Williams expects to start 2015 F1 season 'scrapping' with Ferrari

Despite finishing behind Red Bull in third in the constructors' standings, Williams was world champion Mercedes' closest rival on pace in 2014.

It was Mercedes' nearest challenger again in the final test at Barcelona last week, ahead of Ferrari.

However, Williams's chief test and support engineer Rod Nelson believes a mistake by Sebastian Vettel hid Ferrari's true potential.

The German's super-soft tyre run on the final day of testing was four tenths of a second slower than Williams driver Valtteri Bottas's effort on the same rubber, but Nelson thinks that was deceptive.

"I think he pushed too hard at the start of the lap and lunched the tyres by the time he got halfway round," said Nelson, when asked by AUTOSPORT where Williams is in the pecking order.

"So I expect Ferrari to be a little it closer than maybe it looked.

"We're going to have a scrap with them, certainly at the start of the season."

He admitted that Mercedes looks out of reach, having beaten Williams and Ferrari's super-soft times on soft tyres.

"Mercedes are looking incredibly strong. I'm sure its pace made a lot of people sit back a little bit.

"It certainly made us think twice, but we should be in the hunt for podiums."

MORE RISKS IN 2015

Williams had its most successful season in more than a decade last year, scoring six podium finishes as it recovered from finishing ninth in the 2013 standings.

Nelson said the team's strong 2014 meant it could feel more comfortable taking risks this year.

"After the 2013 season, we were obviously focusing on regular points so we were probably relatively risk-averse," he said.

"We had to get a good stash of points before we moved forward from that and then we were targeting podiums. Then if things had gone our way we could've got a win or two.

"This season I think perhaps we'll be less risk-averse.

"We have a level of performance, it remains to be seen what it is but I think we've got a reasonable idea.

"We can be reasonably confident that we should be challenging for good points at most races."