Rosberg mystified by lack of pace

Rosberg, competing in his maiden race at the IMS, failed to make the first cut in qualifying after struggling to find speed in his car.

The Williams driver, using a new engine this weekend, was only 19th fastest.

"Going out in the first session is not what we wanted but it was very difficult and I couldn't feel the car properly," said the German. "The grip wasn't there and if I can't feel the car, I can't push for those extra few tenths without making a mistake.

"We don't really know where the problem is, but we knew today would be difficult for us."

Teammate Mark Webber also endured a tough day, struggling to find grip. The Australian will start from 12th place.

"We need a lot more grip than we could muster today, a bit like the situation in Montreal, but the pace of the Ferraris is very strong, indicating the tyres are okay, so we just need to work harder with the car," said Webber.

"We have struggled on the infield section all weekend, balancing wing level, top speed and grip. Sunday sometimes shows a different pace relative to the competition, so we'll see tomorrow, but it might be quite tough for us."