Hakkinen concerned about brake wear

The German street track is made up of only four corners, but it has two heavy braking areas, and Hakkinen is expecting some drivers to have problems if they do not take care of their brakes.

"The brakes are a very big issue here," he said. "You have to look after them, and it is important to be consistent.

"If you go flat out from start to finish, you will probably get some problems, so you really have to be cautious with the way you use the brakes."

The former Formula One world champion admitted that Mercedes seem to be in good shape for this weekend, but he added that they cannot afford to be too confident.

All of the 2007-specification Mercedes cars were in the top seven in practice on Friday, while the highest 2007-spec Audi driver was Martin Tomczyk in 14th place.

"It looks like we are very competitive, very strong," Hakkinen said. "But it doesn't mean we can relax.

"We still have a long list of things that could be better, and the challenge is now for the engineers to make those improvements that could find us two or three tenths of a second."