F1 tyre-swap ban a major factor in Mercedes' German GP woes - Brawn

Just a week after the Brackley-based team appeared to have made a breakthrough in tyre management with victory in the British Grand Prix, Lewis Hamilton and Nico Rosberg endured a tough afternoon at the Nurburgring.

Pole position man Hamilton complained all race about a lack of grip as he was powerless to stop main rivals Red Bull, Lotus and Ferrari finishing ahead of him - while Rosberg never recovered from the team's qualifying error that left him 11th on the grid.

Brawn reckoned that a combination of not being able to swap rear tyres, plus high track temperatures on Sunday, exposed the ongoing weakness of the W04.

When asked to explain why the team struggled so much, Brawn said: "The construction of the tyre has changed and I think the ability to swap tyres before was a good way of offsetting the stress of the tyre.

"You could use it in qualifying and then swap it, and have it in a different condition for the race.

"You cannot do it with these tyres, and I think we were back into going over the limit of the temperature of the tyres and suffering from it.

"The first half of the race was pretty horrible. In the second half, the fuel weight went down, it got a touch cooler and we got back in the window again.

"The times were respectable, so it shows how critical we are.

"On high fuel at the beginning of race when we were trying to push we overstressed the tyre, and we need to find solutions to overcome that."

Although Mercedes' strong form in Monaco, Canada and Britain pointed to big strides having been made in tyre management, Brawn revealed that he still had doubts ahead of the German GP.

"I never thought we were on top of the issues," he said.

"There were some things like swapping tyres on the rear that was helpful and that has disappeared.

"Silverstone wasn't that warm, and Montreal was not warm.

"I said we would need a hot race, and this [the German GP] was like some of the races earlier in the year where we struggled until things cooled down a bit."