Johnson switches to back-up car

Johnson's car was damaged in a wreck during Wednesday's second practice session, ahead of Thursday's Gatorade Duel qualifying races for the season-opening Daytona 500.

The Hendrick Motorsports driver damaged the front end of his car after running into the back of Denny Hamlin, when he took avoiding action of an accident triggered by Mike Bliss getting loose and being hit by Joey Logano.

Logano and Bliss will also need their back up cars after both hit the wall and each other. Along with Johnson, they will start from the rear of the field in their respective Duels, where their starting position for Sunday's race will be determined.

"When I hit the back of [Denny Hamlin], it kind of shifted the nose over and rolled it up," Johnson said. "We can beat it back into place where we think it's going to be right, but there's just no guarantees we can fix it right 100 per cent.

"With the risk of tomorrow's race, the fact that we might need a back-up car, this one is going to be stripped down and taken back to Charlotte and fixed on the plates so it's right. It's more to make sure that we're really ready with a strong bullet for the 500."

During the first practice of the day Clint Bowyer cut a tyre and got collected by Derrike Cope and David Reutimann, the three of them sustaining major damage to their cars and being forced into their back-ups.

Brian Vickers also spun during the day's first practice, while Dale Earnhardt Jr and Jamie McMurray almost caused a major pile up when they made slight contact at the sharp end of the drafting group later in the same session.

Many drivers have chosen to do very limited running to avoid damaging their primary car for Sunday, as in five practice sessions that have taken place so far, there have been frequent incidents involving several drivers.

"I thought things were wild," Johnson added. "And here's the biggest problem. Guys have different theories on where they want to blend on the race track. Some people stay on the bottom; others think they blend on the top. Either way there is a draft of 18 to 20 cars coming and we're like a snake weaving through these cars, and cars coming in and off at different speeds.

"I don't believe that's what caused this wreck, but there were a lot of other crazy moments because of that. I need to go to the tape and see what happened here because I was just riding along and thought everything was fine, and the next thing you know, I was in the middle of it."

Matt Kenseth and Marcos Ambrose set the fastest times in the two sessions, followed by Kyle Busch who was second fastest in both.