Lewis Hamilton has called on Pirelli to keep faith with the current Formula 1 tyres after being left dismayed by the 2021 rubber.
All 20 drivers were handed two sets of next year's medium tyres that were used at varying stages across the two practice sessions ahead of this weekend's Bahrain Grand Prix.
Newly crowned seven-time F1 champion Hamilton was initially stumped when asked for his verdict so as to avoid being too disparaging.
Eventually, Hamilton said: "Oh God! I'm trying my hardest to say anything.
"What I want to say is that weekend in weekend out every year we've got a team here from Pirelli. I have the utmost respect for the guys that load our tyres up, bring them here and keep us safe. They do an amazing job.
"Unfortunately, we've had the same tyre for the last two years. At the end of 2019, they brought a new tyre - which each year they normally do - and it was quite a bit worse.
"So they said 'Okay, we'll keep the tyre we had from last year '. They've had two years now to develop a better tyre and we've arrived with a tyre that's three kilos [per set] heavier. It's like a second worse per lap.
"I know for the fans that doesn't really make a difference but from a driver's point of view, we're working with brands and partners who are at the forefront of technology and elevating moves forwards.
"If you're going back after two years of development, I don't know what's happening. It definitely doesn't feel good out there, and it's a worry.
"I'd prefer to stay on these tyres if that's all they've got and that's the best they can do, which it clearly is, then it would be better just to stay with this tyre."
With downforce due to be reduced on next year's cars, Pirelli may be forced to follow Hamilton's suggestion and retain this season's rubber for 2021.
Hamilton finished the day quickest at the end of both sessions as he showed no let-up just two weeks after claiming his latest drivers' title.
In daylight running in FP1 Hamilton finished almost half-a-second quicker than Mercedes team-mate Valtteri Bottas, while under the lights in the evening air of FP2, the Briton was a third-of-a-second clear of Red Bull's Max Verstappen.
The Dutch driver's time, however, was set on the current medium compound while Hamilton was on the soft. The drivers were left largely frustrated with how quickly they overheated.
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