Britain was once the epicenter of the bicycle industry, and it has a racing history that dates to the 19th century. But its racing scene, while extensive, has mostly been domestic and heavily based on time trials, the individual race against the clock, partly because of police and government resistance to permitting races on public roads.  Over the years, many British riders went elsewhere in Europe and often found considerable success. But it was a lonely and unsupported calling.  Roger Hammond, whose career mostly spanned the 2000s and who is now a team director with Dimension Data, recalled receiving a less than enthusiastic greeting upon his arrival across the English Channel. Given that professional cycling had hardly been a sure thing for British riders, he completed his university degree before giving it a try.  “I remember leaving my house in a Vauxhall Nova, sleeping two nights in the car, trying to find a professional contract,” he said Sunday over the din of the engine of his team’s enormous white bus. “We didn’t really have a heritage of good bike riders coming from the country, so I was just another foreign rider.”  He did find a contract, but for much of his career, he and Jeremy Hunt were the only Britons racing at the highest levels in Europe, and they received little notice back home.  “It was pretty hard to get a nation captivated by two little Brits in Europe who were lost in big teams riding for other people,” Hammond said.  That has changed completely. Now there is not only a clear career path for good British riders who want to turn pro but also a demand for their services from European teams. And cyclists, both men and women, are celebrities in Britain. Their sport is not just popular; it is fashionable.  “Now we have heroes,” Hammond said. “The British public became captivated by the sport of cycling.”  The key building block of Britain’s success was a program developed by Dave Brailsford, who went on to establish and run Team Sky. Starting out with money from a national lottery in 1997, the program focused on scouting and recruiting physically gifted youths, regardless of whether they had any cycling experience. Just as important, it also concentrated on track racing.  The result was something of an Olympic-medal-making machine. At the most recent Summer Games, in London, 12 of Britain’s 65 medals came from cycling, eight of them gold.  Brailsford’s approach sometimes had its critics. Although track racing was immensely popular during most of the first half of the 20th century, even in the United States, it now generally attracts attention only during Olympic years.  Cummings, 35, said he had always been interested in the road rather than the track. But he also acknowledged that the British track program, which was in its early phases when he started, had set him on a route to the Tour. When he was in his late teens, he said, the idea of becoming a road pro “was kind of almost beyond a dream.”  He added: “I had to go on the track. The track gives you the ability and the funds to be a full-time bike rider, which is what you need.”  The success of Brailsford’s program has brought more money and further broadened its programs. There is an academy for the best 16- to 18-year-old riders in the country who are looking to turn professional on the road. Grants allow others to test themselves on foreign amateur teams. Interest from sponsors has led to the creation of a number of second-tier professional teams in Britain, which dart into and out of the Continent for races.  Demand for young British riders has also created options for the most talented. Rather than attend the academy, McLay, 24, accepted a team’s offer to apprentice in the bare-knuckle world of Belgian cycling.  “It suited me better,” he said after giving a young boy an autograph near the start on Sunday. “I like to do things my own way, or whatever, rather than being told what to do or being mothered.”  Johnny Weltz, a retired Danish rider who is now a team director at Cannondale-Drapac, an American team, said many Americans were not ambitious enough when they came to Europe.  “l understand it’s difficult because you have your family far away, it’s an extremely difficult sport and you get more often beat up than you get success,” said Weltz, who has worked for several other American teams in the past. “What I see often with Americans is, they do fine, then they come up to a point where they say, ‘O.K., I’ve done what I was dreaming of, and now it’s time to bail out at a young age.’ I’d like to see them be more persistent.”  Weltz said he believed the sport had yet to become a significant part of the sports culture in the United States, despite increased participation and interest in road cycling.  LeMond, who does analysis for Eurosport, a European cable channel, credited U.S.A. Cycling for having established several successful development programs, and he pointed out that several talented Americans were now racing. But he has long preached that a major effort to develop the sport broadly — particularly among teenagers — is also needed if the United States wants British-style success.  “Imagine if U.S.A. Cycling encouraged grass-roots racing; imagine if you try to encourage road racing, cyclocross and mountain biking through building programs at schools,” LeMond said Monday in the air-conditioned comfort of a motor home near the finish line. “If you get kids at that age interested in cycling, you’d tap into a tremendous amount of talent.  “All it takes is five good riders to change things.”  An earlier version of this article misstated the number of Americans in this year’s Tour de France. There are five, not four.  A version of this article appears in print on July 20, 2016, on page B11 of the New York edition with the headline: British Riders Dominate as Americans Fall Behind. Order Reprints| Today's Paper|Subscribe
British cyclists are dominating this year’s Tour — an unthinkable achievement not long ago. For the United States, things are trending in the opposite direction.