The Mercedes Formula 1 team has been impressed with the pace shown

The reigning F1 world champion squad spent most of pre-season away from the top of the timesheets, but raised eyebrows in the paddock with some impressive long runs and occasional fast laps that were often quicker than rival cars, but set using harder compounds of tyre.

Although Mercedes looks clear favourite heading to the season-opening Australian Grand Prix, team boss Toto Wolff said reliability concerns, plus the pace shown by Ferrari and Williams, gave cause for caution.

"I wouldn't really try to read too much into laptimes, because we don't know what fuel loads people were running," Wolff told AUTOSPORT.

"We would be trying to read a crystal ball and that's not what we should do and not what I would like to do.

"Although we have been running solid and the pace is good and the long runs are good, reliability is still an issue.

"It's always going to be an issue for everybody and we need to get on top of that and then just wait and see how the first couple of races pan out. Then it's probably easier to confirm what we've seen in testing.

"Ferrari has been looking good, Williams has been looking good, so let's wait until the racing really starts."