Renault say their new car is a more "aggressive" design than last year's
The Renault, Sauber and Lotus teams have unveiled their new cars for this season, with all three setting a target of being more competitive.
Renault aim to move up from fifth place in 2010 to challenge the top four, Red Bull, McLaren, Ferrari and Mercedes.
Sauber aim to score regular points and improve on eighth place overall.
And Team Lotus, the best of three new teams who spent last season at the back, aim to battle with the midfield and eventually challenge Renault.
Team Lotus and Renault are
embroiled in a row over the use of the Lotus name in F1
after the Group Lotus car company pulled out of its relationship with Team Lotus and decided to sponsor Renault.
A High Court trial to settle the dispute is scheduled to start on 21 March, a week after the first race of the season in Bahrain on 13 March.
The car looks good, but what is most important is that it goes quick
Renault, like Sauber, took the wraps off their new car at the Circuit Ricardo Tormo in Valencia, where the first pre-season test starts on Tuesday. Team Lotus,
who launched their car via an official e-magazine
, are joining that test on Wednesday.
Renault ended the season as the most competitive of these three teams, and their lead driver Robert Kubica mixed it with the big teams on several occasions in 2010.
The Pole, one of the most highly rated drivers in F1, said he was optimistic the team could take a step forward in 2011.
"(It has been a) long break, after a good last year so I'm really looking forward to test the new car, a new baby for the team and we hope it will be a good one," Kubica said.
"The car looks good, but what is most important is that it goes quick, so let's hope we have a competitive car."
Technical director James Allison said: "Words like 'aggressive' and 'innovative' are very much in vogue in Formula 1 at the moment, but where the R31 is concerned we feel those adjectives are appropriate.
"It's true to say that the car has been designed in an ambitious manner and a quick glance at the layout will confirm that its entire concept differs considerably, not just from last year's car, but from any car this team has ever produced."
The Renault has very low rear bodywork, which is reminiscent of last year's McLaren, and appears significantly different from last year's bulky-looking R30.
Kubica's team-mate will again be the Russian Vitaly Petrov, and the team have signed Brazilian Bruno Senna as their third driver.
Swiss Romain Grosjean also has that title but BBC Sport understands Senna - who made his debut for back-of-the-grid Hispania in 2010 - is the official reserve.
Senna said: "If any of the other drivers happen to be poisoned or break a leg or something like that, then they may not know who's to blame but they know who is going to replace him."
The new Renault has been painted black-and-gold, a deliberate attempt to reflect one of Lotus's historic F1 liveries from the 1970s and 1980s.
Team Lotus aim to make a major step forward in 2011
Team Lotus, spurred on by their intense rivalry with Renault and a bitterness over the behaviour of Group Lotus, have set catching Renault by the end of the year as one of their targets.
Competing as Lotus Racing in 2010, the team were the best of three newcomers but they failed to score a point.
Driver Jarno Trulli said: "Last year we aimed to finish the race. This year we aim to finish in the points and with this package it should be achievable."
Sauber said their target was to finish higher than last year's eighth overall.
The name of the new Lotus, the T128, is a continuation of the history of Lotus F1 cars and follows last year's T127.
"This year's car is a much more contemporary design," technical director Mike Gascoyne said of the new design, in classic Lotus green and yellow livery.
"The car really will be a midfield runner. It's a modern F1 car I'm very confident it is a big step up and it's the start of a process that takes Team Lotus back to the front of the grid."
Sauber are targeting regular points finishes from the new C30
Italian Trulli will again be joined by Finnish driver Heikki Kovalainen in a car that looks substantially different from the 2010 model.
"There's been almost no carry-over of parts for the 2011 car, whereas normally you'd have a substantial carry-over and the chance to optimise last year's parts," explained Gascoyne.
"It has a much more current feel about it. And it's the basis of our cars for the future."
Gascoyne, a former designer for McLaren, Tyrrell, Jordan, Renault and Toyota, has said that
he believes Lotus can be competing with Renault by the end of the season
Sauber owner Peter Sauber said his aim was to mix it with the teams fighting behind the big four teams.
"We want to finish in the points regularly and clearly improve our position in the world championship.
"2010 marked the 41st year of our company history and one of the most difficult. But we managed to overcome these difficulties in the second half of the season.
"We implemented some well-considered structural changes. The appointment of James Key as technical director already bore fruit last season, and he is now in charge of development of the Sauber-Ferrari C30.
"At the same time, we have managed to secure our business foundation for the 2011 season. In these economically straitened times that is something we can be proud of too."
Sauber said the new car had been designed to eradicate the weaknesses of its predecessor - aerodynamic efficiency, low-speed cornering, mechanical grip and to gain more flexibility in suspension tuning.
Sauber are continuing with Japanese rising star Kamui Kobayashi, who impressed with some stirring drives and dramatic overtaking moves in 2010.
And they have taken on the Mexican rookie Sergio Perez, who finished second in the GP2 feeder series in last year and comes with backing from telecommunications company Telmex.
The Swiss team's car will do some promotional running at Valencia on Monday ahead of the start of the first pre-season F1 test at the track on Tuesday.
World champions Red Bull and Mercedes will both launch their 2011 challengers on Tuesday.