The 255 Triathlon launched

 The world’s longest single-day triathlon, the 255 Triathlon, is set for August 2021 at Goodwood

what is the longest single-day triathlon in the world

The first of its kind, the 255 Triathlon is set to become the longest single-day triathlon in the world in August 2021. Designed by TriBourne Multisport Events to “push the limits of human endurance and mental stamina,” the event will take place at Goodwood Motor Racing Circuit, West Sussex, located near Portsmouth.


The unique format will see athletes taking on a 5km swim (4 laps) in nearby Westhampnett Lake, then hopping onto the bike for a 200km ride (52 laps) around the racing circuit, before setting off on the final run leg, a mere 10 laps adding up to 50km around the circuit’s perimeter. The total distance? A whopping 255 kilometres, all powered by the human body, in one day.

Race director Matthew Dowle says: “Ironman has always been widely regarded as the ultimate single-day endurance event. Now it’s the time to introduce the next step for endurance triathletes. 255 Triathlon will not only push competitors to a new level of physical and mental endurance but will also provide an unparalleled level of engagement for spectators throughout the whole event.”

The organisers also hope that the motor circuit will provide the perfect opportunity for supporters to spectate and cheer on the ultra-endurance junkies from the pit lane as they complete lap after lap of the traffic-free, flat course. Each athlete will have access to their own personalised nutrition box in the pit lane, as well as additional aid stations.

Live commentary, lap split timings and music will add to the atmosphere. The inaugural event will be limited to just 300 entrants, who will be racing against the clock with a tight 18hr cut-off time. Do you think you have what it takes to complete this ultimate feat of endurance? You can sign up at

Get a head start on your endurance training and check out our useful triathlon training, mental strength, and nutrition sections.