BMX, mountain bike preview

We've divvied up the four Olympic cycling disciplines into two families: old school and new school. Here's a look at the more newfangled, off-road, fat-tire disciplines, BMX and Mountain Biking.

An offshoot of motorized dirt biking, this pedal-powered version of the sport made its Olympic debut in Beijing. On smallish but sturdy bikes, helmeted, comprehensively armored riders will make their frenetic way around a track roughly a quarter-mile long laced with berms, banks and corrugated "whoop" sections designed to ensure they spend as much time hurtling through the air as they do on terra firma. Crashes are common.

After a seeding phase in which riders take an individual lap, races switch to a mass-start format. After three runs, the best two riders from each quarterfinal progress to the semis, which also follow a three-run format. Top four riders from each semifinal advance to the final, where the medals are decided over one run.

Connor Fields, U.S.: 19-year-old from Las Vegas nearly quit the sport after a knee injury sidelined him in 2010. His coach, Sean Dwight, snapped Fields out of his funk over the phone, according to the New York Times, telling the 19-year-old, "I'm going to say this once. You have the ability to win the Olympic Games." After coming back, Fields won three straight World Cup races this season, and has an exceptionally hot hand going into London. Looks like Dwight was right.

Magalie Pottier, France: The gifted, versatile Anne-Caroline Chausson won this event in Beijing, then graduated to coach of a super-strong French team whose top rider is Pottier, a former junior world champion from Marseille who most recently won the BMX world championships in Birmingham, England.

British BMX rider Liam Phillips will line up at the start of the men's BMX event despite snapping his left collarbone cleanly at the Worlds in Birmingham in May. "I had surgery and it was plated," he told BBC News, "which means I can get back to training almost immediately."

Aug. 10: Men's and women's gold medal

On the Olympic program since 1996 in Atlanta, mountain biking features a mass start, followed by riders making multiple laps on a rugged, technical course (think narrow, rutted, roots, rocks) featuring at least one nasty climb. The circuit at Hadleigh Farm, in Essex, east of London, is 5.1 kilometers, and features 210 feet of climbing per lap. Officials will decide the number of laps just before the race, which will last around two hours.

Julien Absalon, France: One of the few (if not the only) mountain biker in the world with his own dedicated fan club, the 31-year-old won gold in this event in 2008 and '04. During that stretch Absalon also took four straight world titles ('04 through '07) -- one of the most dominant stretches in the history of this sport. He's cooled off a tad, settling for bronze in the 2011 world championships, but still has to be considered the favorite at Hadleigh Farm. "I don't win all the races," he says. "But I win the good races."

Catharine Pendrel, Canada: Grew up on a horse farm in New Brunswick, where her brother, Geoff (now an elite downhill MTB racer) carved trails into the hills behind their house. Pendrel, 31, finished just off the podium in Beijing (fourth), but has looked very tough lately. She is currently No. 1 in the world rankings and won the world title last season. No less encouraging to Canadians: she won the Olympic test event at Hadleigh Farm.

No American has medaled in this made-in-the-USA sport since Susan DeMattei took bronze at the '96 Games in Atlanta.

Aug. 11: Women

Aug. 12: Men