Why ground effect has revolutionized motorsport

Technical revolutions spark all the time from motorsport engineers, always pushing the boundaries of human knowledge to honor the “Go faster” motto. In this particular case, aerodynamics has been a colossal area of study. From aerodynamics, the concept of downforce gained a lot of influence in F1’s design when Colin Chapman started putting airfoils on his Lotus 49C, as for it augmented the car’s grip without adding weight. In this aspect, ground effect is an excellent way of obtaining downforce. The earliest studies of ground effect include Jim Hall and the famously polemic Chaparral 2J, a.k.a “Sucker Car” and its purpose-installed fans for “sucking” the air from beneath the car and huge side skirts, creating humongous amunts of downforce, leading to the quick ban of active aero devices (boo!). The Brabham BT46B also featured a fan for “cooling” which made the same principle and was banned as well. Colin Chapman (Always him) was also doing some investigations on the matter, partnered with a UC Berkeley researcher to investigate ground effect in an Indy 500 challenger, using a venturi shape (pictured below) to speed up the air, and generate downforce.If you recall Benoulli’s principle, pressure is inversely proportional to fluid speed. Increase flow speed and pressure drops and vice-versa. Thus, the car would have low pressure underneath the car and more downforce.

This concept returned in 1977 with the Lotus 78. It featured very large sideskirts to isolate the venturi from the atmosphere and these enormous inverted airfoil-like shapes inside the skirts. Again, this sped up the air passing beneath and created downforce without any active devices. The car proved to be a success, earning Lotus the 1978 driver’s and constructurs championship with Mario Andretti. Ground effect remained as the future of F1, with some examples of the early 1980’s featuring no front wings at all, such as the Brabham BT53, which raced withouth the front wing at times. Porsche also made similar efforts with the 962 multiple Le Mans winner, who started the trend on endurance and GT cars. As motorsport progressed, most, if not all cars feature rear diffusers, which are small venturis installed in the rear only due to regulations.
However, as it was used, the gigantic venturis generated 40 % more downforce. You heared right. The lotus 78 made about 40% more downforce than any other F1 car on the grid. This was why it won 9 out of 15 races it disputed. The car had so much downforce that Mario Andretti described the car as being “Planted on the ground”.

Sadly, these ground effect cars were banned in F1 in 1983 and ground effect was restricted to the rear diffuser. However, there was a very good reason: if the car faced a bump and one side stood higer from the ground, the car would flip sideways, leading to horrendous crashes. A real shame.
Nonetheless, it is still a great part of a race car’s aerodynamics and can make a difference, such as when BrawnGP used its famed double diffuser for the 2009 F1 season. Still, almost every form of motorsport uses a rear diffuser somehow, especially Indycars. It accounts for about 30% of a racecar’s downforce and can make a difference between a winning car and the car that could be. When Chapman introduced the Lotus 78, he changed forever the way engineers would design cars forever.

Also, high-performance cars feature rear diffusers and ground effect trickery, such as the McLaren P1. If you look at the rear, you will clearly see the tunnels opening from the undertray. Another very good example of F1 tech coming to street cars. Not only do supercars have ground effect devices, but also other simpler cars, such as the Subaru BRZ feature this as well. All for that lovely and precious downforce so you can carve through the curves like a F1 champ.

Hope you enjoyed! What do you think of ground effect? Is it a revolution, yay or nay? Would you put a rear diffuser on your car? Share your opinions on the comments!