Ferrari chief Jean Todt has defended the decision to report their Formula One rivals for using what they believe are illegal tyres and said they were just doing what any team would have done in the circumstances.

"What do you think would have happened if the Bridgestone tyres on a Ferrari were too wide?" the Ferrari sporting director said in an interview with Sunday's edition of German paper Frankfurter Allgemeine Sonntagszeitung.

"Do you think they would have kept quiet? They would have crucified us. They would have accused us of cheating.

"Our opponents would have demanded we be disqualified for all the races it could be proven we had used illegal tyres."

Ferrari, the constructors' champions for the past four years, believe the Michelin tyres used by most of their rivals are illegal in race conditions and admitted last week they had told the governing International Automobile Federation (FIA).

Michelin insist their tyres conform to the rules but, within days, the FIA announced tighter checks on front tyres at the next race at Monza.

The issue came to light after Michelin-shod teams filled the top seven slots at last month's Hungarian Grand Prix and Ferrari's world champion Michael Schumacher limped home eighth on his Bridgestones after being lapped.

Todt said the fact that they did not report their suspicions at the Hungary race proved the issue was not a matter of sour grapes.

"It's our view that such an issue shouldn't be discussed at the race," he said. "We didn't want to harm the sport. But I'll tell you -- that was not an easy decision. Our opponents should explain why they think we're sore losers.

"We didn't challenge the race results in Hungary even though we could have. There was enough evidence there."

Gerhard Berger, motorsport director for BMW who power the Williams team, said he understood why Ferrari was protesting.

"Ferrari's challenge is legitimate," he told Der Spiegel news magazine. "If we knew that our competitors had something that was perhaps outside the limits we would also want to have that controlled."