Britain's Lewis Hamilton says he is unhappy with the revised tyres that Pirelli brought to the German Grand Prix after he faded from pole to fifth.
Pirelli strengthened the rear tyres for the race at the Nurburgring after six drivers suffered blowouts at Silverstone last Sunday.
Hamilton, 28, said: "I have nothing positive to say about these tyres.
"We didn't have any blowouts this weekend, but I don't particularly like the tyres."
He added: "I don't understand why we struggled so much on them, but that's motor racing. The only positive is that we got some points.
"It's a shame because the team is working so hard and doing such a good job. Clearly we've got a good car, but for some reason it just doesn't work on these tyres.
"But everyone else is getting on with them, so we have to work harder."
Mercedes arrived at the Nurburgring on the back of victory in the British Grand Prix - their second win in three races courtesy of Nico Rosberg.
Hamilton put himself in the best position to secure his first victory for Mercedes by taking pole position.
But the Briton went backwards in the race as the car struggled in the hot conditions - something that has been an ongoing problem for the team this season - as track temperatures hit 45C.
He dropped to third when Red Bull's Sebastian Vettel, who went on to win the race, and team-mate Mark Webber passed the Mercedes at Turn One, before fading to fifth place.
Team-mate Rosberg, who finished ninth, added: "We struggled a lot with the rear tyres and that's why we weren't able to match the pace of the guys in the front.
"We need to understand the new tyres a bit more because it seems that the new construction has shuffled things around, especially in these hot conditions."
Team principal Ross Brawn said that while the team have made progress with their performance in hot conditions, they are still trailing their rivals.
"We have said all along that there is still a question mark over our performance in hotter conditions, and today's race showed that we still have work to do," he said.
"We have made big steps forward since Bahrain and Barcelona, where we particularly suffered with hotter track temperatures, and our performance was much improved compared to those races.
"But we have not yet done enough to convert our Saturday pace into race-winning speed in all conditions on Sunday.
"The three-week break until Hungary will give us an opportunity to think about how we can make further progress on our tyre management as well as continuing to develop the core performance of the car."