Over the years, many of Brennan's loyal friends have coalesced into a group of bike riders who call themselves the Geezi (that's plural for geezer, they explain). Many don bright orange team jerseys with, in Brennan's honor, a shamrock dotting Geezi's final "i", when they meet in Woodside three days a week to ride. The group makes it to the coast and back on Saturdays and does slightly shorter Tuesday and Thursday rides.
While the ages of participants range from the lower 60s to Brennan's 87, the rides are far from pleasure jaunts.
"Most of (the other riders) are not very nice on the long rides," Brennan says. "They make me suffer. They make me work," he says. "They push hard, and they make me push harder."
Although he's known to utter "I hate you, I hate you" to riders who pass him ("in a kind way so no one's harmed or offended," says Geezi teammate Millo Fenzi of Woodside), Brennan realizes his fellow riders are on his side. And it's not just that they encourage him to ride directly behind them, where the phenomenon known as drafting means he won't tire as quickly.
Exceptionally nice people
"You couldn't find kinder people in the universe," says Brennan of those he rides with and their families.
"They are exceptionally good, and exceptionally nice, people," he says.
That was proven on a sunny Saturday in late June, when a group of Geezi and their support team pushed Brennan into riding 200 kilometers (just about 125 miles if you don't speak metric) with 8,800 feet of climbing thrown in.
The ride, which its organizers called the Bay Area Wicklow, was an attempt to cheer Brennan up after, for the first time in at least 18 years, he couldn't ride in his native country's Wicklow 200 because of his wife's ill health. The 200-kilometer ride, with 8,800 feet of climbing, takes place in County Wicklow, Ireland. The event's website calls it "Ireland's oldest and for many the toughest single day challenge bike ride" and "one of the toughest challenges in Irish sport."
Since a Wicklow 200 competitor who was three months older than Brennan retired in 2012, Brennan has been feted each year as the oldest competitor to finish the grueling ride.
"He had the guy assassinated," teases fellow Geezi Steve Lubin of Woodside about the older rival.
Lubin can tease Brennan because the two of them have been racing each other on their bikes since 1962 (56 years ago), when Steve was 13 years old. Brennan, Lubin says, "was ancient — he was practically 30" that year as Lubin came in first and Brennan second in the Pescadero Road Race.
"That is where the rivalry started," says Thalia Lubin, Steve's wife and sag wagon driver who provided food and water along the route of the Bay Area Wicklow.
Teen road racer
Brennan starting racing competitively in 1947 while still a teen in Ireland. "I was never very good," he says. "My claim to fame in racing was I was one of the guys who got dropped, which means you got left behind by the faster guys, and made the faster guys look good."
He raced for six or seven years, "and then I met my wife and that kind of took over from racing," he says. "Although I still rode a bit."
"Bernie claims he still rode a lot," Fenzi says.
Shaun and Bernie married in 1956.
Brennan was a journeyman woodworker, building elaborate wooden railroad coaches out of oak, ash, teak and mahogany, but was persuaded by his sister to give living in the United States a try.
On May 22, 1959, Shaun, Bernie and their 2-year-old son, Ciaran, arrived in Palo Alto. Four days later, Brennan started working as a cabinet maker.
In 1967, Brennan, by then an American citizen, went to work for United Airlines doing building maintenance, carpentry and locksmithing. He rode his bicycle from his home in Belmont, where he still lives.
He retired in 1994. And even though he's had bicycle accidents that resulted in a fractured skull and broken collarbone, and he once "hit a fencepost and took the nose completely off my face," he's never quit riding.
After one of the mishaps, Brennan says, riding friends had a T-shirt made with the ambulance crew's radioed-in description of him: "Elderly gentleman in excellent physical condition."
Nowadays, the Geezi try to look out for Brennan's safety. "Bernie's looked me in the eye and told me I'm personally responsible for his safety," Fenzi says. "I take that seriously."
Be like Shaun
The other riders in the group seem to be somewhat in awe of Brennan. "We all say we when we grow up we want to be like Shaun," Fenzi says.
"We want to be Shaun," Lubin adds.
"It gives us something to aspire to in our golden years," Fenzi jokes.
Brennan says there's no real secret to his achievements, other than his support team.
"I just ride and enjoy the riding," he says. "You just do it."
Lubin says that "tenacity has something to do with it."
But Brennan says it's simply not giving up, even mentally. "If you say you can't do it, you've given up. There's a lot of people older than I who possibly could do the same thing."
He admits, however, he couldn't do it without his teammates. "To do what we do, you need the support of these guys, whether it's in your mind or physical," he says. "When you meet people like this and they ride with you, it does encourage you and gives you extra help in staying up."
Plus, says Fenzi, "the best time to perk up Shaun and get him feeling energetic is for him to see a slower, 'wounded' cyclist in front of him."
"It's like a shark scenting blood in the water," Fenzi says.
Eight riders completed the entire Bay Area Wicklow with Brennan: Kim Freitas of Atherton, Laura Stern of Menlo Park, Steve Lubin of Woodside, Joel Kaplan of Redwood City, John Woodfill of Palo Alto, Mark Clifford of Los Altos, Larry Bolander of Pacifica and Malcom Plant of Berkeley. More than a dozen other riders rode part of the way with the group, with about 20 riding at the end.
The group left at 5:30 a.m., with Fenzi on his Vespa at times blocking traffic for the riders, on a route that took them through Pescadero, Santa Cruz and Los Gatos as well as several Peninsula cities as the temperatures reached into the 90s. They ended back in Woodside with a celebratory barbecue at the Lubins' home.
Brennan was presented a medal and a certificate for finishing, similar to those he's received for the Irish ride.
"It was a lovely course, and a lovely day, and great company," Brennan says. "It made me feel good; it made me feel like I was doing the Wicklow."
Aiming for more
Brennan does have a goal he's reaching for. It seems that last year Robert Marchand of France retired from riding after setting a record for riding approximately 14 miles in an hour in an indoor velodrome, at age 105.
"That's what I'm aiming for," Brennan says. "When I'm 105 I'm going to beat his record," he said.
He won't be doing it alone, though.
"I need all these guys to help me."