Bernie Ecclestone has backed Pirelli, amid criticism of the Italian supplier's 2019 tyres.

Recently, Haas boss Gunther Steiner slammed the tyre situation this year as being "not Formula 1".

"We should not be constantly talking about whether a tyre works," he said.

The big complaint is that the so-called tyre operating 'window' is too narrow, while the new Pirellis are hard to keep up to temperature.

That is despite the fact that Haas was competitive in the winter tests in Barcelona, while the first four races of the year have been difficult for the American team.

Steiner said: "If it's the same in Barcelona, I do not understand the world anymore."

"I think in the past Mercedes sometimes had problems with the tyres overheating. The new tyres are doing the opposite," said Sebastian Vettel.

"Our car was not bad in Baku, but it was difficult to find the operating window of the tyres," the Ferrari driver added.

Andy Green, the technical boss at Racing Point, admits that tyres are a big preoccupation for the teams this season.

"Unfortunately it changes from track to track, asphalt to asphalt. We are having to learn it every time," he told Auto Motor und Sport.

Haas' Steiner continued: "Pirelli changed the design of the tyres. The tread is thinner and so it's harder to keep the heat in them."

Mercedes has won all four races this year, but former F1 supremo Bernie Ecclestone pointed out that at all of those races, the hierarchy seemed up for grabs.

"Imagine if everyone understood the tyres. Then the order would always be the same," he said.