Valencia: Lewis Hamilton and Jenson Button have called for a big push from their McLaren team after finishing fourth and sixth at European Grand Prix.
Both McLaren drivers were unable to match the pace of rival teams Red Bull or Ferrari throughout the 57-lap race at the Valencia street circuit.
Fourth-placed Hamilton, 26, stressed that he had not had an upgrade to his car for several weeks despite having struggled with high speed grip for some time.
"I think we`re quite a bit down on downforce," he said, "We`ve not made an upgrade for several weeks now.”
"We`ve had upgrades like the front wing for example but rear downforce, we`ve really been struggling with that."
The 2008 champion said he was also worried that McLaren could be even further off the pace at Silverstone in two weeks time, when new rules restricting exhaust set-ups will come into play.
"I think in the next race we`ll really, really struggle," Hamilton warned.
"Once we lose the engine map (blown exhaust) I think we may see some differences there."
Fellow Briton Button, 31, also said it was important that his team improved the car ahead of his home race.
"We need some good upgrades," he said.
"We need to get our heads down and improve the car, the package. Aerodynamically I think we need an improvement for Silverstone because we`re not moving forward and that`s what we need to be concentrating on.”
"I do know of some new parts that are coming but I think we need more. We need to take some risks because behind us is a big gap - this race anyway - to the Mercedes and the Ferraris are in front of us and the Red Bulls are miles away."