BARCELONA, Spain -- Carrying different goals for the 2016 Formula One season, Mercedes and McLaren unveiled their new cars on Sunday.

Mercedes hopes to improve on only a few weaknesses of last year's Silver Arrows, while McLaren brings what it calls a "significant number of innovations" to try to get back to the front of the grid after dismal results in 2015.

Mercedes was clearly ahead of other teams in the last two seasons, easily winning the drivers' and constructors' titles. McLaren is coming off a nightmare year under a renewed partnership with engine supplier Honda, finishing second-to-last in the constructors' championship.

The new cars were introduced on the teams' websites a day before the first session of preseason testing begins in Barcelona.

Mercedes unveiled the W07 chassis featuring "quite a lot of mini revolutions" compared to its predecessor.

"After a highly successful season all round in 2015, our priority has been to identify the areas in which we were weakest and to try to improve on those," Mercedes technical director Paddy Lowe said. "While we had some fantastic results last year, there are many areas in which we can still be much better."

Mercedes won two consecutive titles with Lewis Hamilton, and teammate Nico Rosberg was runner-up both times. The duo won all but three races last season.

"It's another carryover year from a regulatory point of view and potential gains inevitably become harder to find," Lowe said. "While the car may look very similar to its predecessor from the outside, underneath there are quite a lot of mini revolutions that make up an overall evolution for the new season."

Mercedes hasn't been seriously challenged since major rule changes were introduced in 2014. Again it's expected to be a step ahead of other teams when tests begin on Monday.

McLaren unveiled what it called a "striking and innovative" MP4-31 chassis that integrates "elegant aerodynamic solutions" with the new Honda power unit developed exclusively for the team.

"The aero package shows fantastic attention to detail. The whole car is beautiful in fact," two-time world champion Fernando Alonso said. "It's particularly nicely packaged from an aerodynamic point of view. I'm 100 per cent ready for the challenge ahead."

An eight-time constructors' champion, McLaren was only better than Marussia last year. Alonso and Jenson Button scored 27 points between them.

"Despite the ups and downs we saw last year, there were steady improvements all year long, and that gives us confidence in the design direction we're taking," Button said. "There are a lot of positives we can build on, and a strong platform to take forward."

Nobody was ready to make any bold predictions, though, as the team is unlikely to start contending for podiums and victories in 2016.

"We'll make no predictions as to when those wins will come," McLaren chief Ron Dennis said. "But I can say without fear of contradiction that every member of our team has worked with truly relentless dedication over the past few months."

Honda struggled developing the complex V6 hybrid-power turbo engines that were introduced in 2014. The team dealt with performance and reliability issues all season long.

"We won't know exactly where we stand until we reach the end of the two tests," said Yasuhisa Arai, Honda's senior managing officer. "But we're looking forward to getting back on track, gathering data, and feeding back the information to our engineers so as to prepare for Melbourne and onwards."

The first race of the season is the Australian Grand Prix on March 20.