McLaren may be looking good on the timesheets but Jenson Button says they are finding it "a little bit tougher" over long runs.
The Brit finished Friday's practice for the German Grand Prix seventh on the timesheets with a 1:19.221. His time put him 0.880s off the pace.
But while Button was happy with his qualifying style pace, he fears McLaren are lacking over a longer distance.
He revealed: "Looking at the timesheets, you'd say we look quite good, but we're finding it a little bit tougher over the long runs.
"I think we're overheating the tyres under traction. It's so difficult to manage the tyres in these temperatures, and it's especially hard to get the Supersoft tyre working correctly without overheating it."
Friday's running at the Hockenheimring saw McLaren and their rival teams all run without the FRIC suspension system.
"The car didn't feel any different without our FRIC system - it wouldn't really make a massive difference around here anyway," Button said.
He added: "As ever, we'll just make the best out of what we've got - and I think we can push a bit harder tomorrow."