This article was contributed by Henk Ormel, who has been a much beloved member of our community at Wheel Sports and an incredibly insightful eye for feedback on technical matters.
With little information to go on it is a somewhat heary topic. The principles of the fundamental working however don’t change.
To start with a little understanding of ‘ground effect’ cars. It is all about the expansion in volume that drops the pressure and creates a vacuum. This vacuum sucks the floor to the tarmac. A smaller radius makes the space between the floor and the tarmac in a shorter distance bigger. This growth in volume isn’t only the result of the increase in roof height in relation to distance (length) but also the increase in width in relation to distance. The more that volume increases, the stronger the vacuum created and the more floor downforce potential is created. With this tool in hand is is possible to calculate the desired vacuum necessary for a desired amount of downforce at a given speed. The desired top speeds on the straights are submissive to the desired top speeds in corners. The time spend driving while cornering is much much more than the time at topspeed on a straight during a GP. While overtaking in corners is much harder than overtaking on straights means a good top speed at the expense of optimum lap time has to be considered.
The design process begins with the prospected predictions of necessary downforce levels in the different corner types. Those downforce levels are a result of the prospected speeds necessary in combination with the rear wing drag and downforce in relation to the speed. In contrast to the corners on the straights there is only the downforce necessary to transfer the driving torque from the tires by friction onto the track.
So in low speed corners a car is almost exclusively leaning on mechanical grip due to lack of aero load. Every sliver of aero load that can be added is a huge benefit to the slow corner performance.
At the medium speed corners the mechanical and aero grip are both contributing to the grip. The more there is the higher the cornering speed and the earlier the driver is able to apply the power.
At high speed corners the car is almost solely depending on aeroload to make the corner. The suspension loading is one sided almost maxed out and the skid blocks are starting hitting the track.
Then the even higher speeds on the straights are arriving. At these speeds the amount of downforce generated is starting to be a problem by causing porpoising, excessive plankwear and excessive drag. Porpoising is very uncomfortable and may cause damage to driver and car components. Excessive drag is worse because you are not reaching the speeds of your competitors and get overtaken. Excessive plankwear may cause disqualification and guaranteed no points.
On the pictures taken during the Monaco GP weekend of the floors of the Williams, Mercedes and Red Bull there are striking differences and striking similarities. All floors have the strakes/floor fences mounted in a similar pattern. Behind the ending of the fences there is another blow off segment to support the created vortex by the strake outlets. All floors feature a gill-like structure on the sides of the gearbox casing. For the rest the Mercedes floor and the Williams floor are strikingly similar. Only the Red Bull floor features more gill-like structures in the roof of the venturi tunnels.
By non-linear suspension compression and damping characteristics in combination with anti-dive and -squat suspension geometry, the car is fighting the rear suspension compression with the increase in speed quite firmly. To assist this behavior those gill-like structures in the venturi tunnels are stalling specific parts of the floor at specific speeds and therefore ride heights. This drops the amount of downforce generated and therefore the suspension load. For this reason the springs can be more compliant what helps with a compliant suspension set up necessary for mechanical grip at low speeds. All the previous makes it possible to design a floor that generates way too much downforce. That means it generates more downforce at the medium corner speeds. At higher speeds the floor stalls part by part and keeps the downforce levels within reasonable limits. By stalling the floor the drag that is a byproduct of downforce disapeares together with the disappearing downforce. For this to happen predictably the floor has to sit on the predicted height at a given speed. This creates a predictable underfloor airspeed and therefore predictable stalling characteristics.
While on the photo’s the floors of the Williams and the Mercedes look similar they perform quite differently. The design speed of the Mercedes floor seems to be lower than the design speed of the Williams one. Both dump some downforce at really high speeds by the gill-like structures on the gearbox casing. The expansion under the Williams floor is less than under the Mercedes floor. Therefore the drag is less. Both use the same PU, gearbox and rear suspension. The low and medium speed performance of the Wiilams is far worse than Mercedes’ but there are not many tracks that allow for easy overtaking in corners. The Mercedes suspension seems to be quite compliant and reasonable linear. This pulls the car at speed into the tarmac and may cause excessive plankwear. This risk can be minimized by avoiding the kerbs and the most bumpy parts of the track.
Floor size matters big time. The longer the floor with a mandatory with the more area. A given vacuum acting on a bigger surface results in a greater force applied to that surface. So indeed size matters. In a way the same equation as I used at the start is valid. Start with a demand of downforce factor in expansion speeds and then you end up with an aerial demand. The width of the floor is mandatory so only the length is a variable. To meet the desired length of the floor the imaginary front axle has to shift forwards. There is a mandatory minimum measurement between the imaginary front axle and the front facing floor edge. What Mercedes did here was to lengthen the chassis to mount the front suspension further forward. This made it possible to lengthen the engine cover and the floor. A good relation between frontal area and length is advantageous for the drag coefficient and therefore for overall drag. The downside of this setup is the driver sitting further forward.
Mercedes tried the same concept as they were running from 2017 onwards. A floor as big as mandatory for the demanded downforce levels and shrinkwrap the rest as narrow as possible to reduce drag. There lies the origin of the ‘zeropod’ concept. Not the zeropods are the concept but the underlying thoughts about how to build a fast car. The zeropods are a logical result of that thought process.
Other teams with Red Bull in the lead taking a drag penalty for airstream guidance with the more bulky sidepods. This guidance is helping the floor to perform closer to its optimum. Mercedes and Ferrari still have problems with a floor riding too low to extract the maximum amount of downforce out of it to meet the demands of cornering. Mercedes misjudged the
amount of downforce needed by misjudging the lap time necessary for the W13. For the W14 the floor got extended again and the driver got shoved forwards even more. The Mercedes creates less downforce per square cm than the top competitors do . They need to compensate for that with draggy rear wing downforce.
Al parts of F1 cars are so intertwined it is very hard to discuss one part in isolation.