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The pair are part of a group of seven men who have competed in all the individual full-distance Challenge Wanaka triathlons.
''They kind of make a bit of a fuss about us,'' Mr Smoothy, of Brisbane, said.
He and former Dunedin man Mr Simpson, who lives on the Sunshine Coast, have both finished 39 Challenge, Ironman and other long-distance triathlons worldwide since 1990 and 1995, respectively.
''To get to 40 is like, where did that come from? What insane person does that?'' Mr Smoothy said.
Yet the men have no plans to call it quits, with Mr Smoothy's sights set on at least 10 more.
''As long as I can still finish by the cut-off times, I'll keep going.''
Mr Simpson said while his body allowed him, he, too, would continue racing. Mr Smoothy's love of the sport is partly about ''chasing that elusive perfect race'', which he had experienced just three times.
The thrill of simply finishing was unbeatable, Mr Simpson said.
''I think no matter how bad a day, how long you take, coming up that finish chute ... the crowds cheering you on, it's like an adrenaline rush.''
Challenge Wanaka rates among the best events for the men, who compete in an average of three long-distance triathlons a year.
''You come here and you feel like you're with family,'' Mr Smoothy said.
''The local people, you see them set up in their front yards. They'll have a barbecue or a beer and they'll be out there for six or seven hours cheering people on. It's just lovely things like that that make this event special.''
Wanaka provided one of the toughest courses in the world: ''You don't come here for a PB.''
Mr Simpson has had 51 starts in long-distance triathlons. Among his DNF [did not finish] efforts are two Challenge Wanaka races - one he attempted with gout in his foot, the other when he came off his bike at 90kmh and ended up in hospital.
Mr Smoothy has been in more than 300 triathlons and his one DNF at a race in China ''shattered'' him: ''But I went back the following year and finished it.''
He hopes to finish today in under 12 hours - his fastest time to date is 10hr 21min.
Mr Simpson's personal best is 12hr 55min and he is aiming for under 15 hours.