For most of the previous 15 stops on the AMA Supercross tour, the athletes and their mechanics have had it relatively easy.

Saturday, during almost 10 hours of racing at Rice-Eccles Stadium, there will be something missing at the competition.

Oxygen.

Until today, the superstars of the motocross world haven't had to compete on a course higher than the 1,100-foot elevation of Phoenix's Chase Field.

The dirt laid on the Rice-Eccles Stadium floor starts at 4,657 feet above sea level, and if tour leaders James Stewart and Chad Reed expect to continue their dominance over the field, their crews will have to figure out how to get every possible ounce of power from the engines that will be starved for combustion-fueling oxygen along the Wasatch Front.

"The conditions are going to be tough," said Andy Short, currently third in the series standings, "so it's going to be exciting."

The scarcity of oxygen will affect the way the motorcycles are able to power up and around the course. There might be less big air, and if riders are not able to get enough speed, there might be fewer triples and more doubles, with an extra jump added to mix things up.

"Out machines are going to be a little slower because of the lack of air," Short said. "It's going to change tactics ... but your instincts take over once the gates drop."

Add the threat of rain and what some precipitation might do to the track over a few dozen races before the main event, and there will certainly be some on-the-fly improvisation as the races progress.

One thing is certain, though. All eyes will be on Stewart and Reed as they try to get a leg up on each other heading into next week's series finale in Las Vegas.

Stewart jumped into the lead with a second-place finish last week in Seattle, while Reed struggled to a rare seventh-place finish. That result gave Stewart, the reigning series champion, a slim three-point lead over Reed.

"We've already put last weekend behind us. It was a disappointing result but what's done is done, and we're focused on getting the job done properly in Salt Lake City this Saturday," Reed said. "There is no real margin for error — it's a two-way race as it has been all season, and the rider that is hungriest for the title will win."

Stewart, who failed to win a race in which he did not crash for the first time in 54 races last week when he placed second, is happy to be back on top but knows he's far from secure.

"Chad's been riding great all year," Stewart said, "So for me expecting to get off the podium (with the points lead) was kind of one of those things that you had to be lucky."

AMA Supercross

Today, Rice-Eccles Stadium

TV: CBS, Sunday 10 a.m.

12:30 p.m. — Supercross Lites qualifying.

1:45 p.m. — Supercross qualifying.

3:20 p.m. — Supercross Lites qualifying.

4:20 p.m. — Supercross qualifying.

7:30 p.m. — Supercross Lites heats.

7:50 p.m. — Supercross heats.

8:10 p.m. — Supercross Lites last chance qualifier.

8:20 p.m. — Supercross last chance qualifier.

8:40 p.m. — Freestyle motocross exhibition.

9 p.m. — Supercross Lites main event.

9:30 p.m. — Supercross main event.

E-MAIL: jeborn@desnews.com