It is difficult to choose a single hardest Ironman event, as it depends so much on an individual’s ability. If someone struggles in the heat, they will crumble on a course known for its heat, while if someone is allergic to steep climbs on the bike they will have a very different preference.
I’m going to break down some of the world’s toughest IRONMAN branded events. The Xtri events are all probably harder than every single one of these, but the IRONMAN brand draws hundreds of thousands in each year, so I’m going to go focus on these.
IRONMAN Lanzarote
This race is legendary for many reasons. The fact it is one of the first events in the European season makes it fiercely competitive for a start, with hundreds looking to stamp their ticket to Kona early, so they can rest and then start a build towards the World Championships once they qualify.
Firstly up we have a two lap 3800M sea swim in water temperatures that average in the high teens. Being in the Atlantic rather than the Mediterranean, the chances of a choppy swim are higher than most races in this part of the world.
Coming out of the water into a chilly morning where the air temperature is similar to the water temp, you are onto arguably the world’s most legendary bike course. The fact that when I did IRONMAN UK in 2019 it was pronounced as “having even more elevation than Lanzarote” probably tells you all you need to know.
However, it’s not simply the 2550M of elevation gain over nine separate climbs that make this course one of the hardest in the world, it’s also the brutal winds that hit the island off the Atlantic. Not only are these winds strong, they are also unpredictable. You may think that a headwind on the way out means a tailwind on the way back, but you may find that the wind direction has completely changed, and you have to battle your way home through a cross headwind.
Europe is renowned for its tough bike courses, but this legendary bike route really is a cut above the rest.
The run is the most straightforward part of the event, but the conditions can swing between warm with a light breeze to incredibly humid from year to year. So if the winds are on your side on the bike, this may come back to bite you on the run as you find yourself running a marathon in hot, humid air.
This course will be especially challenging for those whose bike skills are anything short of excellent. Another factor to consider is that given its place in the calendar,
IROMAN Wales
At the opposite end of the spectrum is Ironman Wales in Tenby. Every leg of this classic event will push you hard, there is a reason that the event sells out so fast and attracts athletes from around the globe.
You start with a sea swim prone to strong currents. In 2024 one of my athletes cruised at 1:40 per 100M for the first 400M, then dropped down closer to 3:00 per 100 after turning at the first buoy. He had to repeat this for both laps. Every sea swim can be unpredictable, but Wales is famous for pushing even seasoned professional athletes to draw on every piece of talent they have just to make it out of the water some years.
With no less than 23 steep hills to ride over, the bike course at Tenby, the bike course at Tenby is legendary. Making up 2400M of elevation over the 180KM, you need to make sure you bring a pair of strong bike legs to this event. Those who do all their training on the turbo in ERG mode need not apply.
Not only do you have the bike course to contend with, there’s also the Welsh weather. With temperatures as low as 14 degrees some years, the combination of driving rain and howling winds has forced hundreds of perfectly fit individuals into the back of the broom wagon as they just can’t face the relentless nature of the elements. Appropriate clothing and experience riding in adverse conditions are essential.
In most events, once you make it off the bike you are most of the way there. With 42.2KM to run. However, Wales has a whopping 500M of elevation on the run, which will force most athletes to a walk at numerous points.
If you’re an athlete who is likely to be flirting with the cutoffs, you will most likely end up running the marathon in the dark. Back of the pack swimmers may not enter the water until 8AM, and with sunset around the 7PM mark, this will leave many tackling arguably the hardest marathon on the Ironman circuit in the dark.
Despite the brutal course that will make you question all of your life choices that lead you to this moment, the support is second to none, which is what keeps bringing back athletes time and time again.
IRONMAN World Championship
The original IRONMAN race is still one of the hardest on the calendar. The course itself is not the most challenging, but what makes the event so difficult is the combination of wind and humidity.
Stepping off the plane and into the Hawaiian air feels like walking into a steam room. The air feels oppressive and it’s impossible to escape from. To make matters worse, you have to run an IRONMAN in these conditions.
The race starts with a single lap out and back swim, where wetsuits are always banned. 3800M with no rest and no wetsuit is enough to make the blood of many triathletes run cold on its own.
Once out of the water and onto the bike, athletes then tackle the 180MM rolling bike route which is famous for its crosswinds. So much so that disc wheels are banned. While the 1700M of elevation gain pales in comparison to the other courses on this list, the wind and humidity make it a force to be reckoned with in its own right.
Without a doubt, the toughest part of the day is the run. A 42.2KM run at the hottest part of the day in one of the most humid places on the planet. What could go wrong?
Even with ice buckets at every aid station and athletes using every trick in the book to cool themselves, the complete lack of shade, and complete isolation on much of the run course.
The course is legendary, and its place in IRONMAN history unmatched, but expect it to push you to your absolute limit.
IRONMAN Nice
The controversial split between the men and women’s field between 2022 and 2025 bought the World Championship to Nice. It was chosen due to both its history in the sport as well as the challenging nature of the race.
The event begins with a 3.8KM sea swim in the calm, warm waters of the Mediterranean. Athletes could be forgiven for getting lulled into a false sense of security at this point, but the bike course is where the race comes into its own.
The bike route covers over 2500M of elevation gain, putting it in the same ballpark as Wales and Lanzarote, but the difference here is the length of the climbs. These are not short hills you can power over in a few minutes, Nice has you riding up mountains.
The biggest mountain is a whopping 28KM long, covering 1200M of elevation gain. Along with the physical challenge of riding up this mountain, you also have the fast, technical descent down the other side to grapple with as well.
Thankfully the weather does not tend to be especially hot, humid or windy, so the mountain rather than the elements are your biggest battle.
Once you are off the bike it is a flat run along the coast with minimal shade. With temperatures averaging the mid 20s however, you are unlikely to cook. The fairly average swim and run are still bookends to an incredibly challenging hike course, which is what has earned this race a spot on this list.
Conclusion
There are plenty of other extremely challenging IRONMAN branded events on the calendar. Some have an extremely challenging year when the route designers get a bit carried away, but these are the most consistently difficult courses on the calendar, providing a challenge to every competitor year after year.
If you are taking on one of these events, you cannot afford to simply hope for the best, there’s a reason the DNF rates at these events is so high. Check out our IRONMAN programmes here.
