Robert Kubica has claimed that modern Formula 1 cars need to trim some fat.

The Pole is uniquely positioned to comment on today's cars, having sat out the period between 2011 and 2017 with his arm injuries.

"The first thing I noticed was the weight," the new Williams tester told Auto Motor und Sport.

"The cars are now at least 60 kilograms too heavy. In slow corners, it feels like a bus."

Although today's cars are quick on the stopwatch, Kubica recalls with relish what it was like to drive the cars of last decade.

"They weighed 605 kilograms and had 50 kilos of ballast on board," said the former BMW and Renault driver.

"The tyres also had a shorter life so you could attack the whole race. It's impossible today. You have to manage everything."

Kubica said that drivers are also managing the engine, and working closely with engineers to operate the cars and follow the plan.

"From the outside it looks like the drivers are all on their own, and that's because everyone is keeping their distance because of overheating," he explained.

When asked what the answer might be, Kubica answered: "Bring down the weight. Then many problems will resolve themselves."

As for the engineers helping the drivers on the radio, Kubica thinks that has little to do with the complex technology.

"The drivers today may have gotten lazy," he said. "I see no reason why a good driver needs any instructions from the pits."

The 2018 F1 season begins later this month in Melbourne.