LONDON (Reuters) - Dominant Formula One world champions Mercedes have 'chinks in their armour' that Williams must be ready to exploit this season, according to the latter team's technical head Pat Symonds.
Speaking to Reuters, Symonds declared himself "reasonably optimistic' about the latest wind tunnel data and looked forward to seeing how that translated on track when testing starts in Spain next month.
"I’m not an optimistic person but I know the improvements we’ve made to the car are greater than we made last year," he said.
"I have to say I am quite pleased with the improvements on paper that we’ve made with the car."
Williams, once dominant as their current engine partners Mercedes are now with Britain's triple champion Lewis Hamilton and Germany's Nico Rosberg, have finished third in the constructors' championship for the past two seasons after a period in the doldrums.
Last year, Frank Williams' staunchly British team finished ahead of Red Bull, themselves dominant champions between 2010 and 2013, and the season before that Williams pushed Ferrari into fourth place.
The team that have won more constructors' crowns (nine) than any team apart from Ferrari (16) in the history of the sport, and are third on the all-time list of race winners, have not tasted the victory champagne since 2012, however.
There are those who doubt whether any 'customer' team can nowadays win in normal conditions against a well-funded 'works' outfit owned by the manufacturer and using the same engine, but it has been done before.
Ferrari-powered Toro Rosso won at Monza with Sebastian Vettel in 2008 while Brawn won both 2009 championships with Mercedes engines at a time when McLaren were the German manufacturer's favoured partners.
"I still want to believe that we can (beat Mercedes)," said Symonds.
"If they are running their engines a bit harder than us, which of course they are perfectly entitled to do, and that’s worth a 10th of a second then we’ve got to make a car that is a 10th of a second quicker than theirs to get on equal terms. Well, why not?
"Red Bull, Ferrari have got much greater resources than us, so have McLaren. And all of those are teams that we have beaten in the last couple of years. We can do it."
Brazilian driver Felipe Massa, a winner with Ferrari before joining Williams, agreed that in a year of evolutionary change, with stable regulations rather than anything revolutionary, it could be possible.
"We are really near. We were on the podium a few times last year and maybe more times the year before in 2014," he told Sky Sports at the weekend. "We really hope we can get back to the victories... I really hope it can be possible."
Red Bull's Australian driver Daniel Ricciardo won three races in 2014 when Mercedes dropped the ball and a resurgent Ferrari, with four-times world champion Vettel joining from Red Bull, did the same last year.
"Even if you get as dominant a situation as Mercedes have got, we are not in the McLaren 1988 era when they absolutely win every race," said Symonds, referring to that team's Ayrton Senna/Alain Prost era.
"Mercedes have chinks in their armour. There aren’t many because they are an amazingly strong team but we’ve got to be there for those days.
"At the same time we have to keep pushing ourselves so we are not (just) looking for that way of doing it, ultimately what we want to do is beat them fair and square. That’s what we’ve got to aspire to."
Symonds recognised that Williams must also cut out the mistakes, of which they made far too many last season, to have any chance of doing that.
The memory of Finland's Valtteri Bottas lapping on mismatched tyres -- colour coded to make it even more glaringly obvious -- after a muddled pitstop at the Belgian Grand Prix in August remains a painful one that cannot be repeated.
"We certainly made far too many operational errors last year, there’s no doubt about it," said Symonds.
"In my pre-season briefing to the guys at the beginning of the year we concentrated a lot on that.
"I can’t say we will be faultless, nobody is immune... but certainly the number of errors we made was way too high and we are working hard to try and improve that."
The season starts in Australia on March 20.
Reporting by Alan Baldwin, editing by Pritha Sarkar