Kasey Kahne, Ryan Newman out

Editor's note: For an explanation of the Rule of 72, click here.

It's that time of year when many people are asking me: Who is left in the Chase for the Sprint Cup? Which drivers still have a chance?

To answer that now that we're four races into the Chase, let's pull out my Rule of 72 formula we've used for the past two seasons to determine who has a shot at the title going into the last race.

According to the Rule of 72, drivers are eliminated when their total points or total finishes accumulate 72 points or more.

So, the first driver eliminated from contention using this formula is Kasey Kahne, with a score of 77 after only four races. His first four starts in the Chase have resulted in no top-10 finishes, which surprises me because Kahne finished third in points last season. He hasn't shown that form to date.

With only one top-10 finish in the Chase so far, Ryan Newman finds himself on the outside looking in with a score of 69. Although just short of 72, it appears to be too great a deficit with only five races until the final event at Homestead-Miami.

Moving up the Rule of 72 standings, the next group of drivers still in contention for the 2013 Sprint Cup, Clint Bowyer, Dale Earnhardt Jr., Carl Edwards and Joey Logano, all have serious work to do. With total points already in the 50s, each of these drivers needs consistent top-five finishes to take a step back from the cliff's edge.

Greg Biffle and Kurt Busch are better positioned, but only marginally.

Closer to leaders Matt Kenseth and Jimmie Johnson in the Rule of 72 standings are Kyle Busch, Jeff Gordon and Kevin Harvick. Top-five finishes this weekend in Charlotte would keep them in the game. And while a top-10 finish wouldn't be disastrous for these three, a poor finish or a DNF would be.

Of course, it would help Busch, Gordon and Harvick immensely if Kenseth and Johnson had an off day. But Kenseth and Johnson haven't had off days since the Chase began.

Kenseth, the Chase points leader, and Johnson, a mere three points behind, have been outstanding so far. They've combined to win three of the opening four races, with Kenseth finishing first at Chicago and New Hampshire and Johnson taking the checkered flag at Dover.

Starting with finishes of first, first and seventh, Kenseth established himself as the guy to chase in the Chase. But after last weekend's 11th-place finish at Kansas, the No. 20 team needs to regain its opening momentum. To be a champion, you need to demonstrate resilience. I expect to see that from Kenseth this week at Charlotte.

Johnson entered the Chase with four consecutive finishes of 28th or worse, which left a lot of people scratching their heads. But the No. 48 team has performed like the champion that it is, turning in four Jimmie Johnson-like outstanding races to start the Chase. The bad news for the competition is that historically, Johnson is at his best in Chase races five through seven.

So while I believe seven drivers still have a legitimate chance at contending for this year's title, they all need to be concerned by the start Kenseth has had and that Johnson is in his typical late-season form.