A decade ago, many NASCAR Sprint Cup Series drivers would shrug off the sport’s two summer road course stops with a mentality of endure and move on. The bulk of the races were won by only a handful of racers proficient in skill and positive in attitude.

Nowadays — and particularly since the Chase for the NASCAR Sprint Cup playoff format began in 2004 — drivers can’t afford to take mulligans in the road course events. The events are too important to the championship run, when a race victory could mean the difference between a Chase berth or a long autumn.

And even if they haven’t completely embraced the style of road course racing, drivers are at least preparing themselves better.

Teams hire road racing “specialists” to prepare the cars and drivers have self-enrolled in driver schools.

Stewart’s teammates Ryan Newman and Danica Patrick, along with Matt Kenseth, recently prepped during a private test session at the Virginia International Raceway road circuit as did reigning Cup champion Brad Keselowski, who also turned right at Road Atlanta.

Richard Petty Motorsports even used one of its official NASCAR test dates this season at Sonoma for drivers Aric Almirola and Marcos Ambrose, who is already considered one of the sport’s best on road circuits.

The new focus on this style of racing has produced a diverse roll call of A-students.

Defending Sonoma winner Clint Bowyer is a former dirt late model racer. Kasey Kahne, the 2009 Sonoma winner, came up through the USAC sprint car ranks as did two-time winner Stewart and the course’s all-time best, five-time winner Jeff Gordon.

“I think the cars are so good now, and the drivers have gotten so good and have come around to road racing a little bit better,’’ said Roush Fenway Racing driver Greg Biffle. “I think those things are some of the reason why everybody is so competitive, and in fact, we see oval track guys like Clint Bowyer and myself and others that run really good at road course races. The road course ringers don’t seem to do as well anymore.’’

For all the effort and hype the road course “ringers” would get for their twice-a-year, win-or-nothing entries, the last time a non-NASCAR regular won a Sprint Cup Series road course race was 30 years ago — Mark Donohue at the former Riverside, Calif., circuit.

Canadians Ron Fellows, a sports car champion, and 1995 Indianapolis 500 winner Jacques Villeneuve are crashing the party this weekend.

“A few years ago, all of the rage was the ‘road course ringers’ that they would bring in to these two races, but they never seemed to have the success you would have thought,’’ said Penske Racing driver Joey Logano, who in 2011, became the youngest Sonoma pole-sitter at age 21.

“I think that’s because the regular guys that are out here, they are some of the best race car drivers in the world, and we’ve all been able to adapt to racing on the road courses better and better.

“Now I feel like we can all compete with each other, and we are as good as any of the ringers. I feel the same way about myself. I have a lot more things I can still learn, but I have worked hard and gotten a lot better over the years.’’

For those, like Logano, success has been as much as attitude as aptitude.

Add to that the debut of NASCAR’s new Gen-6 car, and the competition feels as wide-open as it’s ever been. Gone are the days of Gordon’s dominance or even heavy favorites.

Not only have there been no repeat winners in the last eight Sonoma races, but last year, seven of the 12 Chase contenders also finished outside the top-10 there, showing how deep the field of talent really is.

“It’s sort of weird how it transitioned,’’ Biffle said.

“Before these road course ringers could come in and be super-competitive, be a lot faster than the NASCAR guys. I think two things have happened. One, the car technology has gotten much better, so the cars are much better, and the driver cannot make up as much difference using that skill set he has for road racing only.’’

Stewart refers to it all as the natural “evolution” of the sport.

“The fun thing is you look every year and that list (of contenders) keeps growing,’’ Stewart said.

“That’s a compliment to our sport that the teams and the drivers are taking road course racing that much more seriously. That in itself makes it more fun. You do have more guys that are capable of going out there and being a contender at the end of the race.

“Who would have thought Clint Bowyer would be in contention last year? Kurt Busch sat there with a car that was broke and drove to a third-place run.

“There are guys out there now that do a really good job and the list keeps growing. You can’t just sit there and pick one guy that you say would be a factor. You’re picking the same number of guys on a road course as you would on an oval on a weekly basis. And that’s making it a lot of fun.’’

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