The 0.759% shift that created F1 2021's thriller 

No one knew it at the time, but the pattern of the 2021 Formula 1 title battle was set way back in the pandemic spring and summer of 2020. As the world shut down, teams and rule-makers worked in something close to panic to keep the world championship afloat. Among the raft of changes decided upon was to use the same cars for two seasons, with only limited changes allowed.

To keep a lid on speeds, because of concerns about tyre integrity, parts of the aerodynamic surfaces at the back of the car were cut away. These changes – initially apparently small and relatively inconsequential – were the biggest single factor behind a season of Mercedes domination in 2020 turning into one of the 
most intense and closely fought campaigns in history the year after.

From the moment the cars hit the track in pre-season testing, the effect was immediate and obvious. The Red Bull looked fast and planted in Max Verstappen’s hands, while the Mercedes was nervy and skittish, Lewis Hamilton and team-mate Valtteri Bottas suffering a number
 of spins as they struggled to get a time out
 of their revised car. And when Verstappen put the Red Bull on pole for the season-opening race in Bahrain by nearly 0.4 seconds, the impression that Mercedes had a fight on its hands was confirmed.

That first race set the tone for the season. 
The Mercedes was much closer to the Red Bull on race pace than in qualifying. Hamilton got 
the jump on Verstappen with an early stop,
and the race distilled to a gripping climax,
with Verstappen closing on Hamilton on better tyres. They went wheel to wheel. This time, Hamilton came off best, and Mercedes grabbed an unlikely first win.

The opening four races gave a somewhat inaccurate impression of reality, for Hamilton won three of them. Verstappen’s only victory 
was in the wet-dry race at Imola, where Hamilton was lucky to get away with going off and losing a lap mid-race. He was saved by a red flag caused by the crash between his team-mate and the Williams of George Russell, and he recovered to finish second.

Those results were down to a number of factors – a couple of minor qualifying errors 
by Verstappen, and circuit characteristics favouring Mercedes slightly in Portimao and Barcelona, where Hamilton put in two of his
best drives of the season.

Hamilton won three of the first four races, passing Verstappen late on to take victory in Spain

Photo by: Steven Tee / Motorsport Images

But from Monaco on, the true picture of performance emerged. Red Bull went on a run of five consecutive victories. Verstappen, who would have won all five were it not for a tyre failure in Azerbaijan, established a commanding championship lead, and from then on it was all about catch-up for Hamilton and Mercedes.

It looked all but over for Hamilton, until a big upgrade package introduced at Silverstone made the Mercedes inherently a faster car than the Red Bull. But it gave up its secrets reluctantly and for quite a while the team struggled to maximise it.

There was a strategy error at the restart in Hungary, leaving Hamilton the only car on the grid for one of the most bizarre opening sequences in F1 history, and consigning him to a fightback from last after one lap. Then there was the race that wasn’t a race in Belgium, and Verstappen took Hamilton out in Monza.

Mercedes suspects the changes were deliberately planned to peg it back; the FIA and F1 say it was nothing of the sort. Whether by subterfuge or serendipity, they disproportionately affected the cars designed to run with low rake compared with those running high rake

After languishing in seventh for most of the race in Russia, Verstappen was saved by the late downpour and vaulted to second. An engine penalty hamstrung Hamilton in Turkey then in Austin, against expectations, the Red Bull was a slightly quicker car.

In Mexico, as expected, Verstappen won decisively, helped on his way by Bottas leaving a gap the size of a barn door on his outside on the run to the first corner, after tyre-temperature struggles in qualifying had relegated Verstappen to third on the grid. All of that left Hamilton realistically needing 
to win the final four races of the season to take the title. He very nearly did it too.

With a change in set-up approach for Brazil, Mercedes could finally access all the car’s performance and Hamilton went on a roll, only to be undone on the very last lap of the final race after the race director made up the rules as he went along.

It was 22 races over nine months that was at various turns breathless, thrilling, bad-tempered, toxic, gripping and, of course, controversial.
 At the heart of it were two of the finest drivers who ever walked the earth. They raised themselves head and shoulders – and more – above the rest of the field.

Hamilton congratulates Verstappen after his last-gasp defeat in the controversial Abu Dhabi finale

Photo by: Steven Tee / Motorsport Images

The technical backdrop

How did a season in which Hamilton won 11 of the 17 races and Verstappen only two turn into one of the closest in history while using the same cars? The answer lies in the detail of those changes dreamed up in the summer of 2020. 
A triangular section – known as the ‘cheese slice’ – was cut out of the floor in front of the rear tyres, and some of the aerodynamic appendages at the back were removed.

Mercedes suspects the changes were deliberately planned to peg it back; the FIA and F1 say it was nothing of the sort. Whether by subterfuge or serendipity, they disproportionately affected the cars designed to run with low rake compared with those running high rake. Mercedes and Red Bull are the originators of those contrasting design approaches.

Mercedes runs low rake – a flatter angle from front to rear – using a long wheelbase with a large floor area to generate downforce. Red Bull draws its cars with a high rake – a steeper angle from front to rear – and the greater height of the diffuser is the key aerodynamic factor.

Why did the changes affect Mercedes more than Red Bull? The answer lies in something called tyre squirt – disturbed airflow generated by the rear tyres – which spills into the diffuser area. Tyre squirt creates slow, turbulent air in an area where teams want clean, fast airflow to generate the low pressure that sucks the rear of the car towards the ground. So teams work hard to get it out of the way.

On a high-rake car, this is done by the fences in the diffuser and the high volume of air working together to create out-wash, which sweeps the tyre squirt out of the diffuser. But a low-rake car does not have the same air mass in the diffuser. It attacks tyre squirt at source.

The floor edge, close to the ground, generates vortices – mini-tornadoes – which are directed down towards the inner edge of the tyre to deal with the squirt. Removing the ‘cheese slice’ makes it harder to generate those vortices, so more disturbed air leaks into the diffuser space, creating a loss of downforce
 and greater instability.

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On certain types of circuit this problem was less pronounced – hence the Mercedes’ stronger performance in Portimao and Barcelona – but the problem was never fully sorted until Mercedes’ Silverstone upgrade.

Silverstone upgrade helped Hamilton to a significant win in the title race, albeit only after a controversial clash with Verstappen

Photo by: Charles Coates / Motorsport Images

How much of a performance difference did this make? In 2020, Mercedes’ average margin over Red Bull in qualifying was 0.77%. From 2020 to 2021, Mercedes lost 1.663% of performance on tracks that hosted races both years, Red Bull only 0.904%. Year to year, Mercedes lost 0.759% more pace than Red Bull. In other words, nearly all its 2020 performance advantage.

Red Bull would argue that it adapted better to the changes – Verstappen described the progress it made as a team as “very impressive”. Mercedes would counter that the nature of the changes made it harder to find the normal gains – Hamilton, echoing and enhancing team boss Toto Wolff’s description of the difficulty of getting Merc’s 2017 car into its set-up sweet spot, described the 2021 machine as “a monster of a diva”.

Inevitably in a season so close, results swung on tiny margins. In Portimao qualifying Verstappen ran fractionally wide on a lap that would have put him on pole, and had the time disallowed. Had he started at the front, could he have held on to win? 

There were other factors at play, of course. Honda upped its game, bringing forward by a year an engine upgrade it had planned for 2022 after the board’s decision to quit F1. Red Bull also benefited in the first half of 2021 from using a flexible rear wing which bent backwards on the straights, reducing drag. This circumvention of the intent of the rules was ended by a stiffening of load tests from the French Grand Prix.

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That, combined with Mercedes’ Silverstone upgrade, meant Red Bull went from having a small advantage on the straights in the first
half of the season, to a less-small deficit in the second. Meanwhile, Mercedes’s attempts to recover the gap were hampered by an engine reliability issue which raised its head in the second half of the season.

The driver face-off 

The effect of all this was to produce two cars very closely matched in performance, between which the advantage swung from race to race depending on a number of factors.

How close was it? Over the first half of the season, the Red Bull was the faster car in qualifying by an average margin of 0.014s;
 over the second, it was the Mercedes, by 0.167s, which comes down to 0.123s if you adjust for Verstappen completing the spectacular qualifying lap which he ended in 
the wall at the final corner in Saudi Arabia.

Inevitably in a season so close, results swung on tiny margins. In Portimao qualifying Verstappen ran fractionally wide on a lap that would have put him on pole, and had the time disallowed. Had he started at the front, could he have held on to win? Quite possibly.

Verstappen breaching track limits on a Portimao qualifying lap that would have given him pole was one of the many small moments that had big consequences in 2021

Photo by: Mark Sutton / Motorsport Images

In Baku, a tyre failure – caused, Pirelli said, by the tyres being run below expected minimum pressures – cost Verstappen a win. Hamilton was then poised to take the lead at the restart, only to inadvertently knock the ‘brake magic’ button – which turns the brake bias all 
the way to the front so as to increase tyre temperatures on a warm-up lap – on the run to 
the first corner, where 
he locked up and sailed into the run-off area. 
No points, when he
 could have had 25.

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In France, a strategic miscalculation by Mercedes turned a Hamilton lead into a Verstappen victory. Then in Belgium, on a low-downforce set-up in the wet, Hamilton was a touch over-cautious through Eau Rouge in qualifying, and he lined up third, when he could have been on pole. On a weekend when there was no race, but half points were awarded, that was another points swing.

With the two cars and drivers evenly matched, the season was defined by a series of hard-fought and incredibly close on-track battles. Races were often decided on strategy, But when the two
 cars battled together on track – as they did at Bahrain, Imola, Barcelona, Silverstone, Monza, Austin, Interlagos, Jeddah and Yas Marina – there were inevitable fireworks.

At the starts in Imola and Spain, Hamilton backed out when Verstappen took what was to become his familiar approach – on the inside, throw the car in, leave the guy on the outside a choice whether to avoid him, often by going off track, or crash, sort it out on the exit.

Hamilton started the British Grand Prix with a 33-point deficit, and decided enough was enough. After a frantic half-lap’s battling the two collided at Copse, Hamilton – alongside on entry – deciding the time for backing out was over. Verstappen ended up in hospital, via the tyre wall, unimpressed; Hamilton the winner, despite a 10-second penalty after being found predominantly to blame for the accident.

That incident coloured the rest of the season. At Monza there were two flashpoints. Hamilton backed out on the first lap, from the outside of the Roggia chicane. But not mid-race at the Rettifilio, where they collided again, and Verstappen’s car ended up on top of Hamilton’s. This time Verstappen was penalised.

Then, in Brazil, many felt that Verstappen over-stepped the line. This was Hamilton’s day of days – in 2021, and perhaps in his entire career. Relegated to the back of the grid for the sprint qualifying event, Hamilton finished it fifth in just 24 laps. Dropped to 10th for the start of the grand prix, he was third behind the Red Bulls of Verstappen and Sergio Perez within five laps.

Monza clash for which Verstappen was penalised was one of many flash points between the pair in 2021

Photo by: Jerry Andre / Motorsport Images

The second part of the race, after a safety car, was all about Hamilton tracking Verstappen and trying to find way by. On lap 48, he thought he’d done it. He got a run on Verstappen and was ahead on the outside into Turn 4, the Descida do Lago. Verstappen went in deep and fast, on a trajectory and speed that would never have kept him on track. Both cars went off, but the stewards declined to investigate, to the incredulity of 
many other drivers.

At a meeting at the next race in Qatar, the drivers demanded a clear explanation of what was allowed in wheel-to-wheel racing. They didn’t get one. At the race after that, in Jeddah, Verstappen and Hamilton were at it again.
 And this time Verstappen did get a penalty.

At the final race in Abu Dhabi, Verstappen was again on the wrong side of a decision, this time adjudged to have forced Hamilton off track as he attempted to retake the lead on the first lap having lost it at the start. The race director decided Hamilton did not have to give up the lead, despite having gone through the run-off area and cut the chicane.

Verstappen felt none of this was fair,
 that his driving was hard but acceptable.
Others disagreed.
 But all year, there 
were complaints about
 an inconsistency of decision-making from officials; the incidents between Hamilton and Verstappen were just the tip of the iceberg.

In the end, Verstappen won 10 races to Hamilton’s eight, led well over twice as many laps and took 10 poles to Hamilton’s five. Hamilton would argue
 that the victory tally should have been nine-nine had it not been for the race director’s improvisation with the rules in Abu Dhabi. 
But Verstappen was, by any measure, a worthy and deserving champion.

Every race he finished, bar Hungary, he was either first or second. As Mercedes turned the screw in the latter stages of the season, Verstappen, as Red Bull team boss Christian Horner said, kept Red Bull in it. The Dutchman's drive in Austin, in particular, was a masterpiece of maturity and control, of the sort Hamilton himself has produced many a time over the years.

Hamilton was on course for the title in Abu Dhabi until the controversial late restart

Photo by: Zak Mauger / Motorsport Images

And then there was the qualifying lap that nearly was in Jeddah. Fernando Alonso was watching it live in the TV pen, hugely impressed, and then clearly disappointed when it ended in the wall. “Max is driving – in my opinion – one step ahead of all of us,” Alonso said later.
 And when Verstappen set pole by nearly 0.4s in Abu Dhabi, there was more praise: “Unbelievable. Honestly unbelievable. He’s outstanding.”

The consistently high level of Verstappen’s performances in 2021 surpassed even Hamilton, who had a handful of lukewarm moments. He got away with the error in Imola, which could have been very costly. He was weak in Monaco. He didn’t view the ‘brake magic’ incident in Baku as a driver error per se – justifiably – but an error it was nevertheless.

But arguably Hamilton’s highs were even higher than Verstappen’s. His win in Brazil was undoubtedly the drive of the season – making up an effective 25-place grid penalty to come through the field twice to win – and will go down as one of his greatest ever, if not the very best.

When he needed to win all four races at the end of the season, he was on course to do it – despite having to pass Verstappen on track in three of them, knowing that an incident would effectively end his hopes. And the way he dealt with Verstappen’s aggression in wheel-to-wheel racing was pretty much flawless, Silverstone notwithstanding. How many other drivers could have handled Verstappen with so much control?

Amid all this quality it was a shame that, after arguably the greatest F1 season ever, between two such outstanding drivers, the FIA managed to find a way to end the championship in the most unsatisfactory way: decisions by the race director, taken apparently contrary to the rules, decided who won the title.

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It might not have produced the wrong champion – when Verstappen and Hamilton were as good as they were in 2021, there could have been no such thing. But it certainly left F1 with some soul-searching to do before it embarks on a new era that has a lot to live up to after such a spectacular end to the last one.

Andrew Benson is BBC Sport's chief F1 writer

Verstappen was crowned champion, but the title race could have gone either way

Photo by: Erik Junius