NASCAR rule about back-up cars

Here’s a question for Dopers who really know their NASCAR:

This week, qualifying for the Pocono 500 was rained out. So the field was set by points, which put point-leader Tony Stewart on the pole.

Then Stewart wrecked his car during practice. Because he switched to a back-up car, he had to start at the rear of the field.

Which got me to thinking… The way I always interpreted the start-in-the-back rule was: If you race using a different car (or engine) than the one you qualified with, you go to the back. Clearly, since there was no qualifying this week, my understanding of the rule is incomplete. There must be some other action besides qualifying which officially establishes a team’s # 1 car for the race.

So, what is it? Backing the car out of the hauler? Driving onto the track for any reason, whether it’s qualifying or practice? Or maybe teams must notify NASCAR in advance which car they intend to use?

I don’t know for absolute sure, but I know that the cars did go through NASCAR inspection on qualifying day. I imagine that would lock them into the car.

I agree with what dzeiger said.

I’ll admit that initially, I did not think anything weird with Tony having to go to the back, but after reading the OP from Wheelz, I wondered also: “Yeah, why did he have to start at the back if he never did qualify the car”

But I suppose, once a car has gone thru inspection, they are locked to it makes kind of sense.

NASCAR apparently doesn’t actually publish its rulebook or make it available online. I would guess that each team has to register a chassis and engine number with NASCAR at the start of each weekend, and replacing either means you are in a “backup” car.

I have a copy of the 1996 Craftsman Truck Series rule book. It has the same procedure for qualitying and backup cars as the current Sprint Cup rules. It states that if a team must go to a back up car once** their primary car is submitted for inspection**, that team will start at the back of the field. Inspection takes place prior to qualifying. The go to the back rule also applies if a team changes engines, transmissions or rear ends, makes any unapproved changes to the car, changes the driver of record or fails to participate in all practice sessions. There are a few new rules that apply to races that use the impound rule that was not in effect in 1996.

Looks like I have my answer! Thanks, racer72!