Italian GP: F1 stewards investigate Hamilton and Rosberg over tyres

FIA technical delegate Jo Bauer's report said the top four cars on the Monza grid - the Mercedes and Ferraris - had their left-hand tyres checked on the grid after the five-minute signal.

While the Ferraris were within Pirelli's 19.5psi tyre pressure specification and 110-degree tyre blanket temperature, both Mercedes were outside the marks.

Hamilton's tyre was measured at 0.3psi below, Rosberg's at 1.1psi under.

Championship leader Hamilton went on to win the race, having been urged by his Mercedes team to push as hard as possible and extend a lead over Sebastian Vettel's Ferrari in the closing laps. He eventually won by 25 seconds.

Rosberg had been running third behind Vettel until a late engine failure ended his race.

Pirelli had raised its tyre pressure specifications for the Italian GP, though it said the decision was unrelated to the tyre failures and related controversy in Belgium a fortnight earlier.

Mercedes technical chief Paddy Lowe said the team was confused by the summons.

"We don't understand it to be honest," he told Sky Sports.

"We've been summoned to the stewards, so we'll go there and explain it.

"All I know is we set our pressures fully supervised by the Pirelli engineer.

"He was perfectly happy with them as they were set."

Lowe confirmed that the instruction to Hamilton to push was related to the potential for a penalty.

"With an abundance of caution, we thought let's make a gap," he said.

Hamilton said he "wasn't aware" of the stewards' investigation and declined to comment.