Dale Earnhardt Jr. and other NASCAR drivers and crews are battling high winds and periods of rain at Las Vegas Motor Speedway, in a crucial week of testing for NASCAR.

Two days of Sprint Cup testing at the 11/2-mile track on the northern end of Las Vegas Boulevard will be followed by two days of testing at the two-mile California Speedway, three hours away.

And make no mistake — this week of testing is all about the car. Earnhardt, the fastest overall in speed during Daytona testing, said that NASCAR’s stocker “is the 800-pound gorilla in the room that’s just going to take a while for us to ‘science’ out and understand.

“And we ain’t really had a whole lot of laps because of the weather.”

One key to getting the car around these two fast tracks is figuring out how to get as much downforce as possible on the nose, to help the car turn. The car simply doesn’t turn very well, so crew chiefs are pushing the limits. The front bumper, called a “splitter,” bottoms out, making the car a handful.

“When the splitter gets on the ground, the car goes up the track,” Earnhardt said. “So you’ve got to get that splitter off the ground, but as close as possible, to get the maximum downforce.

“It’s a real fine line trying to adjust those two things. It’s hard to have one without losing the other.”

The reason NASCAR has added the splitter to the car is to keep teams from running expensive, soft springs. But solving one problem only presented another.

Earnhardt said that last year’s model “traveled”; that is, the nose dropped down to the asphalt, with the softer springs, to make the car more aerodynamic and turn better at high speeds. At California Speedway, for example, NASCAR stockers routinely hit 208 mph going into the first turn.

“Now you got that splitter — it don’t go nowhere; you can’t grind it off,” Earnhardt said. “You need to get the car traveled down as much as you want … but then the splitter touches the ground and it’s terrible. Blows the whole corner. So it’s a challenge.”

At least Earnhardt has cousin Tony Eury Jr. as his crew chief again to help him get this challenge figured out. Eury moved from DEI to Hendrick Motorsports last fall, to pave the way for Earnhardt at his job.

While the Earnhardt-Eury combination is a familiar one, the Earnhardt-Hendrick relationship is still being formed. Hendrick said that Earnhardt has deferred to his teammates, Jeff Gordon and Jimmie Johnson, at every opportunity, which has impressed Gordon.

“I’m just taking it in,” Earnhardt said. “I’m listening to what they’re saying, trying to find out what kind of drivers they are and how serious they are about their work, trying to learn how to be around them … and what they want from me, what they’d like to know from me.”

Earnhardt certainly knows why to defer to Gordon.

“The first time I met Jeff I was at North Wilkesboro practicing for a Late Model race,” he said. “We happened to be there the same weekend as the Cup cars.

“Dad walked up and introduced me to Jeff, who was sitting on the pit wall. That wasn’t really the first time I’d met him; Dad introduced me to him when he was in the Busch series (in 1991, when Earnhardt was just 15).

“But he introduced me to him again at North Wilkesboro. Dad never introduced me to people. So for him to be doing that, I figured there was something important going on, some reason I needed to know this guy.

“Jeff was winning championships when I was just getting started. He’s had a little bit to do with guys coming into the sport at the age they’re coming in now — to see him challenging, winning races, beating guys five or 10 years older.

“I thought I should already have been in the series…. I was a late bloomer, got a late start. I was upset with myself for not pushing myself to be in the sport quicker, instead of goofing off so much.”