''I always say the less clothes you've got on the better it is because you stay cooler on the bike and run. I'd race naked if I was allowed to,'' Reed said laughing, going on to point out the reason behind his chequered briefs. ''I like the idea of checkmate as you run past people.''

A record and sellout field of more than 1500 triathletes have registered for Sunday's event, one of Australia's final headline triathlons of 2012.

Reed's anticipated rematch with Australian champion Tim Berkel is off. Berkel was a late-withdrawal for the race after holding off Reed at October's Australian 70.3 championships. But Reed doesn't expect to have Sunday's race all his own way, with 2010 champion Ollie Whistler and youngster Joseph Lampe among his main rivals.

Lampe, who finished second to multiple world champion Terenzo Bozzone at last month's half ironman in Shepparton, punctured on the bike leg while leading in Canberra last year.

''He's still young so he's still improving every race, and he's one of those guys you don't know whether he's going to be in flying form or have a shocker, he's a bit unpredictable,'' Reed said.

Even if 27-year-old Reed defends his title on Sunday, he may not be back in Canberra again.

With Australians a dominant force in ironman triathlon racing, Reed intends to step up to the full 3.9km swim, 180km cycle and 42km run next year.

''As I move to ironman distance racing and focusing on Hawaii for next year, I don't think I'll be able to race it again, so I was really keen to do it one more time,'' Reed said.

''I think it's one of the toughest races in Australia for this distance. It really spreads out the packs on the bike and it becomes a real solo effort which means, at the end of the day, the fittest guy tends to win as opposed to the most tactical racer.''

The course has been altered because of safety concerns, removing the hilly terrain on the bike course along Coppins Crossing. Defending women's champion Lisa Marangon, who is expected to battle with Canberra's Michelle Wu for victory, urged organisers to crack down on competitors illegally drafting on the flatter bike course.

''Because it's all flat and multiple loops, I really hope the drafting is monitored because I know for a fact that I can ride stronger than anyone else that's there and every time I get caught in a race, it's usually from someone drafting off another person and catching me on the run,'' she said.

Marangon and Wu can also expect strong competition from Kate Bevilaqua, although one of the pre-race favourites Rebekah Keat has withdrawn.

''I'm excited, I'm not scared of anyone that's coming to race,'' Marangon said.

''My goal for 2013 is to be the 70.3 world champion in Las Vegas, that course suits me.''