Rosberg: It was riding on full attack on low fuel

Nico Rosberg gave a hint of Mercedes' true speed on Tuesday, with the fastest time on the first day of Formula One's final pre-season test, and then said there was still room for improvement.

It was the first time in 2016 testing that the world champions had led the timesheets at the end of the day and Rosberg was not even using the quickest tyres to go faster than everyone else.

The German lapped the Circuit de Barcelona-Catalunya with a best time of 1:23.022 after using Soft Pirelli tyres for the first time this year.

Next best on similar tyres was McLaren driver Fernando Alonso, albeit 1.7 seconds off Rosberg's top lap time.

The German was also two tenths of a second faster than Valtteri Bottas who was using the Ultrasoft Pirelli tyres on his Mercedes-powered Williams.

"Today in particular we tried qualifying, to see where the one-lap limit is," Rosberg told media. "It was riding on full attack on low fuel - and that felt super... even if I have to say that there is still room for improvement."

"It’s all the more enjoyable taking the car to the limit and really pushing. It’s been a good test, reliability has been good, the speed has been there – it’s all working to plan," added the Mercedes driver.