They've shown they have the speed. Now they will show if they go the distance.

Beijing Games bronze medallist Emma Moffatt and fellow Olympians Brad Kahlefeldt and Peter Robertson will step up to half-Ironman distance racing this Sunday at the Geelong Long Course triathlon.

The trio have all made their careers in Olympic distance events, which consist of a 1.5km swim, 40km cycle leg and 10km run.

Olympic-distance triathletes usually make a smooth transition to long course, which on Sunday is a 1.9km swim, 90km cycle and 21.1km run.

But Geelong will feature a strong field of established long-course triathletes and Moffatt knows she is in for a tough initiation.

"I have no idea what prompted me to enter - I guess it's something I've never done before so it's a great challenge and a good way to prepare for my upcoming World Championship Series races," Moffatt said.

"The furthest I've done in a race is Olympic distance and I still enjoy the ITU races so, in the near future, they will be my focus.

"Maybe in years to come, I will do more longer racing.

"It is going to be an interesting day - I'm actually really excited to race. Doing something new is refreshing but, come race day, I'm not sure I will be overly excited."

Sunday's long-course race will include defending champion Clayton Fettell, Luke Bell, Leon Griffin, Tim Berkel and Chris Kemp, who all have impressive credentials.

The woman to beat will be Melissa Hauschildt, who has won the world title at this distance, with Australian Ironman champion Michelle Gailey also in the field.

Moffatt and Kahlefeldt raced at the London Olympics, while Robertson's glittering career featured three Olympic-distance world titles and selection for the Sydney and Athens Games.

Robertson has been training in Thredbo with the formidable squad run by Australian coach Brett Sutton, which features star Ironman-distance pair David Dellow and Caroline Steffen.

Dellow and Steffen are preparing for the March 24 Ironman Asia Pacific championship in Melbourne.

The Urban Long Course race is part of a packed triathlon program for the weekend's Geelong Multi Sport Festival.

Sunday's program will also feature the ITU Oceania Cup, which doubles as the Australian sprint-distance triathlon championships.

Last year's breakthrough Noosa Triathlon winner Peter Kerr and London Olympian Emma Jackson will headline the sprint race, which is a 750m swim, 20km cycle and 5km run.