It was about the width of a single leaf of paper, but it was too much. The Car of Tomorrow chassis built by Richard Childress Racing flunked an in-house inspection because a door bar was 17 thousandths of an inch too low.

It was the third time the Childress team had junked a car because it didn't comply exactly with the razor-thin tolerances allowed by NASCAR's Car of Tomorrow inspection process. And it was when Bobby Hutchens began to wonder exactly what it was going to take to get one of them onto the racetrack.

"For about a week of two," said RCR's vice president for competition, "panic probably set in on all these Cup teams."

Now, the time for panic is past. The Car of Tomorrow, a project seven years in the making that promises a safer, more competitive racing environment, becomes a reality with Sunday's Food City 500 at Bristol Motor Speedway. All the questions about how long it will take the COT to be inspected, how well it will race, and whether it will hold up to the rigors of the Nextel Cup Series will begin to be answered Thursday morning, when haulers carrying the new vehicles enter the half-mile track in East Tennessee.

What's received the most attention thus far is the appearance of the car, which features a splitter under the nose and a rear wing that will be issued by NASCAR to teams as they arrive at the racetrack each week. It's also taller, with added headroom for a driver who is moved more toward the center of the vehicle. The goal is to provide a more aerodynamically-balanced racecar, with adjustable parts that lower costs by negating the need for track-specific vehicles.

That's the idea, at least. Yet despite months of work by race teams and tests on every conceivable type of track, no one will really know how the COT will perform under race conditions until the green flag drops at Bristol on Sunday.

"There's just too many unknowns right now," said five-time Bristol winner Jeff Gordon. "Once we get through the race and we understand that car a little bit more, then we can probably answer some of those questions. But it's going to be an interesting weekend from the time trucks and crews get to the track to the time we leave, because it's about going through inspection."

Inspection is the teams' most pressing concern. During the COT test at Bristol earlier this month, it took more than an hour for just one car to pass through the multi-stationed inspection process. Instead of the standard individual templates, a large shell drops down over the top of the vehicle. The process is tighter than ever; all the cars that went through inspection on the initial day of the Bristol test failed on their first attempt.

That experience led NASCAR to open the garage at Bristol a day earlier than usual, to give cars more time to get through technical inspection without missing practice laps. Inspection begins at 10 a.m. Thursday, with the first practice session set for 10:30 a.m. Friday.

"The big question is still the inspection process. We left the Bristol test with as many questions about the inspection process as we went there with. To be quite honest, I suspect NASCAR did, too," Jeff Burton said.

"As many things as they're trying to inspect, it's going to be a learning process, and we're nervous about that. We'll certainly go in there wanting to abide by the rules and not be caught up in the middle of something, but it's conceivable that a team could get caught up in the middle of something without trying to be in the middle of something. NASCAR and teams together are going to have to find a way to work through those things."

Then there's the whole issue of how the car will perform on the racetrack. NASCAR is purposely beginning the COT phase-in on tracks like Bristol and Martinsville where aerodynamics are less of a factor, saving intermediate and restrictor-plate venues for the latter stages of the rollout process. Denny Hamlin turned the fastest lap of the Bristol COT test at 122.170 mph, well off the track record of 128.709 set by Ryan Newman in 2003.

But most of the testing was done in single-car runs, and not in the tight packs Bristol is known for. And setups varied wildly from one day to the next as teams struggled to come to grips with an unknown.

"It's going to take a while for the teams to adapt and realize what kind of setup it's going to take to make the drivers comfortable. I think we saw that for sure at Bristol [during the test]," said Kevin Bayless, chassis and aero manager for GM Racing.

"The setups that the teams were running at the end of the second day ... were considerably different than what they unloaded with and what they run with the current cars. So I think it's too early to say how the competition will pan out until the teams have had more time to work with the cars. It certainly appears the tools are available for the racing to be at least as good as what it is currently."

Not that everyone is entirely comfortable with what they've learned about the COT thus far. "As far as preparation, speed and all that, we are fine," Gordon said. "The frustrating things for me are that, compared to the racecar we have been driving, this car is nothing like it, and it won't do any of the things you would want it to do."

Already teams have discovered quirks, like the inclination of the COT's left-front tire to bounce in the corners at Bristol, an issue crew chiefs tried to remedy through setup changes over the course of the test. And there will surely be other idiosyncrasies, some that won't fully manifest themselves until Sunday.

"Overall, I don't really know what to expect," Kyle Busch said. "We're just going to be all over the place. A couple of guys were talking about 'bouncing room' because we go into a corner and bounce up the racetrack because the springs are so stiff. We're going to have to leave each other about three feet of room when we're trying to pass each other. It's a tough race."

The uncertainty and unfamiliarity have many fans and competitors alike wringing their hands over the impact the COT will have on NASCAR. Burton, for one, believes that on Monday morning, everyone will wonder what all the fuss was about.

"For 12 months there's been this big aura of terrible things coming with the Car of Tomorrow, and when we get there it's going to be a race and somebody is going to do better than other people," he said. "I honestly believe that when you look back at the Bristol race, with the exception of seeing a wing on the top and a splitter on the front, it's still going to look like a Bristol race. I really believe that."