The Red Bull Trans-Siberian Extreme is the longest bicycle road race in the world, a grueling endurance test of 14 stages that unfurl over 5,700 miles from Moscow to Vladivostok.

The distance is so great that riders pass through seven time zones. They roll over roads through forested hills, along highways clogged with trucks. They spin along pavement, cobblestone and gravel, and through meadows as vast as the eye can see.

For this year’s race, eight men and two women set off from Moscow’s Red Square on July 18. They have dropped out one by one, and by Monday, there were just three remaining: Pierre Bischoff of Germany, Aleksey Shchebelin of Russia, and Marcelo Soares of Brazil. On Wednesday, these three will begin the 14th and final stage, pushing to be the first to roll up in front of the opera house in Vladivostok, a port city near the border with China, on Aug. 14.

Even before the race is done, organizers are reflecting on a separate challenge: how to get more women to take part in the event next year, and how to keep them in the race longer. This year was the first time that women entered as solo competitors, and neither of the two female riders, both accomplished endurance athletes, got through half of the 14 stages.

Women are a minority in the world’s endurance bicycle races, and some of the competitions tailor their rules by gender.

Such is the case with the Race Across America, a trek of about 3,000 miles from California to Maryland in which 20 percent of the cyclists are women. Rick Boethling, the executive director of that race, said organizers have slightly different rules for men and women. If male riders do not complete the race in 12 days, they are listed as “did not finish,” meaning they can keep riding if they wish but they are no longer officially part of the race. But female riders are given an additional 21 hours.

“Historically, if you look at athletics, there is a difference between male and female competitors,” Mr. Boethling said. “So effectively we have given them almost a full extra day to finish, and that is based off other events and other sports comparing top men to top women.”

The Trans-Siberian race, in its third year, is trying to make the event more attractive to female athletes, but Paul Bruck, the race organizer, said in an interview on Monday from Russia that the next steps were not clear.

One option could be to have women participate in two-person teams instead of solo, which would allow them to hand off and get more rest. This year, both women, Shangrila G. Rendon and Thursday Gervais Dubina, failed to meet required average speeds of 13 miles per hour and fell behind on recovery and meals between stages.

“We just would like to have women in the race, and we think it is more logical to have a dual team of women,” Mr. Bruck said. “They can be as fast as solo men.”

Ms. Rendon, a 35-year old Filipina-American who holds the Guinness World Record for the Quintuple Ultra Triathlon, said she struggled with lack of sleep, saddle sores, cramps, bad weather including hail and roads thick with trucks.

“I was able to last, kind of survive,” she said. “It was extreme. It is definitely something I have never experienced.”

Alone after Ms. Gervais Dubina left the race, Ms. Rendon eventually fell too far behind the remaining men, who were in a pack and drafting each other. The start times were the same for everyone, but the men invariably finished stages sometimes hours ahead, meaning the women had less time for recovery, massage and food, she said.

She dropped out officially after the sixth stage, although she tried to power through the seventh.

“I did my best to hang on with the guys, but statistically we do know men are much faster,” she said. “A lot of times I would end up riding on my own.”

While she said she had an overall “great experience” at the race and praised its support teams and organization, she suggested rules could be improved by giving women earlier starts and more time to complete a stage across a shorter route.

But Mr. Bruck ruled that out. “In this race we have a pretty strict timing and cannot organize two races,” he said. “This would be logistically impossible.”

Ms. Gervais Dubina, 48, a competitive cyclist from Bloomington, Ill., said she dropped out partly because of “horrendously dangerous” road conditions.

“I had three instances where head-on traffic was coming straight at me on the shoulder,” she said. “It just got too much for me, so I pulled out.”

Like any true battle, there were supply line considerations. Mr. Bruck said 27 vehicles — including one designated for each rider — tagged along with medical supplies, food, parts and other support. When riders could not keep up with the food cars, meals were delivered to them, he said.

Ms. Gervais Dubina said sometimes the support vehicles clung to the pack of men in front, rather than the stragglers. At one point the traffic was so bad she came to a standstill because the van dedicated to accompany her could not make it up the shoulder of the road.

She said one mistake she made was not having proper food, sometimes consuming only race gels or fruit. And while the first three stages were fairly flat, in the Siberia region the terrain was hilly and the roads rough.

“If I was mentally stronger I probably would have stayed in longer,” she said. “I think this game is 90 percent mental, truthfully.”

Ms. Gervais Dubina, an artist and cancer survivor, said she has been cycling for most of her life and competed in triathlons. She trained more than a year for this race.

“I wasn’t going to be fit enough to stay up with the men, and I knew it,” she said. “Women just can’t finish these races in the same time frame as men. I knew that going into the race.”

But she wanted to do it anyway, she said. “I threw myself out there as a guinea pig.”