Your comprehensive guide to Formula One preseason testing

Formula One is set for three days of preseason testing in Bahrain this weekend ahead of the Bahrain Grand Prix on March 28.

From Friday through to Sunday (March 12-14) F1's 10 teams will take part in the tests at the Bahrain International Circuit. The primary objective for each is to get themselves as ready for the start of the season as possible, but it always gives an opportunity to speculate on who's hot and who's not ahead of the first race.

What's different this year?

Formula One has dramatically cut the length of preseason testing in recent years. Eight days were allocated for preseason in 2019, but that was cut down to six last year. In 2020 it was held at Barcelona's Circuit de Catalunya just weeks before the COVID-19 pandemic took hold and delayed the start of the 2020 season by four months.

The pandemic is still affecting decisions 12 months later. With the first race to be held in Bahrain two weeks after testing, the location makes sense logistically, while saving costs at a time when finances have been hit hard.

It should also prove to be a cost-effective three days as the already limited track time is unlikely to be limited further by adverse weather, which can be a drawback of testing in Europe during February.

The regulations also make it easier for teams to stomach the reduced track time. The pandemic forced F1 to push back its planned overhaul of the technical regulations from 2021 to 2022 to ease costs, so for this year teams will carry over the majority of last year's car, with major non-aerodynamic changes limited under a token system.

Each team has two development tokens to spend and a shopping list of what those tokens will allow afford them to change. The only exception is for teams that buy gearbox and rear suspension parts from a rival and were already using year-old parts last season. They are allowed to upgrade from 2019-spec parts to 2020-spec parts without any token spend.

The above only applies to Aston Martin, which is supplied by Mercedes, and AlphaTauri, which is supplied by Red Bull, and only Aston Martin has made full use of the ruling.

As a result, the new AMR21 will be upgraded with Mercedes' innovative swept-back rear suspension, which was a key feature of Lewis Hamilton's title winning W11 last year, as well as a new chassis, which Aston Martin spent its tokens on. By contrast, other teams, such as Ferrari and Alpine, have had to spend their two tokens to introduce upgraded gearboxes and rear suspension.

AlphaTauri, meanwhile, decided to stick with the rear end it used last year (from Red Bull's 2019 car) as -- with the resources it had available -- it believed that was the best approach to gain the most performance over the winter.

How relevant will the times be?

At the end of each day, a timing screen will show who went fastest and slowest during that session. Inevitably, that can make it easy to jump to conclusions very early on, but the times can also be misleading.

One notorious recent example was 2019, when Ferrari left preseason looking like strong favourites based on the timesheets, only to quickly be found lacking by the time the Australian Grand Prix started two weeks later. It's not so much that the timesheets were lying on that occasion, but Mercedes introduced a major upgrade at the second test, which propelled the team onto a much steeper development curve than Ferrari that wasn't obvious based on the times alone.

That's not to say everything from testing can be completely discarded. More often than not, it is abundantly clear when a team is struggling and it also quickly becomes obvious if one team has a significant advantage over the rest.

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

Without knowledge of what each team is trying to achieve when it hits the track, it's hard to tell if a car is quick or not. Sometimes a driver will leave the garage purely to gather aero data or check systems and the resulting times will be relatively meaningless.

But with just three days of testing this year, it should quickly become clear when they are hunting from lap time and below are the two key areas to keep an eye on...

Performance runs

These are the laps when teams take some fuel out of the car and try to find one-lap performance by working through set-up changes. They are easy to spot as the drivers will alternate between 'hot laps' and 'cool-down laps', creating a tell-tale pattern of fast, slow, fast, slow on the timing screens.

Drivers have to intersperse their fast laps with slower ones to allow the tyres to recover after being pushed hard and to recharge the hybrid system, which will use up all of its battery power on a qualifying-style lap.

Tyre compounds are key to one-lap performance and Pirelli offers all five of its compounds to the teams during testing. The compounds are numbered C1, C2, C3, C4 and C5, with C1 being the hardest and C5 being the softest.

Softer rubber provides more performance, but that performance drops off at a faster rate, meaning the softest compound may only be good for a single lap before it loses its peak performance. The fastest times are likely to be set on the softest tyres in testing, but if a car using C2s is only 0.1s off a car on C5s, it's safe to assume the car on the harder compound has a significant pace advantage.

Different tyre compounds can be spotted by different sidewall markings and Pirelli provides the compound each driver used for his fastest lap at the end of the day.

The Bahrain International Circuit is particularly punishing on rear tyres, so it's possible a set of C5 tyres will struggle towards the end of a single lap, especially in the heat of the desert sun. As a result, a time set on C5s at midday is not comparable with a time set on the same compound as the sun goes down and the track gets quicker in the evening. All factors that need to be taken into account.

But even if you know the tyre compound and the time at which the lap was set, you still only know half the story. A car's fuel load is another key factor in performance and as little as 10kg adds 0.33s to a lap around the Bahrain International Circuit. Unlike tyre compounds, there is no way of knowing how much fuel a car has on board and the teams are not obliged to hand out figures.

As a result, the most impressive lap times in testing are often disguised by teams running with extra kilos of fuel in the tank, while a slower car can look surprisingly competitive by running on fumes.

Running heavy is often referred to as "sandbagging" -- F1-speak for a team hiding its performance -- but the truth is that heavier fuel loads are often used by engineers to give a more practical baseline to work from rather than to hide a car's true pace.

Unfortunately, the most useful tool to cut through the secrecy isn't available to fans and the media.

Teams closely monitor GPS traces of rival cars to gather data on both corner speeds and straight-line speed, allowing them to build a clearer picture of car performance. The speed at which a car accelerates and brakes is useful to guesstimate both its engine mode and fuel load and, at the click of a mouse, data can be cross-referenced with last year's race to identify trends and spot anomalies.

What's more, F1 teams are creatures of habit and will often stick with a set fuel load for testing from one year to the next. As staff move from team to team over seasons, it doesn't take long for an experienced engineer to build up a bank of data and knowledge to help sift through the times popping up on the timing screens and pick out the true star performers.

Race sims

One way of removing the uncertainty over fuel loads is to look out for teams attempting 'race simulations'. Typically, each driver will aim to complete at least one race simulation before going to the first race so that he can get a feel for how the car performs over a grand prix distance.

In order to complete a race distance without returning to the garage to refuel, cars will need to leave the pits at the start the run with close to the maximum fuel load of 110kg. And once we know cars are all starting out with the same fuel load to complete the same number of laps makes, it makes it much easier to compare performance.

It's not an exact science, as the time of day, track conditions and tyre strategies can skew the results, but as a general rule it is the best way to build a true picture of performance from testing.

Race sims can be easily spotted by a series of slow but steady lap times over long runs that are interspersed by race-style pit stops. Alternatively, if you spot that a driver's pit board is counting down from 57 laps (the length of a race at the Bahrain International Circuit) the chances are they are attempting a race sim.

By working out an average lap time -- removing anomalies caused by traffic or red flags from the 57 laps -- it's possible to get the best indication of how quick a car really is compared to its rivals.

Add a pinch of salt

While a clear order usually emerges from testing, it's not always representative of the first race. This year, testing and the first race are being held at the same venue, improving the chances of an accurate prediction, but even so a lot can change in two weeks.

Most teams will be looking to develop their cars rapidly at the start of this season so they can switch their focus to 2022 as early as possible. It's not unusual for teams to bring a major aero upgrade between testing and the first race and with subtle but significant changes to the aero regulations this year, there could still be a steep development curve for a number of teams.

Fortunately, we won't have long to wait between the final day of testing on Sunday and the first race two weeks later to get a clearer picture of who will be challenging for race wins regularly in 2021.

What are the rules at testing?

With the exception of passing crash tests prior to running and obeying marshal flags, there are no real rules governing testing. Running is unlimited between 9am and 6pm, although tyre allocations do put a practical limit on how many laps can be completed over the three days.

There is no scrutineering and teams could, in theory, test parts that are illegal under the regulations (although there would be little long-term advantage by doing so). In 2013, Caterham and Williams ran small bits of bodywork to divert exhaust gasses towards the diffuser which would have been illegal under the regulations but allowed them to gain a better understanding of how other teams were benefiting from doing it within the regulations.

Last year Mercedes caused a stir by trailing its innovative, but controversial, Dual Axis Steering (DAS) system during preseason. It was a system the FIA was aware of and had already moved to outlaw for 2021 but was technically still legal under the 2020 regulations. After studying its use throughout testing, rivals Red Bull protested DAS at the first race of the season in the hope of proving it was illegal (or perhaps just finding out more information about how it worked) leading to an official ruling from the FIA that it was indeed legal. Testing is often the first chance teams get to see what their rivals have built for the new season.

To use Mercedes as an example again, the world champions rolled out a 2021 car at its launch with some noticeable changes -- such as reprofiled sidepods and a bulge in the engine cover -- but technical chief James Allison said the team still had some secrets to reveal. All eyes will be on Mercedes' car to see what further innovations might be spotted when it rolls out of the garage on Friday morning.

Will the cars look different this year?

You'll have to look pretty carefully at photos to spot major changes, but once you know where to look you'll see some very obvious development areas.

The FIA has made changes to this year's aerodynamic regulations to reduce downforce and slow the cars. There were concerns last year that the cornering loads being generated were putting dangerous forces through the structure of Pirelli's tyres, leading to failures at the British Grand Prix and reliability concerns at a number of other races.

As a result, changes have been made to the regulations dictating the shape of the floor, details on the rear brake ducts and the length of strakes on the diffuser to cut downforce. On their own each change would be relatively minor, but if you were to crudely apply all of them to a 2020 car they would cut downforce levels back to the loads seen at the start of 2019 -- effectively wiping away two years of performance development.

Actual downforce levels are likely to be much closer to the 2020 cars, as the teams have had time to optimise their aero packages around the new rules over the winter. Key performance areas will be the floor itself, which now tapers inwards when viewed from above, limiting the downforce it can create and making it harder to manage the airflow around the sensitive area ahead of the rear tyres.

Teams have been very coy in showing details of this area during the launches, with Red Bull only releasing front-on images of what appeared to be a very underdeveloped car and Mercedes putting a dummy floor on the W12 during its launch.

But the aerodynamics at the rear of the car do not work in isolation from the front, and changes upstream are also expected, especially around the bargeboards -- between the front wheel and the start of the floor -- to manipulate the airflow rushing rearwards. This will be another key area of development for teams this year.

Has anything else changed?

Arguably the most important change for 2021 is to the tyres. The four lumps of rubber at each corner of the car may not be the most exciting things to analyse, but they are solely responsible for transmitting the performance of the car to the road.

It seems Pirelli was not convinced that downforce cuts alone would protect their tyres and it has responded by beefing up the construction of the tyres for the new season. Last year's Pirellis were already a carryover from 2019 (a decision made when F1 was still expecting a switch to low profile tyres in 2021 rather than 2022) so were never really designed for the downforce loads seen last year.

The hardier construction for 2021 is 2.5kg heavier per set and roughly a second per lap slower in terms of performance. Unsurprisingly, that combination led to criticism from drivers when they first tested the tyres last year, but it should be remembered that they were testing them with a car optimised around a different tyre construction, which resulted in a handling imbalance.

Dialing the balance back to the sweetspot they know and love will be one of the main targets for all drivers over the next three days, while understanding how the new tyres perform over a race distance will be key for all teams ahead of the first race.