Mercedes wary of Ferrari's renewed threat in Belgium

While Mercedes heads into the second half of the F1 season with a 147-point lead over Ferrari in the constructors' championship, the situation in the drivers' standings is much tighter.

Sebastian Vettel's victory in the last race prior to the summer break in Hungary, combined with a bad day for Mercedes duo Lewis Hamilton and Nico Rosberg, means the Ferrari driver trails Hamilton by 42 points.

Wolff knows not to discount a four-time champion in Vettel with the might of Ferrari behind him.

"Clearly Ferrari have made a big step forward, winning two races fair and square, although you can say they weren't our best days either," said Wolff, speaking to Autosport. "We've won eight of 10 races, so looking at the pure statistics we should be in good shape.

"But we take Ferrari very seriously, and this is the mentality we have going into the second half of the season. It would be narrow minded and naive of me not to expect Ferrari to be competitive.

"Our ambition is clear in that we want to win the drivers' and constructors' championships again.

"So we need to keep both feet on the ground, work on our strengths, eliminate our weaknesses as much as possible, and get the job done."

One of Mercedes' core strengths this season has been the reliability of the cars, with both Hamilton and Rosberg in the points in all 10 races to date.

"Our sporting and mechanical reliability has really been encouraging this year," said Wolff. "We really made a big improvement from 2013 into 2014, and now we've made an even bigger jump from last year into this year.

"If you push performance in the way we do, and with new technologies, and you make the car last then that is encouraging.

"But we're only mid-season, so let's be careful, let's not take the reliability we had in the first half of the season for granted. This is still a mechanical sport and things can change very quickly, with Hungary the best example."