Sebastian Vettel says “it’s difficult to understand” the pace jumps by Mercedes at each round this season.

Mercedes recently lost its lead in the Formula 1 world constructors’ championship to Ferrari when it suffered a double mechanical DNF in the Austria Grand Prix after looking to have had a pace edge on its rivals – boosted by an aerodynamics package update which debuted at the Red Bull Ring.

Despite taking three wins in 2018, Vettel feels Mercedes’ pace has been the most inconsistent out of the front-runners so far this season having seen the German manufacturer struggle in Monaco, where the team has suffered in recent years, as well as Canada which had been a Mercedes stronghold before his victory in Montreal last month.

“With Mercedes it’s sometimes difficult to understand why they are up, why they are down,” Vettel said “With Red Bull, they are more consistent. There are certain types of tracks that maybe suit them, and others that don’t.

“You don’t know what’s going on. We’ve had our races where we’ve been very strong, and others where we weren’t very strong for some reasons, and then we were able to improve in those areas.

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“Apart from lap one, if you take France as a weekend then it was very positive, especially if you compare it to Barcelona – similar asphalt, same tyres – and so on. We were in a much better place. Why Mercedes are so competitive, and other times not, I don’t know.”

Following Mercedes’ disaster in Austria, Vettel has reclaimed the F1 world drivers’ championship lead from Lewis Hamilton by a single point while Ferrari has also taken the world constructors’ championship lead by 10 points.