Ferrari driver Sebastian Vettel believes Mercedes' most powerful qualifying engine mode is still his rival's strongest weapon in this year's title fight.
After finishing a distant third in 2016, Ferrari has made a remarkable return to form this year and at the midway point of the season Vettel leads Mercedes driver Lewis Hamilton by one point in the standings. However, his advantage has been eroded by 24 points in the last two months as Mercedes has found form at a series of high-speed circuits and scored three victories and four pole positions from four races.
"It is probably true that at the last couple of races Mercedes have been stronger," Vettel said.