Last year, he came in second in the Tour of Italy, despite riding most of the race with a fractured shoulder. He gritted his teeth so hard to overcome the pain that he had to have 11 of them recapped.
Today he is up with the leaders in the Tour de France, this time with a fractured collarbone.
"There may be a few more trips to the dentist in my future," Hamilton wrote in his race weblog last week. "It was pretty gritty out there."
Hamilton's story of determination has become almost as compelling a subplot in the Tour as the main theme: Can fellow American Lance Armstrong win his fifth consecutive Tour? While Armstrong's skills have earned the respect of the French hosts, Hamilton's courage has won their hearts.
"Of the 200 or so riders who started the race, there's only one that would have continued with Tyler's injury," says Stephen Pucci, who coached the Massachusetts-born cyclist when he began his career. "The other 199 would have packed up. Does he have a higher pain threshold? It's hard to say. Is he more determined? I'll bet you on that."
Hamilton was injured on the first day of the Tour, in a massive pile-up just before the finish line. X-rays revealed a V-shaped fracture to his right collarbone and his race appeared to be over almost before it had begun.
But at the press conference that evening when he was due to announce his withdrawal, he could not bring himself to utter the words after dedicating the last 11 months of his life to training for the Tour. Heartened by the arrival of his wife, Haven, and their golden retriever Tugboat, he decided to stay in the saddle.
"This guy is as tough as nails," says Steve Madden, the editor in chief of Bicycling magazine. "I'm absolutely amazed."
Hamilton came late to cycling, after an accident during student ski training forced him off the slopes.
"He had tremendous ability, but he didn't seem like an incredibly serious athlete," says Pucci, who manages the CCB-Volkswagen cycling club with which Hamilton rode as a youth. "He was very concentrated, though, and didn't get down, didn't suffer about what didn't happen."
"He is extremely determined but he has always held on to a level of fun, too," adds elder brother Geoff Hamilton. "He was big into skiing and cycling, but he was doing lots of teenage stuff other cyclists wouldn't. He didn't get all serious about cycling till he was in college."
Hamilton turned professional in 1995, and drew international attention as one of Lance Armstrong's lieutenants on the US Postal team, helping his leader win three Tours de France and reaching higher up the rankings himself each year.
In 2002, he switched from US Postal to become the leader of the Danish CSC team.
"Lance wasn't going anywhere, and Tyler was thinking: Do I want to end my career but never realize my full potential?" says his brother.
As CSC team leader, Hamilton has begun to fulfill his potential; after placing second in the Giro d'Italia last year he finished 15th in the 2002 Tour de France.
Earlier this year he won the prestigious Liege-Bastogne-Liege race, and commentators began to talk about him as a dark-horse contender for this year's Tour de France, rivaling his old mentor Armstrong.
But success has not gone to the 32-year-old American's head, say people who know him well.
"He was a nice, polite young man and he's the same today," says Pucci, who is deeply proud of his former protg. "He's a humble, straightforward, honest kid. You could sit next to him on an airplane for five hours and you might not even know that he is a bicycle racer."
He may be self-effacing, but he is determined. When he first heard the results of his collarbone X-ray, "I didn't quite know how to react," he wrote in his weblog.
"It felt like someone had sucked all the air out of the room," he continued. "At that moment, the Tour was over. I felt like I was walking through a nightmare."
The next morning, however, to the astonishment of other riders and the hordes of journalists covering the Tour, Hamilton took his place at the starting line, his chest tightly strapped to hold his collarbone together.
"I had to prove to myself that I couldn't ride," he said later.
But he could ride, at least that easy stage across flat countryside. So he decided to stay in the race to support his teammate, Carlos Sastre, who had so often worked for Hamilton to give him victories.
"Cycling is a team sport, and the Tour de France is our Superbowl," he explained on his Web site. "Just about the worst thing imaginable to any rider here is to have to face going home and leaving their team behind to finish a job they should have been part of."
As the days have passed, and Hamilton has kept up with the leaders even through three punishing days in the Alps, he has set his sights higher.
"Making it through the Alps changes everything," says Team CSC manager Bjarne Riis. "Tyler is one of the favorites on this Tour. He's doing better and he's looking good on the bike."
Not that he feels much better. The pain "hasn't subsided very much, it's more like I'm just starting to get used to it," Hamilton wrote on Sunday.
Now, few people on the Tour expect him to pull out, and some suggest he may even be on the podium in Paris, one of the top three finishers.
"I have to expect anything from my brother now," says Geoff Hamilton. "I get goosebumps watching him, and I can't stop smiling."