Vettel happy after 'good start'
World champion Sebastian Vettel laid down a marker for the 2011 season by setting the fastest time on the opening day of testing in Valencia.
The 23-year-old German marked his first outing in Red Bull's new RB7 car with a lap of one minute 13.769 seconds.
His closest rival in a 2011 car was Ferrari's Fernando Alonso, 0.784 secs off the pace and fifth overall.
Nico Hulkenberg and Paul di Resta of Force India and McLaren's Gary Paffett all made the top four in 2010 cars.
It is difficult to read too much into the lap times, especially on the very first day of testing for the new season.
This is a time for experimentation - with some teams launching their new cars and other still using last season's models - and fuel loads are unknown.
Regulation changes for 2011 mean teams can now deploy an adjustable rear wing but devices such as 'F-ducts' and double diffusers have been banned.
Kinetic energy recovery systems (Kers) return after a one-year absence and Pirelli have replaced Bridgestone as the sport's sole tyre supplier.
"It is difficult to say [how our main rivals are faring], we haven't seen all the cars, particularly the McLaren car," Vettel told BBC Sport after the first of three days' testing.
"This was the first day and it's very hard to draw conclusions with so little running - we need to have more running on track to see where we are.
"It is practice for all of us, different programmes, different days and we need to be aware of the big teams - hopefully us and I guess McLaren, Ferrari and Mercedes.
"Also maybe a surprise like Renault, who perhaps have an interesting concept.
"It is different to last year, so many things changed, so we will see how we get on. The car does feel a bit different but not that much."
Mark Webber will share the Red Bull duties with Vettel on Wednesday before having the car to himself on Thursday.
It is day one and not much time between Abu Dhabi and here - 10 weeks - but for the guys to build a car that has no issues is, I reckon, good news. We can be happy and proud of what we have achieved so far
Vettel completed 93 laps of the track and his flying lap was 0.17 seconds quicker than that of second-place Hulkenberg (71 laps).
McLaren reserve driver Paffett (91 laps) set a time of 1:14.292 to finish third, with fellow Briton Di Resta 0.692 seconds off the pace in fourth.
Two-time world champion Alonso, who will also drive on Wednesday before Felipe Massa takes over for Thursday, racked up an unrivalled 97 laps in the new Ferrari F150.
The Spaniard chalked up a fastest lap of 1:14.553 before coming to a halt at the final corner when his car ran dry - perhaps as part of Ferrari's test strategy.
"I think generally it is better to be on top of the rankings rather than being on the other end," added Vettel, the youngest-ever F1 world champion.
"It was the first day and it was most important to do laps, which we did - 93 laps is quite an achievement and looking back it is something we never got as good at on the first day over the last two or three years, so that is a very good sign.
"On top of it I feel quite comfortable in the car, I enjoyed myself today and I think it was a good start."
"Today was day one for most of us, and it is a long, long way - long testing season, before we start racing again in Bahrain [on 13 March] and then a very, very long season - 20 races.
The general impression is that it felt very good - the whole car is a big step forward for us. There is more to come, certainly on the aerodynamics front, over the next few weeks
"So even if you start with the best car, things can change so you need to keep the development up.
"Right now, we have just done the first step and we can be happy and proud of what we have achieved so far.
"It is day one and not much time between Abu Dhabi and here - 10 weeks - but for the guys to build a car that has no issues is, I reckon, good news."
Former world champion Alonso was also happy with his day's work.
"I'm satisfied with how this first day has gone, in particular regarding reliability. We haven't had any kind of problem - just as we haven't had any in the factory before arriving here," he said.
But he said it was absurd to read too much into the first run-out of the new year.
"It's impossible to have an idea of how the different teams line up after just a few hundred kilometres and I don't think that we will have a clear picture before the Bahrain Grand Prix," he said.
"I remember that last year at the last test in Barcelona we were sixth fastest with Sauber and Force India ahead of us. At Sakhir we lapped them. I think that this question mark will remain right up to the first race."
However, there was frustration for Mercedes after a hydraulics problem caused Nico Rosberg to stop on the track with only nine laps in the bag.
That issue restricted Schumacher to just 16 laps in the afternoon session and the seven-time world champion was 2.681 seconds off the pace.
It meant a disappointing end to a day that started with the British-based team launching their new MGP W02, but Rosberg was upbeat.
"The general impression is that it felt very good," said the 25-year-old, who finished 70 points above team-mate Schumacher last season.
"The whole car is a big step forward for us, which all stems from the way the company is working, which is a lot better.
"There is more to come, certainly on the aerodynamics front, over the next few weeks."
Valencia testing results, Tuesday:
1 S Vettel Red Bull-Renault* 1 minute 13.769 seconds (93 laps)
2 N Hulkenberg Force India-Mercedes 1:13.938s (71)
3 G Paffett McLaren-Mercedes 1:14.292 (91)
4 P di Resta Force India-Mercedes 1:14.461 (28)
5 F Alonso Ferrari* 1:14.553 (97)
6 K Kobayashi Sauber-Ferrari* 1:15.621 (68)
7 J d'Ambrosio Virgin-Cosworth 1:16.003 (71)
8 V Petrov Renault* 1:16.351 (28)
9 M Schumacher Mercedes* 1:16.450 (15)
10 J Alguersuari Toro Rosso-Ferrari* 1:17.214s (19)
11 R Barrichello Williams-Cosworth* 1:17.335s (77)
12 N Karthikeyan HRT-Cosworth 1:18.020s (45)
13 N Rosberg Mercedes* 1:19.930s (9)
*= 2011 car