Why do F1 cars run flow-vis paint and aero rakes in testing?

Formula 1 teams use pre-season testing to extract as much data as possible via various methods -including flow-visualisation paint and aerodynamic rakes.

Both play a key role in every pre-season test – plus some in-season free practice sessions – as teams attempt to learn more about aerodynamic performance.

This year will be no different with F1’s 2024 pre-season test on 21-23 February at the Bahrain International Circuit, which also hosts the year’s opening grand prix on 2 March.  

Valtteri Bottas, Alfa Romeo C43, with aero paint applied

Photo by: Mark Sutton / Motorsport Images

What is flow-vis paint on an F1 car? 

Flow-vis is the brightly-coloured paint spread across an F1 car’s body part used in pre-season testing or in free practice sessions.

The paint is formed by mixing a fluorescent powder with what’s usually paraffin oil and gets applied to a certain car part when a driver is set to leave the garage. Flow-vis could be applied to a car’s front wing, its sidepod or even all over, but it is especially useful when a new body part has been applied.

Some teams may use a fluorescent paint that can only be seen under an ultraviolet light so rivals cannot look at their data, while another way to do that is by covering the car as soon as it enters the pit-lane. F1 teams must also be careful with how much flow-vis it applies because too much will cause puddles, whereas too little makes it hard for valuable data to be gathered.  

Flow-vis is used to determine aerodynamic performance because, when a car is travelling at high speeds, the paint moves across the body in accordance with the airflow. This leaves lines as the paint begins to dry, meaning it is essentially a wind tunnel but with 'real-world' air.  

Sergio Perez, Red Bull Racing RB19, rear wing detail

Photo by: Mark Sutton

How does F1 flow-vis paint get analysed?

The lines which get left behind are incredibly important because they provide greater understanding into a car’s real-world surface flow and the air’s direction, meaning teams can very clearly visualise the kind of structure that they have.

So, for example, if flow-vis is applied to the bottom of the nose then lines usually appear further up showing how air has reacted to it and the direction the nose causes air to travel.  

Once the car has returned to the garage, aerodynamicists will then take photographs before the flow-vis gets wiped off. What’s important is that the flow-vis lines are not usually visible to the naked eye and can only be analysed through images.  

When it comes down to the analysis, what teams mainly look for are any outliers in the data such as where the airflow has separated.

Airflow separation refers to when the flow of air deviates from a car’s surface and becomes turbulent leading to increased drag – as a low-pressure region has been created behind the vehicle – decreased stability and reduced downforce. This can all be observed through the flow-vis lines and that helps aerodynamicists to identify any problems, its cause and how to rectify them.  

Flow-vis paint is arguably of more importance in the modern-day F1 after the series imposed a restriction on wind-tunnel testing for 2021. So, flow-vis paint gives teams a chance to test with real air and gain greater understanding into how their car cuts through the air and where aerodynamic improvements can be made.  

McLaren MCL60 detail

Photo by: Giorgio Piola

What are aero rakes on an F1 car? 

F1 teams also use aero rakes throughout the season which are metal fence-like structures fitted onto a car during testing. Aero rakes actually come in various sizes and sometimes it’s not obvious when a team is using one, but the big ones are hard to miss as they are usually placed behind the front axle or near the rear axle.  

Aero rakes are made up of an array of Kiel probes, which paint the picture of how airflow comes off car body parts like the front wing or wheels. So, aero rakes are similar to flow-vis, except that it shows how airflow is structured on the car rather than how it comes off or around it. 

Teams are mainly looking for how the data gathered from aero rakes, which can be done almost instantaneously, measures up against what they saw in the wind tunnel.

When a car is going around the circuit, the team will measure how the metal fence bends due to the force of the air and that is used to calculate the air pressure and velocity at various points around it. 

Yuki Tsunoda, AlphaTauri AT04

Photo by: Mark Sutton / Motorsport Images

Data gathered from an aero rake then helps teams to decide on its most optimal aerodynamic setup, as it helps to create a map of the airflow around the car and shows how different setups affect the car’s performance. 

F1 teams are also looking for separation in the data, so where the flow’s separating and where the car is not getting decent flow structures - for example, if the front wing was not generating the downforce it needs to.

So, without aero rakes, F1 teams would find it incredibly difficult to judge what the optimal state is for downforce levels.

Other key terms to know for pre-season testing