Kyle Busch switches to backup car

LAS VEGAS -- Jimmie Johnson and Kyle Busch crashed in separate practice incidents Saturday at Las Vegas Motor Speedway, forcing both drivers to go to backup cars and start Sunday's Sprint Cup race at the back of the field.

Busch will have to give up his front row starting spot after damaging his primary car in the first practice session Saturday. Johnson, who would have started sixth, wrecked in the final practice Saturday afternoon.

Busch brushed the wall exiting Turn 4 and damaged the right rear quarter panel and the frame. The No. 18 Toyota team decided it was better to switch to the backup car.

Busch, who grew up in Las Vegas, qualified No. 2 Friday with a lap at 190.040 mph and would have started outside the front row next to pole winner Kasey Kahne.

Johnson slammed into the Turn 2 wall at the start of the final practice, doing major damage to the back end and the right side of the No. 48 Chevrolet.

Johnson is a four-time winner at Las Vegas, including the 2010 event. Busch won at LVMS in 2009.