Williams driver Juan Pablo Montoya said he chose not to move to McLaren until 2005 because his current team has a better chance of success this year.
Montoya thinks Williams' new car has an excellent chance in 2004
The Colombian revealed in November that he is to switch teams next year.
Speaking at the launch of Williams' new FW26 car on Monday, Montoya said he felt McLaren's plan to change factories in 2004 would affect their chances.
"I think Williams have a better chance of winning the championship this year than McLaren," said Montoya.
"McLaren are changing factories this year and I think 2005 will be a good year for McLaren.
"Williams have been totally focused on the car for this year. Things might not work out that way but that's the risk you take."
Montoya insisted his forthcoming move would not affect his performances for Williams, who have unveiled a radical new design for the 2004 season.
"While I am a Williams driver I will give it 100%. We're here to win, simple and that's the aim," he said.
"The team will be committed to me.
"Anybody who knows Williams knows that their main priority is winning the constructors' championship."
Montoya was third in 2003 and was in the running for the title - until sixth place at the penultimate Grand Prix in the USA left him too far behind champion Michael Schumacher.
The Colombian's claims that Williams have a great chance in the 2004 championship was backed by co-driver Ralf Schumacher.
"I think this year will be my best chance of winning the title but I think it will go down to the wire, as it did last year," he said.
And the German, who finished fifth in last year's title race, warned Williams' rivals that their experiences in 2003 would serve the team well this year.
"We expect to be very competitive this year. Last year we never thought about it (the championship) and then all of a sudden we were going for it.
"I think now we all know what it takes, we learned from last year.
"It's fair to say that, yes, it might be the season where we have the best-ever possibility of winning it."