Sebastian Vettel: Mercedes' F1 reliability better than my laptime

The four-time F1 world champion set the pace on the first day of pre-season testing at Jerez on Sunday, but lost a large chunk of running to a telemetry problem with the SF15-T.

Although Vettel ended up nearly half a second quicker than Nico Rosberg's Mercedes, he suggested the fact Rosberg clocked up nearly 100 more laps than Ferrari was a greater achievement.

"I think laptimes are not that important in the end - it's the amount of laps [that counts]," Vettel said.

"Surely it's better to be closer to the front rather than a long way behind, but I think in terms of laps there's still a lot of improvement we can do.

"The reference is still Mercedes, they did 150-200 laps today, so they've proven they start off with a very reliable car - hopefully not as quick as last year.

"I think that's what everyone is hoping for, but you have to give fair credit to them - they're doing a very good job.

"It will be a surprise if they're not as strong as they were last year."

Despite the telemetry problem that limited his running, Vettel said he was pleased with progress in his first official test with the Scuderia.

"It would have been nice to do more laps but overall I think we can be quite happy," he added.

"The first impression was quite good.

"Obviously it's difficult to say at this stage, but for day one I think we can be reasonably happy."