Mexican GP: Mercedes cooling 'on the edge' after Rosberg brake fire

The constructors' championship-winning team was fastest in practice two at Mexico City, but both Red Bulls and Sebastian Vettel's lead Ferrari were all within half a second of Rosberg's best time, while Lewis Hamilton was in that pack and only fourth quickest.

Both Mercedes drivers said cooling will be a big issue this weekend, due to the thin air at high altitude in Mexico.

"We're really on the edge here with the brakes, because if you cool them more you lose performance," said Rosberg.

"You open up the car [for cooling], so you lose downforce and you go slower.

"So you always want to try to be on the edge, and here specifically it's quite difficult because we are so high up.

"The air is very thin, so it doesn't flow very well through the car."

Hamilton added: "Cooling is going to be a problem for everyone this weekend.

"We're going to have to manage it, but everyone is in the same position."

Red Bull's Daniil Kvyat and Daniel Ricciardo were two and three tenths of a second off the pace respectively, and the Australian said that was a better performance than the team was expecting.

"Today definitely looked better than we thought it would be," said Ricciardo.

"All these tight, twisty corners and the esses in the middle, I think they work to our advantage.

"What we lose on the straights, we gain in the corners.

"Because the track was so low grip today, it helps having a bit more downforce on the car.

"That's where we were able to make the difference and stay with the front group.

"If we can stay here where we are, within a few tenths of Mercedes, we would be very happy with that."

Regarding car cooling, he added: "You're running more or less at the limit here.

"You're trying to put on all the bits that keep the car cool. The whole car is being tested here."