Audi decide to remain in ALMS

However, the champion team remain outspoken in their belief that the rules are now too heavily weighted in favour of their LMP2 rivals.

The Le Mans organisers have restricted the LMP2 cars this season to ensure a performance disparity between the LMP1 and LMP2.

But the ALMS opted not to apply this restriction as Audi and Intersport are the series' only LMP1 representatives, whereas LMP2 is growing in stature after the arrival of works-backed Porsche and Acura entries. The rulemakers therefore felt that it was in the ALMS' best interests to allow the LMP2s to be competitive with the LMP1s.

This - and other restrictions applied to the R10 TDi after its dominant performances in 2006 - left Audi frustrated, and led to uncertainty about their continued participation in the series.

They have now decided to continue with the championship, but only after discussions with the ALMS authorities, and the team remains unhappy about the regulations.

"The diesel racing commitment in the American Le Mans Series is important for promoting diesel engines in America," said Audi sport boss Dr. Wolfgang Ullrich.

"That's why we decided to continue competing in the American Le Mans Series.

"We know, however, that in view of the current technical regulations, it will be very difficult for us being successful in the upcoming races.

"Audi is accepting this challenge nevertheless. We've had some positive discussions with the management of this racing series concerning the future developments of the rules."

An Audi statement said that the current regulations left the R10 with "serious handicaps".

"The roughly 150 kilogram lighter Acura/Honda and Porsche LM P2 sports cars which, due to a change of rules, are allowed to compete in the American Le Mans Series with more engine power than at Le Mans, were already nearly equal to the Audi R10 TDI in the Sebring season opener on account of the regulations," said the statement.

"On the slower street courses, such as St. Petersburg, their benefit from the 150 kilogram weight advantage in the LMP2 class will even be greater, as it affects acceleration, cornering speeds, braking distances and fuel consumption considerably.

"Still worse for Audi, the Audi R10 TDI - as a diesel sports car - has to compete with a fuel tank that has been reduced by ten percent: instead of 90 litres, the fuel tank contains no more than 81 litres in 2007.

"At Sebring, this restriction already resulted in the Audi drivers having to refuel up to five laps earlier than the LMP2 cars - despite the low consumption figures of the diesel engine. In St. Petersburg, the situation will be similar."

This weekend's race is the first of three consecutive rounds on street circuits, with St. Petersburg followed by Houston and Long Beach.