Dealing With Downforce

Contrails off this rear wing are one of the few visual cues into the detailed and crucial-to-performance world of aerodynamics.
Contrails off this rear wing are one of the few visual cues into the detailed and crucial-to-performance world of aerodynamics.
Contrails off this rear wing are one of the few visual cues into the detailed and crucial-to-performance world of aerodynamics.

The harsh reality of modern motorsport is that it relies almost too much on aerodynamics. Whether it be for cooling or downforce, the shape of the body plays a somewhat larger role than the tires or the engine do, and ultimately, that means that in order to be successful, a thorough understanding of how to get the air around one’s car working best for them is imperative. Downforce can come through wings and undertrays, ground effects and diffusers affects vehicle behavior when following another closely, improves certain areas of performance, and adds another challenge to the overall driving experience. Finding the limit in a downforce-laden car isn’t something that is intuitive or organic, but it’s crucial – absolutely crucial – to winning in everything from a Formula Ford 2000 all the way to a LMP1 machine.
Low Pressure Means Grip
Basically, downforce functions on a basic principle, which goes by the name of Bernoulli’s. This states that when airflow increases speed, air pressure decreases and a lifting force is enacted in the opposite direction. So, air traveling over a the longer, curved edge of a wing will travel faster than air traveling over a straightened edge. Therefore, if the curved, longer edge of the wing is facing upwards, then at speed, air pressure will push the car downwards, hence downforce. This is the theory which makes flight possible, albeit in the reverse direction, so rather than wings providing lift, they push the car and the tires into the ground, increasing grip and traction.

Here, air traveling faster over a longer, lower edge of the wing corresponds with a reduction in pressure.
Here, air traveling faster over a longer, lower edge of the wing corresponds with a reduction in pressure.

Chasing Ground Effect
Wings were not fully understood until the mid-seventies, and even then they were fairly rudimentary. As time pressed on, clever minds pushing the aerodynamic envelope began experimenting with different ways to harness airflow to push their machines into the ground. At the onset of the 1980s, designers began experimenting with the undertray of their racing cars, finding ways to reduce the amount of lift that comes from airflow underneath the car, and turn that airstream into downforce. This
went on to be known as ground effect.

 

The Porsche 962's venturi tunnels expand air towards the rear of the car, resulting in a low pressure situation, resulting in downforce.
The Porsche 962’s venturi tunnels expand air towards the rear of the car, resulting in a low pressure situation, resulting in downforce.

In the case of sports cars, the underbody tunnel became immensely popular, as seen in the Porsche 956 and later the 962. The tunnel directed airflow from the sides of the car and sent it through a tunnel which would expand as it reached the end of the car. This expansion had the effect of lowering the air pressure, again generating downforce. This style of underbody, linked to a diffuser, built grip more progressively and allowed the heavier sports cars of the era to compete with the lighter, more powerful, contemporary F1 machines.

 The Porsche 956, and later the 962, pushed underbody development in the mid-eighties.

The Porsche 956, and later the 962, pushed underbody development in the mid-eighties.

With narrow formula cars, ground effect initially involved sliding skirts, which boxed off the edges of the car and sealed the air in underneath. Although the downforce was predominantly created by a curved underbody, these skirts prevented outside air from entering the underbody area to try and equalize the pressure. With this form of ground effect, the cars developed immense grip and lap times were slashed by huge margins in the course of several years. These cars were not easy to drive, however, as the cornering loads they were capable of were compensated for by using incredibly stiff suspension. Additionally, these cars were nervous and unpredictable on the limit and developed and lost grip in a very dramatic fashion. They were not popular among drivers, and were eventually banned because when the cars left contact with the ground and the seal was broken, the level of grip changed drastically, and the formula was deemed too dangerous.

Driving with Downforce
Wings will increase grip exponentially – until the tire gives up – but only begin to do so when there’s enough air flowing over them to push the car into the ground. Typically, this begins around sixty miles an hour, but it becomes increasingly more effective with more speed. What this means, however, is that a great deal of turbulence is produced, and following closely behind another car at speed can be troublesome as the airflow to one’s own set of wings is diminished due to the turbulence up front, and grip is subsequently lost. This is often referred to as “aero push,” and will rapidly wear tires, so it pays not to linger too long behind an opponent’s gearbox. This might be the most pronounced setback a winged car’s driver must deal with.

What wings do well is improve braking and cornering grip. Predictably, as the car enters a fast corner and the wings are beginning to work, the tires are pressed into the asphalt, and the car effectively weighs more than it does at rest. It isn’t easy to come to terms with this concept since it requires the driver to fight with their natural instincts. Going faster into a corner and expecting a corresponding increase in grip is very counter-intuitive, but once this hurdle is surmounted, the wings work wonders. This allows some top-tier racing cars to corner at 4 times the force of gravity and brake somewhere in that vicinity.

However, learning to brake with downforce is a tricky proposition indeed. Because downforce builds with speed, the amount of braking pressure one can exert at speed is vastly different from when it slows to a speed under the downforce threshold. For instance, braking at high speed, say 120 mph, a driver can exert an immense amount of pressure through the pedal and the tires simply won’t lock – it doesn’t matter how many leg presses they’re capable of. However, as the car decelerates and that aerodynamic pressure is reduced, the driver has to reduce pedal pressure or they’ll lock their brakes. This is why high-downforce racers almost always lock up at the end of the braking zone these days.

 

Despite the massive tires, lockup at the end of the braking zone isn't uncommon due to the rapid change of aerodynamic grip.
Despite the massive tires, lockup at the end of the braking zone isn’t uncommon due to the rapid change of aerodynamic grip.

Coming to terms with downforce is a requisite to get anywhere in racing these days. Even club racers are employing wings and splitters to get the most out of their cars, and to find the limit with these machines, a driver must have gall and be willing to silence that voice which signals imminent death. It’s a counter-intuitive process, and requires courage to master, but once a driver can trust their car to hold on, the performance they’re capable of is astounding.

About Tommy Parry 102 Articles
Tommy Parry has been racing and writing about racing cars for the past seven years. As an automotive enthusiast from a young age, Tommy worked jobs revolving around cars throughout high school and tried his hand on the race track on his twentieth birthday. After winning his first outdoor kart race, he began working as an apprentice mechanic to amateur racers in the Bay Area to sharpen his mechanical understanding. He has worked as a trackday instructor and automotive writer since 2012 and continues to race karts, formula cars, sedans and rally cars in the San Francisco region.
Copyright © 2005-2017 RacingJunk.com All Rights Reserved.

Designated trademarks and brands are the property of their respective owners. Use of this Web site constitutes acceptance of the RacingJunk.com
Terms of Use, Classifieds Disclaimer, Privacy Policy, and Cookie Policy