Bottom plate and diffuser Secret - Change diffuser first change spring stiffness?

Operating principle of baseplate and diffuser

Baseboards and diffusers are becoming more and more popular with fleets and refit enthusiasts because their installation process is relatively simple, so whether they actually increase downforce after loading the car or not, now basically belong to the standard equipment of a human hand. The principle of the diffuser is simple: When we force the space for air flow between the floor and the floor of the vehicle, the air from the front of the vehicle into the floor must accelerate through the space between the floor and the floor. Therefore, if the bottom plate is made as flat and smooth as possible, the effect of accelerating the above air at the bottom of the vehicle can be enhanced.

Wood is a good material to use as a base plate because it is cheap, easy to work with, and also more resilient to support the bottom, which can better withstand impact. According to the Venturi effect, the airflow accelerated through the floor can create downforce. In the front lip of the vehicle, we often see a "reverse tail" design, that is, the bottom plate is raised in an upward arc. The Formula 1 cars of 2023 have this design very clearly. When the air flow enters the floor from the front lip, due to the action of resistance, the air flow rate will be slower and slower. Therefore, there will be an upward opening shape similar to the front lip at the rear of the car, which increases the air flow rate and further enhances the effect of "sucking" the car on the ground. However, if the rear diffuser is raised too much, it will cause the air to peel off, and the downforce will drop instantaneously.

We also see dramatic side skirts on some cars to keep the air from leaking out of the sides, but not all races allow them. The Porsche 919 Hybrid EVO, which produced the fastest lap at Newnorth, is not subject to the rules of the race and therefore uses all the air kits that create maximum downforce.

At the same time, in order to make the air flow under the car stable to the rear diffuser, the car bottom will be designed with a number of longitudinal fins, so as to sort out the air flow. But these fins, which are about 5mm thick, also take up space in the diffuser channel. The thickness of the 6 longitudinal fins is about 30mm, which is equivalent to 3% of the space for a diffuser with a width of, say, 1m. This 3% reduction in diffuser area is not a negligible amount if we want to find the last 0.1 seconds of lift space in the vehicle with the new air force kit. Therefore, do not build too many channels in the diffuser. Five channels is generally enough to comb the airflow, and the number of diffuser channels in the rear of a Mercedes SLR looks extreme.

One problem with powerful diffusers is the distance over which the spring compresses. Due to the strong downforce at high speed, the spring of the rear axle may be strongly compressed and the height of the body will be greatly reduced. In the curve, the height of the body on the outside will be further decreased with the rolling of the vehicle, resulting in the bottom support and even the loss of control of the vehicle. For example, in the just ended F1 race in Bahrain, McLaren and Ferrari drivers each had a spin out of control in Turn 9. The reason was that the height of the car body dropped sharply under the action of strong downforce. After encountering bumps on the track in the corner, the chassis was heavily backed up and suddenly lost grip, resulting in loss of control. Therefore, the setting of spring stiffness and body height also needs to be carefully calculated and adjusted with the lower pressure of the vehicle. Too low body height may even lead to serious accidents.

Design philosophy and guidelines

 Air should pass through the floor as laminar as possible to minimize turbulence.

 Any openings in the floor surface, such as components for heat dissipation and ventilation, exhaust components, etc., will offset a portion of the downforce generated by the floor, thereby reducing grip.

 The bottom plate should not have any convex shape toward the ground. It should be flat or even sunken as far as possible, so as to generate as much negative pressure as possible.

 Concave front axle, i.e. upturned shape can increase downforce

The point at which the tail diffuser begins to tilt upward should be from the rear axle, thus precisely increasing the downforce on the rear axle. At the same time, the side skirt should be designed according to the competition rules to ensure that the air inside the bottom plate does not leak out as far as possible. The Angle at which the diffuser ends up depends on the track characteristics. For a medium-speed track, such as Newnorth, the diffuser Angle is about 7 degrees. The upswing Angle needs to be achieved in order to generate optimum downforce at the upswing starting point, which should be precisely located at the rear axle of the diffuser.

The correct tail Angle helps the diffuser to work better. The correctly positioned tail with its correctly calibrated fin Angle can help the diffuser suck the vehicle to the ground.