Jarno Trulli says he found the 2009-specification Toyota 'nearly impossible' to drive in the wet conditions at Portimao yesterday, but is confident that the TF109 itself has good potential.
The first major 2009 test has been blighted by poor weather all week, and Trulli admitted that the reduction in aerodynamic grip under the new rules made life very difficult.
"There is a massive drop in downforce and grip," he said. "In the conditions it was very difficult to get temperature in the tyres. It was really hard for everyone out there and it was nearly impossible to drive. This is the first feeling!"
But despite his concerns over the new generation cars' wet weather handling, Trulli is optimistic about Toyota's prospects for the season.
"The car doesn't seem to have any big problems and it has run really well in the past few days with Kamui (Kobayashi) so I will say we are pretty confident about this year," he said.
"We just need to get into the normal testing with warm conditions and probably this could be the case in (the next test in) Bahrain."
Trulli is also hopeful that the 2009 rule changes will improve Formula One's spectacle, although his Toyota teammate Timo Glock is concerned that the braking distances will still be too short to allow much passing.
Although Trulli found it hard to judge the new package yesterday, he believes the changes have the potential to increase overtaking.
"I can say we expect so, yes," he said. "We will have some overtaking manoeuvres and some spectacular races.
"But practically I can't say because it's difficult at the moment to judge. This is the goal and this is the target, to have a better race for all of us."
The veteran Italian hopes the days of a driver's race being ruined by a poor start will be over.
"Before if we had a difficult start or a difficult first part of the race we couldn't recover because it was impossible for us to overtake," said Trulli. "We just want to have a better chance to enjoy it more on the track and for everyone to enjoy the race with more action."
But Glock is more sceptical, feeling that the revised wings might not make enough of a difference.
"There is a big rule change in F1 this year with the aerodynamics and everyone hopes that it will be possible to overtake more," he said.
"My feeling is it will not be a big change in terms of overtaking because it is still possible to brake quite deep into the corners with these cars and especially with these tyres."