F1's Deflate-gate explained: Why stewards cleared Mercedes in Italy

Lewis Hamilton

What was wrong with Hamilton's tyre pressures?

The left-rear soft tyre on Lewis Hamilton's Mercedes on the grid was found to be 0.3 PSI below the minimum tyre starting pressure specified by Pirelli for the Italian GP, while the discrepancy on Nico Rosberg's was 1.1PSI. F1's tyre supplier had prescribed a minimum of 19.5 PSI for the rear tyres (which is enforced by the rules) in the wake of the two high-speed blowouts at the previous race in Belgium.

But the team were later cleared of any wrongdoing. So what happened?

Nearly three hours after news first broke that Mercedes were under investigation, the stewards ruled that 'no further action was required' and Hamilton's Monza win stood. The devil, as ever, was in the detail.

Having heard representations from Mercedes' senior technical figures – led by Paddy Lowe – the stewards were happy that 'the pressure in the tyres concerned were at the minimum start pressure recommended by Pirelli when they were fitted to the car'. 

Stewards also found that Mercedes' engineers had, as is standard procedure, disconnected the tyre blankets from their power source and the 'tyres were significantly below the maximum permitted tyre blanket temperature at the time of FIA's measurement on the grid'. Crucially, Mercedes were found to have followed the correct procedure ahead of the race 'for the safe operation of the tyres'.

The Sky Sports F1 team analyse the stewards decision to clear Mercedes of any wrongdoing during the Italian GP.

So there weren't any deliberate shenanigans going on?

Mercedes boss Toto Wolff was adamant that the team had followed the usual procedures agreed with Pirelli in attendance when the tyre blankets were prepared and pressure measurements were taken ahead of the race. He also gave short-shrift to any suggestion that Mercedes had somehow deliberately set out to reduce the pressures once the tyre temperatures had gone down: "After Spa we have been working very intensely with Pirelli to make these tyres safe - and now we should do something so ridiculous?" said the Merc chief.

Moreover, with such a speed advantage around Monza on race-day - Hamilton was routinely over half-a-second-a-lap quicker than nearest pursuer Sebastian Vettel - and large leads in both championships, why would they?

When were Mercedes told they were under investigation?

Mercedes were first alerted to the alleged breach towards the end of the race when a notice from FIA technical delegate Jo Bauer, concluding with the formal declaration that the issue had been passed on to the stewards, declared that the 'starting pressures' on the left-rear tyres of Rosberg and Hamilton's cars had been found outside of the prescribed limit. The time-stamp on the notice was 15:04 – approximately fifteen minutes before the end of the race.

And that's why they didn't pump them up on the grid?

Correct! Mercedes insisted the tyres had been inflated correctly when they were put on the car and that tyre pressures will vary depending on the rubber's temperature, thus sitting on the grid and cooling will mean the pressures drop.

"You check the tyre pressures in the tyre heaters when you put them on the car," said Wolff. In other words, Mercedes were oblivious to the situation as they prepared their cars on the grid.

Toto Wolff has just told reporters that there will not be a penalty issued against Mercedes and Lewis Hamilton.

So why did Mercedes ask Hamilton to speed up late in the race?

Upon learning they were under investigation, Mercedes asked Hamilton to push to create a gap in case of a time penalty. With a performance advantage in hand, it made sense to get as far clear of the pack as possible with a retrospective drive-through penalty, for example, meaning a 30-second post-race time penalty.

"We didn't understand what was going on," Wolff said. "There could have been possible penalties. And in order to gain a little bit of a margin, we asked him to push."

Would Hamilton's tyre pressures have affected his performance?

Teams tend to run tyre pressures as low as they can get away with for a performance benefit. But in this case Hamilton insisted there was no gain. "That's what Formula 1 is all about," he said. "And for whatever reason today – if it's 0.3 it's 0.3 – but it had no effect on the car. That small amount on the tyre doesn't do anything." Wolff reckoned it might, if anything, have had a detrimental effect. "At the end of the day, it can cost performance if you have one tyre that has a different pressure than the others," he added.

Lewis Hamilton says that tyre pressure gave him no advantage in the Italian Grand Prix, and argues that he won the race because he was simply fastest.

Why do tyre pressures matter anyway?

As with plenty of other technical matters in F1, the word 'safety' is at the forefront of this particular subject. "You don't have any choice in the matter," Force India's Bob Fernley said. "Whether you're happy or not is irrelevant – it's a safety issue. So you have to abide by it." Even on a standard road car, tyres with insufficient pressure in can eventually overheat and cause tread separation. 

But Anthony Davidson argued afterwards that the current protocol, to a degree, misses the point.  "I don't care what a cold pressure is," he said, "because in a safety sense the important thing, and what they target, is the running pressure."

And what might the impact be in the longer-term?

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