In a recent interview, Rubens Barrichello described this year's Williams-Cosworth FW33 as "aggressive". It's a sentiment shared by technical director Sam Michael as it made its track debut this morning.

"Until you start testing," says Michael, "you're never sure how you're going to stack up against the opposition, but we're optimistic. We think this is a good car, but we'll have a better overall picture in a few weeks time."

New rules, which were only confirmed by the FIA's World Motorsport Council in June 2010, compelled Williams F1's technical team to take an innovative approach to its new car. The ban on double diffusers and the F-duct forced the aerodynamicists to seek new downforce solutions; KERS had to be incorporated into the layout and the team had to prepare for the arrival of a new tyre supplier, Pirelli, for the first time in five years.

"The design of this year's car has been pretty smooth," the Australian continues. "We've improved our way of working by increasing the communication between the mechanical and aerodynamic departments, and that improved our decision making processes. It allowed us to increase the optimisation time spent on each part of the car."

The car seen at today's Valencia test is the first iteration of the FW33. This 'launch spec' will be replaced by an aero upgrade at the first race in Bahrain and there will be many others during the course of the year.

Sam Michael and his technical team expect aerodynamic performance to reach the same levels as 2010, despite there being less aero freedom in the rules.

Aerodynamic work started in December 2009, with the mechanical aspects of the FW33 beginning in March 2010. The major layout decisions were finalised in June, following the World Motorsport Council's confirmation of the 2011 rule changes, and the new gearbox was on the dyno by September. The launch spec aerodynamic package was completed in November, since when the aero team has focused on the first-race upgrade.

The seven-speed 'box is the smallest ever produced by Williams F1 and works in conjunction with the new pull-rod rear suspension. "With gearbox usage increasing from four to five races this year," says Michael, "reliability is vital. But I'm not expecting it to be a problem because the new gearbox has the same stiffness characteristics as the old one and the rulebook forces us to be conservative with the internals. For the last few seasons the ratios have to be 12mm wide and 600g per pair, whereas in the past we were down to 8-9mm gears."

"The double diffuser ban is pretty significant," he continues. "Not only can you not open any holes between the reference and step planes, you must have continuous material through all lateral and longitudinal sections. The scope for developing anything on the diffuser is limited, so we're looking at the centre, rear and front of the floor, as well as the sides of the floor and the little area around the tyre spat, all of which are still free.

"The ban on double diffusers should tighten up the field. It will probably happen straight away, but even if it doesn't and someone comes to the first or second test with something you hadn't thought of elsewhere on the car, it'll be easy to replicate it and get it onto the car quickly because it shouldn't affect the underlying car structure such as the gearbox."