F1 testing: What preseason in Bahrain will reveal about 2025

Preseason testing is something of an enigma in Formula 1. Fans always get excited to see new cars onthe track, but with no competitive element to a test day, the lap times are relatively meaningless.

So, what will the teams really get up to over the three days in Bahrain? And is there anything we can glean from the timesheets at the end of the week?

Why do F1 teams go testing?

Although F1 cars are meticulously engineered, they still amount to 200 mph science experiments when they first hit the track in testing. Up until the moment the car leaves the garage, its performance has only ever existed in a semi-virtual world of simulations and wind tunnel tests back at the factory. Worryingly for teams, the results in the real world can sometimes be quite different.

During preseason testing, F1 teams go through a rigorous debugging and refining process to make sure their cars are as fast and reliable as they can be when racing begins in Australia on March 16. In the past this process was spread over 10 days or more, but to cut costs, the number of days on track before the first race has been reduced to three in recent years.

The opening morning of testing is usually spent running systems checks on the car to make sure everything is operating as it should. Although teams have advanced test benches at their factories and will likely have completed a 200-kilometre shakedown prior to official testing, nothing compares to running the car in the heat of the Bahrain desert. Checks on the cooling system, hydraulic system and electrical system are crucial to flush out any reliability issues early on.

In its race specification, an F1 car carries more than 300 sensors creating up to 90 megabytes of data per lap, but in testing those numbers are even higher to harvest as much real-world data as possible. Sensors on F1 cars are sometimes too small to spot and are often kept under the bodywork to measure temperature, inertia and loads -- but when it comes to understanding a car's aerodynamics, the sensors are often impossible to miss.

Big metal fences known as rakes are attached to the cars behind sensitive areas of airflow to measure air pressure and understand the flow structures around the car. The rakes are made up of a series of pitot tubes, which measure airspeed, and their readings are compared with the work the teams have conducted over the winter in the wind tunnel and via computational fluid dynamics (CFD). If the real-world data matches up with the simulations, a team is already several steps closer to extracting the true potential of the car at the first race. If it doesn't, the team is already on the back foot.

Another method for understanding real-world airflow is to douse the car in "flow-vis" paint and see how the colourful, water-based liquid spreads across the bodywork at speed. This surprisingly simple method allows engineers to see if the aerodynamic surfaces are having their intended impact on the airflow.

Feedback from the driver is another key tool for understanding a new car. Steering feedback and brake feel are also early boxes to tick, although it can take more than half a season before a driver is truly happy with the finer details. Drivers can also help engineers understand where lap time is leaking away by describing the behaviour of the car at various stages of different corner types.

Once it's been established that the fundamentals of the car are operating as they should, teams turn their attention to setup. Finding the right setup is crucial to unlocking performance, and this process will take up the vast majority of the three days of testing.

Knowing how a car will react to different ride heights, wing angles and suspension settings helps the team build up a toolbox of solutions to exploit in different situations later in the season. Engineers will spend large parts of testing conducting "sweeps" through different setup combinations to find out what works and what doesn't across different fuel loads and tyre compounds. Gaining as much knowledge as possible at this stage of the year can pay dividends later in the season when handling issues appear in the heat of competition.

A reliable car that responds well to setup changes is the aim by the final day of preseason, along with reams of data to inform the next steps of car development back at the factory.

How to spot who's quick and who's not

The lap times as they appear on the timing screens rarely present an accurate picture of the competitive order. A light fuel load and a fresh set of soft tyres can make a distinctly average car look faster than the most competitive car on high fuel and used hard tyres. As a result, the order at the end of each day can be misleading.

Tyre compounds are key to one-lap performance in testing. Pirelli's compounds are numbered C1, C2, C3, C4, C5 and C6, with C1 being the hardest compound and C6 -- a new compound for use at street races this year -- being the softest. Softer rubber provides more chemical grip and performance but is less durable over several laps. The fastest times in testing are usually set on softer-compound tyres, but if a car using C2s is only a tenth of a second slower than a car on C5s, it's likely the car on the harder compound has an underlying pace advantage.

Temperatures also fluctuate throughout the day, with Bahrain offering its optimum track conditions once the sun has set and the tarmac has cooled. As a result, a time set on C5s in the heat of the midday sun is not comparable with a time set on the same compound under the floodlights late in the day.

A car's fuel load is also a major factor in performance, and as much as 10 kilograms will add roughly 0.3 seconds of lap time. Put another way, a car with a full tank at the Bahrain International Circuit can be as much as 3.5 seconds per lap slower than when it's running with just enough fuel for a single lap.

From the outside, there is no way of knowing how much fuel a car has on board, and teams are not obliged to let anyone know. As a result, the most impressive lap time in testing might be set by a team running with 60 kilograms of fuel in the tank, while a fundamentally slower car can look surprisingly competitive by running with 10 kilograms on the same tyres at the same time of the day.

Loading the car with fuel during testing is often referred to as "sandbagging" -- F1 lingo for a team intentionally hiding its performance -- but the truth is that a fuel load between 60 kilograms and 30 kilograms offers a more practical baseline for understanding car performance.

Despite the fastest times painting an unreliable picture, it is still possible to piece together who's quick and who's not by digging deeper into the available data. By recognising certain patterns in the lap times, it's possible to gain a better understanding of what's really going on and start to make predictions about who has found the biggest step in performance over the winter.

One way of removing the uncertainty over fuel loads is to look for teams attempting race simulations. Most teams will aim to do one by the end of the three days so that they can gain an understanding of how the car performs over a grand prix distance as fuel levels go down and tyre wear sets in.

In order to complete a race distance without returning to the garage to refuel, cars will need to leave the pits at the start of the run with close to the maximum fuel load of 110 kilograms. These race simulations can be identified by picking out 57-lap stints in the timing data. Once we know cars are starting out with the same fuel load to complete the same number of laps, it makes it much easier to compare performance.

It's not an exact science because the time of day, track conditions, engine modes and tyre strategies can skew the results, but as a general rule, it is the best way to build a more accurate picture of performance by removing some of the questions over fuel load.

While some kind of order usually emerges from testing, it's not always representative of the first race. A car that's quick at the Bahrain International Circuit -- a track that rewards good traction, braking stability and low rear tyre degradation -- might not be as competitive at Melbourne's Albert Park, which has a smoother track surface, different corner profiles and a more unpredictable climate.

What's more, teams will look to develop their cars as much as possible between the first test and the first race, with upgrade packages already being worked on for the opening few races. A car that starts slowly in testing might also be a few setup changes away from unlocking significantly more pace, and the key to that performance might only present itself after test data has been fully analysed back at the factory.