The hardest IRONMAN 70.3 World Championships ever?

IRONMAN 70.3 World Championships 2025 course preview

This year, the IRONMAN 70.3 World Championships take place in the Spanish seaside town of Marbella. 2025 is the year of “Carbs before Marbs” and you’re going to need it in order to get round this monstrosity of a bike course – with 20m of climbing per kilometre it’s got to be the hardest 70.3 World’s course in history. The course map really doesn’t look that bad but it has 1.5 times the amount of elevation per mile than the “mountainous” IRONMAN World Championships course in Nice – it’s way harder. Of course, myWindsock is the only acceptable tool to quantify exactly how hard this course is.

The course doesn’t look too bad on paper as the climbs are quite low altitude, but there’s steep pinches and it starts right at sea level so it’s a tough slog up to the peak at 600m.

The hardest thing about this course is the fact there’s long climbs with vicious pinches in gradient that peak over 20%. We can look at the gradient plot and distribution of gradients here.

Using the two myWindsock gradient plots, we can see that riders spend the majority of their time between 3 and 9% – moderate gradients, however the trouble comes above this. For most riders to keep their cadence over 80, they’ll need a gear ratio of at least 34-40. There’s likely an argument for a gravel rear mech at this race to allow a much larger cassette and still maintain a decently large front ring for the descent.

How to think of the course?

The course leaves Marbella toward the hills behind it, passing Palo Alto, Ojen and surrounding villages to a turnaround – where you go back on yourself a couple of times before descending into Marbella itself. The most likely scenario is a stiff wind blowing off the sea helping you up the first climb before a more open section where anything could happen!

This might be the hardest 70.3 World’s there will ever be – in order to get prepared properly myWindsock is the only place to nail your pacing, planning and post race analysis all in one subscription.