-- When NASCAR's championship battles aren't competitive down the stretch, the last few races of the season can lull fans to sleep with their tedium. The points leader tends to race conservatively so he won't blow his shot at the title, while other drivers tend to lose their fire once the championship is beyond their grasp.

But when multiple drivers are in the hunt for the crown, as is the case this season -- with $5 million at stake, three races to go and the top three drivers separated by just 75 points -- fans can stand back and watch the sparks fly as tactics of all sorts are trotted out, from mind games to dirty driving to plain old not playing fair.

The last is the latest charge to fly around the NASCAR garage, leveled Saturday by third-place challenger Greg Biffle at Tony Stewart and Jimmie Johnson, who are first and second in the standings, as drivers prepared for Sunday's Dickies 500 at Texas Motor Speedway.

According to Biffle, Stewart's and Johnson's race teams skirted NASCAR's limits on testing last month to gain an unfair competitive edge in next week's race at Phoenix International Raceway.

Biffle was among the drivers who tested at Phoenix last month, having saved his last test for the one-mile oval. NASCAR permits teams only seven tests each year to control costs and keep the playing field level. That's why it surprised Biffle to see Johnson, who had run out of tests, at Phoenix, too. But instead of testing his own No. 48 Chevy, Johnson tested a No. 25 Chevy that, according to Biffle, was one of Johnson's own cars cloaked in the paint job of his teammate, Brian Vickers, who drives the No. 25.

As for Stewart, he didn't show up at the Phoenix test. But his No. 20 transporter truck was there, and out rolled a Chevy painted the same color as Stewart's car but with a No. 80 on the side, indicating it belonged to Stewart's teammate Denny Hamlin. Hamlin did the driving over the two-day test, but Biffle said he was convinced the purpose was to collect data for Stewart in one of Stewart's racecars.

"It's not fair," NASCAR spokesman Jim Hunter conceded. "We've known there was a loophole there, but to police it with all the testing that has been done, we'd have to have people all over the country at every track on any given day."

NASCAR is overhauling its rules on testing for 2006, Hunter said, partly to close that loophole that allows drivers who have run out of tests to sneak in extra track time by testing under a teammate's number. But until the new rules kick in, Stewart and Johnson haven't violated anything. In fact, Hunter conceded, their crew chiefs might just as well be applauded for leaving no stone unturned in their quests to win the championship by exploiting a gray area.

"To be perfectly honest, absolutely," Hunter said, asked whether teams would be better served by bending the rules. "That's one thing about our sport: No matter what the rules are, if there's any gray anywhere, somebody is going to find a way to use it to their advantage."

The finer points of NASCAR's testing rules are stock-car racing minutiae, on one hand. But on the other hand, minutiae is the foundation of NASCAR's rulebook, which is a mind-numbing compilation of specs, weights and measures dictating the size, shape and composition of every conceivable part on a racecar, from cylinder heads to lug nuts. NASCAR's restrictions on testing are no less important.

A two-day test session yields invaluable data about how to attack a particular racetrack, especially given that NASCAR teams get only two 45-minute practice sessions to figure that out on race weekend.

Biffle explains: "That's all the practice we get for the entire weekend! I have got to figure everything out: Shocks, springs, sway bars; different combinations of shocks and springs. What if I want to do some tire-pressure information? Is a higher tire pressure better? Lower? These shocks with these springs? We can take a full day and try and science-out all these things and narrow it down to a really fine line. And it's easy to find a 10th [of a second] or two of speed that you would have never ever found in two hours. Not even possible of finding in two hours."

Johnson didn't exactly come clean with his team's ruse, however, insisting he was just trying to help out Vickers's team -- which would be benevolent indeed, considering that Johnson is battling for a championship and Vickers didn't even qualify for NASCAR's postseason.

"I was filling in for the 25" team, Johnson said. "I'm not the only one that's been in somebody else's equipment or with somebody else's number on the side. There's been a lot of people doing it. It's just kind of how it is."

As for Stewart's team, crew chief Greg Zipadelli said that the "No. 80" the team tested at Phoenix was, in fact, one of Stewart's cars -- his third backup that he doesn't intend to race at Phoenix anyway.

"What difference does it make what cars they take?" Zipadelli said. "It's Joe Gibbs Racing that took cars out there."

Greg Biffle, left, says Tony Stewart's and Jimmie Johnson's teams skirted limits on car testing to gain an unfair edge in next week's race in Arizona.