by Reid Spencer
Tony Stewart was fifth fastest in Saturday's first Sprint Cup practice session, but trouble found him when his right rear tyre exploded and took most of the right rear quarter panel and side window with it.
Stewart, who had completed the most laps (20) to that point in the session, qualified eighth for Sunday's Dickies 500 but now must start from the rear in a back-up car.
The substitute chassis (#203) made its debut in February at California, where Stewart finished seventh. The backup chassis also finished second at Atlanta in March and seventh at Texas in April in its last two appearances this season.
Misfortune in the early practice wasn't confined to Stewart either.
Approximately eight minutes into the session, Robby Gordon slammed the wall between Turns 1 and 2. Robby will also start Sunday's race from the rear of the field in a back-up car.
Jeff Gordon, who will start on pole, meanwhile struggled through Saturday's final practice and was only 33rd fastest on the speed chart.