Ralf Schumacher has warned his brother Michael, joint championship leader, that sibling ties will not stand in the way of him trying to strengthen his championship charge in the Spanish Grand Prix on Sunday.

The younger Schumacher took his first grand prix victory at Imola a fortnight ago, confirming what many had suspected : Williams are back with a bang.

And now as the Formula One circus brings its tents to the Circuit de Catalunya for the Spanish Grand Prix, the younger Schumacher warned that the kind of on-track spat that led to the brothers refusing to speak to each other after last year's race could happen again.

"I don't have a brother on the track," the Williams driver said. "If one of us was to say he was delighted the other one was faster, he would be lying. I don't feel I'm in his shadow," he added. "He is Michael, I am Ralf. And there isn't anything about him as a racing driver I am jealous of."

That was proved when the two banged wheels as they tussled for position in the closing stages of last year's race. In that instance, Ralf lost the battle and frosty relations between the pair were only thawed by the intervention of their father Rolf.

Spain represents perhaps the best chance yet for Ralf and Williams to blow the title race wide open. The young German has been quick here in the past, scoring a useful fourth place for the team last year and armed this year with what is now acknowledged to be the fastest car on the grid, Schumacher could pose an even greater threat.

That threat could be further strengthened by Williams' tyre supplier, Michelin. The French company come to Barcelona with more knowledge of the circuit than any other, having spent most of last year developing their tyres at the track.

However, all Michelin's work could be undone by the reintroduction of traction control at this weekend's grand prix. Until recently all of Michelin's testing had been carried out on cars running without the controversial technology, which returns for the first time since 1993. The return of mechanical traction control means tyres will behave in subtly different ways, particularly in the area of degradation as the cars will now not slip and slide through corners.

Bridgestone will be in the same boat, however, and the hope for Williams is TCS will prove as revelatory to the Japanese manufacturer as it has to the French.

But those hopes will ultimately depend on the great variable: the weather. Despite the brilliant sunshine and 20 degree temperatures that greeted the teams on arrival in Barcelona yesterday, rain has been forecast throughout the weekend. With Michelin suffering badly against Bridgestone's wet and intermediate tyres, Ralf Schumacher's fighting words may prove empty if he can't steer the Williams car through a crowded field in the middle of downpour.

Much will also be expected this weekend of David Coulthard. The McLaren number two's remarkable run of reliability has brought him four podium finishes so far and thrust him into joint leadership of the championship. The Scot produced an amazing drive here last year, despite suffering broken ribs in a near-fatal air crash the week before, to claim his second consecutive second place.

All he has to do on Sunday, then, is get by Michael Schumacher and in Barcelona that will be no easy task. Although the Circuit de Catalunya is regarded as a McLaren stronghold, the Silver Arrows' dominance here is a recent thing. In 10 visits to the circuit, the world champion has never finished outside the points. He won in 1995 for Benetton and '96 for Ferrari, and finished on the podium a further five times.