RAKE ANGLE
The RAKE of an F1 car is the amount that the rear of the car is higher than the front of the car. The RAKE ANGLE is this angle relative to the horizontal. You may see on TV where it looks like the car is raised at the back producing a visible upwards slope of the entire chassis. This page will explain why some teams decide to do this and why some teams prefer not to.
F1 cars nowadays have a rake angle of between 1 and 2 degrees. This may not sound like a large amount but the effects can be extreme. A few millimetres of height difference can have great aerodynamic effects on the car.
Adrian Newey, the legendary F1 designer and engineer was the first to pioneer the high rake car properly on the Red Bull early last decade. This is the design that took Red Bull to 4 straight world championships and nowadays most of the grid employ this philosophy. However, notably, Mercedes have always opted for a low rake car and could this be the reason they are able to dominate across the whole season. They have, after all, won 6 (nearly 7) championships in a row. Let's break down why.
In a nutshell the high rake philosophy we see on the current Red Bull, AlphaTauri and Renault allows the car to reach higher peak downforce. The low rake of the Mercedes does not reach the levels of peak downforce but is more aero efficient. Think of the entire car as one big wing and you will understand that high rake allows a larger volume diffuser and more prominent rear wing system. However, the low rake is more streamlined as the car is lower to the ground (i.e. less extreme angle of attack). This is why Mercedes tend to dominate at tracks such as Silverstone, Barcelona, Spa and Monza where more emphasis is placed on lower overall drag and the power unit strength. This is also why we see them 'struggle' more at tracks such as Monaco, Singapore and Mexico where peak downforce is most important.
High Rake V.S. Low Rake
The technical explanation for the differing rake ideas is this. A high rake design increases the size of the diffuser so at low speed you can get the maximum amount of mass flow of air running underneath the car to give you the most downforce possible. A high rake car also has an advantage when it comes to managing rear tyre wake which is the messy turbulent air that exits the back of the rear tyres. This wake can sometimes obstruct the air exiting the diffuser which we want to maximise. To combat this vortices are produced and sent towards the tyre to prevent airflow separation and encourages the air to stay attached to the tyre. This results in a smaller wake and less drag. If the car is high rake then small movements of the tyre won't make a big difference in the distance between the tyre and the floor but this is more pronounced on a low rake car. Therefore aero devices (the ones generating the vortices) have to be designed more thoroughly to allow for the small up and down movements.
However, with a low rake design the floor is much closer to the ground and due to this reduced volume, air can travel much faster through it (Venturi Effect). this decreases the pressure an gives more downforce. See this page for a more detailed explanation. But, this effect works better in medium to high speed corners as this is where air travels much faster through the diffuser. Low rake also seals the floor better; it stops the air from coming out the sides from under the floor. If the floor is not 'sealed' then you won't get the same pressure difference as the air acceleration is impeded.
Some other reasons to opt for low rake is that the centre of gravity is lower and this helps with overall stability and tyre management.
Whichever way you choose to go in terms of rake, it is a very important decision. You cannot change the rake overnight as many other components need to be designed with the rake setup in mind. For example, the front and rear wing will be closer or further from the ground, the front and rear suspension will be different. Even out-of-the-way aero bits like bargeboards will be affected
Rake & Wheelbase
Rake is also explicitly linked to the wheelbase of the car. We now know that a higher rake car produces more downforce because of the extra space between the floor and the track. To be technical, the downforce created is a function of the negative air pressure multiplied by the area that the pressure is acting on (basically the area of the floor). Therefore, for a low rake car to try and get the equivalent downforce of a high rake car, it needs to have a bigger floor.
And guess what, the low rake Mercedes car (1.2 deg rake angle) has a much longer wheelbase than both the Ferrari (1.5 deg) and Red Bull (1.9 deg) especially. The Mercedes is 5% or 19 cm longer than the Red Bull.
This does make the car heavier as there is just more car but is this worth it for the added aero efficiency and stability/ Mercedes certainly think so and it's definitely working considering their domination over the last few years!
If you were an F1 engineer which option would you go with regarding rake?? Let us know here! Tell us why