McLaren and Williams should be able to mount an even stronger challenge to Ferrari in 2004, according to their tyre supplier, Michelin.
Wet-weather testing is an important part of Michelin's winter programme
Michelin motorsport boss Pierre Dupasquier said he has been encouraged by progress made in winter testing.
"Our teams have commented favourably on the progress we have made, particularly with regard to rear tyres. It has been a good start," the Frenchman said.
Dupasquier said improving wet-weather performance was a major focus.
Michelin's improvement in performance from 2002 to 2003 was a major factor in the tight championship battle staged throughout last season.
But the efforts of McLaren and Williams were hampered by the continuing poor performance of Michelin's wet-weather tyres in comparison to Ferrari's Bridgestones.
These caused major problems when it rained at the penultimate race US Grand Prix, effectively ending the hopes of Kimi Raikkonen and Juan Pablo Montoya.
Michael Schumacher won the race to all but tie up the title he finally clinched at the final round at Japan's Suzuka track.
Rain at the US Grand Prix helped Schumacher's bid
Dupasquier said: "Our teams have been taking part in a wet-weather test programme.
"There has been a fair amount of rain at Barcelona, Valencia and Jerez. This worked in our favour because we wanted to evaluate our latest wets and didn't have to soak any of the circuits artificially."