TALLADEGA, Ala. _ Dale Earnhardt Jr. had a tire explode during practice Friday, starting a multicar accident and destroying the back end of the No. 88 Chevrolet.
Earnhardt will go to a backup car for the Amp Energy 500 Sunday at Talladega Superspeedway and start in the back of the field. But the team changed an engine because of a cylinder head problem earlier in the day, so he would have started in the back anyway.
Earnhardt was leading a pack of cars racing near the top of the track in Turn 3 when his right rear tire exploded, completely blowing the sheet metal off the back of the car.
"I think we ran over something," Earnhardt said. "It came out of nowhere. It's unfortunate because a lot of man hours go into building these cars."
Earnhardt's primary car was the Chevy he drove to win the Bud Shootout All-Star race at Daytona in February. His backup is the car he raced to a ninth-place finish in the Daytona 500 one week later.
Earnhardt isn't the only driver going to a backup car because of Friday's crash. David Gilliland was racing behind Earnhardt and had nowhere to go. He ran into Earnhardt's car as it turned into the wall.
"It was wild," Gilliland said. "It was a big explosion. The right rear quarter panel came off [Earnhardt's car]. It's frustrating because there's nothing you can do."
Stewart hit Gilliland and Kahne ran into Stewart, causing Stewart to spin down into the infield grass.
"I just saw tire flying and then smoke," Kahne said. "I didn't know where to go. It tore up the front of our car enough that we'll definitely go to a backup car. It's too bad."
Stewart's team believes the No. 20 Toyota is repairable, so he won't go to a backup car.
Reutimann was further back in the pack and damaged his No. 44 Toyota when he was hit from behind. He will switch to the backup car.
Earnhardt and Kahne returned to the final practice in their backup cars.
Qualifying, which usually takes place on Friday, is Saturday for this race. The Amp Energy 500 is an impound race, meaning the teams can't make changes to the car after qualifying.
Terry Blount covers motorsports for ESPN.com. He can be reached at email@example.com.