The long-running Firestone-Ford tyre saga took a new twist yesterday when a federal appeals court in Chicago reversed an earlier ruling that had granted class-action status to millions of product liability claims.

The court said a single trial would be unmanageable. The ruling means each of the estimated three million owners of 1991-2001 Ford Explorers and 15 million Firestone tyre owners who want to sue the giant car and tyre companies will now have to bring their own individual product liability actions in their own states.

"We are pleased the U.S. Court of Appeals for the Seventh Circuit has reversed the class certification," Ford said in a statement.

"The Court recognised that Ford and Firestone have already addressed the tyre issue by replacing nearly 30 million tyres and that the National Highway Traffic Safety Administration (NHTSA) has investigated the safety of the tyres and Explorers and did not find any additional action to be warranted."

The ruling relates solely to the Ford Explorer SUV and Firestone Wilderness tyres. It does not affect hundreds of personal injury lawsuits filed against the companies that are awaiting court hearings across the US.

Ford and Firestone lawyers argued that varying state laws and personal circumstances of the litigants would have made a single class-action case unmanageable.

The previous court ruling in Indianapolis - overturned yesterday - had allowed Explorer and Firestone tyre owners to form class actions. "This decision confirms what we have been saying all along: the issues and circumstances involved in these no-injury lawsuits are far too varied to certify class certification. It would make the legal process less efficient and less manageable, exactly the opposite of what a class action is intended to achieve," Firestone said in a statement."