle can bring more power to the road - which is necessary to achieve high speed against air resistance and higher cornering speeds. So there are two opposing effects that the vehicle developer has to weigh up.

formula 1

Formula 1 vehicles develop more contact pressure than their own weight. At 240 km / h, for example, a Formula 1 racing car achieves 16  kN downforce (with a value of 0.93), which is 2.7 times its weight of 620 kg (vehicle including driver). The car could thus “drive on the ceiling”, but it also needs the additional contact pressure to overcome air resistance. The racing car achieves a possible lateral acceleration of 3.7  g , with a coefficient of static friction of 1.8 a lateral acceleration of 4.5 g. ${\displaystyle c_{\mathrm {w} }}$

The following table shows data from the Ferrari F1-2000 from the year 2000:

component	${\displaystyle c_{\mathrm {w} }}$	${\displaystyle c_{\mathrm {A} }}$	Share of downforce 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
Front wheels	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

The individual drag coefficients and downforce coefficients refer to the entire area of ​​the vehicle. ${\displaystyle c_{\mathrm {w} }}$ ${\displaystyle c_{\mathrm {A} }}$

See also

• Kamm circle

Individual evidence

1. ↑ ^{a b} Michael Trzesniowski: Rennwagentechnik , Vieweg and Teubner Verlag, Wiesbaden, 2nd edition 2010, ISBN 978-3-8348-0857-8 , page 137
2. ↑ Formula 1 racing cars can drive upside down on the ceiling. Right? , Time online.
3. ^ Bosch: Kraftfahrtechnisches Taschenbuch , 26th edition 2007, ISBN 978-3-8348-0138-8 , p. 435
4. ^ Wright, P .: Ferrari Formula 1. Under the skin of the Championship-winning F1-2000, SAE International, 2004 ISBN 978-076801341-2