The owner of the Chrysler auto company, Cerberus Capital Management, has unwittingly put its finger on the biggest challenge that Detroit's embattled carmakers face in proving their long-term viability.

Reacting to the Bush administration's $17.4bn lifeline to General Motors and Chrysler last Friday, the buy-out group noted that until last June, Chrysler had "met or exceeded every financial metric in our underwriting plan, with the exception of top-line revenues".