By Andrew Benson Motorsport editor

Schmacher insists he is confident in Bridgestone's tyres

Ferrari will struggle to retain their Formula One world titles this season because of inferior tyres, Renault star Jarno Trulli says.

Ferrari's Bridgestone tyres have looked less competitive in winter testing than the Michelins used by other top teams.

Trulli, who said the new Renault was showing promise, told BBC Sport: "It's difficult to judge how much quicker the Michelins are, but they are quicker.

"I think Ferrari will have a tough time this year - the same as last year."

Ferrari are scheduled to unveil their 2004 car at their Maranello factory in Italy on Monday.

And world champion Michael Schumacher has played down fears about his tyres after he drove last week for the first time since the end of last season.

The German said: "Bridgestone is very motivated and well prepared.

The car seemed pretty competitive straight away Jarno Trulli Renault driver

"Like I have said before, during the season it will go up and down, just like Michelin will. We'll see at the end of the season who's in front. It will be very close."

Ferrari are introducing their new car much later than major rivals McLaren and Williams.

McLaren tested their car for the first time in December, while Williams have been running since the beginning of this month.

Both teams, like Renault, use Michelin tyres.

Ferrari have started the last two seasons with their previous year's car after not being convinced of the reliability of their new model.

But Schumacher said he believed he would be starting the season in Melbourne on 7 March with the definitive 2004 car.

"At the moment, our intention is to use the new car in the first race. We're not thinking of any other scenarios," he said.

Renault were also a major threat in 2003, winning one race with Fernando Alonso, and Trulli said he was confident they could have another strong season after testing the R25 in Spain last week.

The Italian said: "I did the shakedown, the first two days, which is always a bit tricky because when you do the first two days you have plenty problems with the car.

"But apart from that everything has been running well, especially in the next two days.

"Everything has been sorted. Fernando did a lot of laps and the car seemed pretty competitive straight away."