Chasers involved in practice wreck

Earnhardt was running at the front of the pack while completing the second practice session of the day when the right-rear tyre on his car blew, sending him into a spin and igniting a wreck that involved at least five other cars.

The Hendrick driver has been forced to go to his back-up car as a consequence, giving up on his primary machine, which he had raced to victory at the non-points season opening Budweiser Shootout.

The crash put an end to a difficult day for Earnhardt and his team, as they had already been forced to change an engine after hitting trouble during the first practice of the day.

"The tire seemed to come apart at the tread and the sidewall," said Earnhardt Jr. "We looked at the car and really nothing had fell off of it. It came out of nowhere. It was hard to see.

"We looked at some of the replays to see if anything came out from under it - maybe we can find it on a replay there was something we might have run over."

Also caught in the incident was Tony Stewart, who ruled out a tyre failing on Earnhardt's car being to blame for the crash. His crew managed to repair the car following practice and he won't be forced to switch to his back-up machine.

"I guess the 88 [Earnhardt Jr] had a tyre let go in front of us and there wasn't anything he could do and there wasn't anything that anyone else could do," Stewart said.

"We were all so close, and that is one of the risks of practice is something like that happening. He only had 13 laps on that tyre so I don't think it was a Goodyear issue by any means.

"I think he just ran over something - there's no reason a tyre would have failed like that."

Clint Bowyer was the third title contender involved in the wreck and as with Earnhardt Jr, he has switched to his back-up car for the reminder of the weekend. Kasey Kahne, David Reutimann and David Gilliland were also involved in the crash, all of them switching to their back-up machines as well.

Brian Vickers topped the drafting session, while Jeff Burton had been fastest in the morning practice.