Rivals warned Mercedes F1 power unit will be stronger in 2015

This weekend's first running of 2015 cars, in the first pre-season test at Jerez, should offer some insight into how much each engine manufacturer has improved over the winter.

Mercedes was well clear of its rivals throughout last season, and the early indications from Mercedes' partner teams is of the German car manufacturer having made good gains over the winter too.

Force India technical director Andrew Green has no doubts that the Mercedes 2015 power unit will be improved over the one that won 16 out of 19 races last year - with more to come later in the campaign.

"From the data we have it's definitely got better from last year," Green told AUTOSPORT.

"And I'm expecting another step in the middle of the season too. We're excited about that."

Lotus CEO Matthew Carter said that his team had been impressed with the way its new relationship with Mercedes was working, and was predicting good things from his new power unit.

He also reckons that with Ferrari and Renault eager to make the most of opportunities afforded by in-season development, that Mercedes could start the campaign very strongly having made a bigger push to find improvements for the first race.

"Having Mercedes is a huge opportunity for us," said Carter.

"We don't know what Honda is going to be like, but Ferrari and Renault are obviously looking at doing changes later in the year - which means there will not be that much early on.

"That could give us a bit of a big advantage earlier in the season."