Which Is Harder: The Ironman World Championship or Leadville 100 Mountain Bike Race?

Ironman Kona vs. Leadville 100. We ask athletes who have raced both and offer tips for success at each.

These two iconic races are held in locations that are worlds apart. Both races have reputations for being extremely difficult and have been known to break the hearts and minds of the athletes involved. We wanted to know: Which race is harder?

Ironman World Championship

The Ironman World Championship race is affectionately known as “Kona” and is held on the Big Island of Hawaii. The town of Kailua-Kona, Hawai`i, hosts the event where participants swim 2.4 miles in the ocean, ride 112 miles along the beautiful coast and through the barren lava fields. Racers finish by running a full marathon (26.2 miles). Temperatures can often reach 90-95 degrees Fahrenheit (F) and the humidity averages 85% in October (when the race is typically held). Combined with the brutal winds of the Big Island, these environmental wild cards always play a role in influencing the outcome for all triathletes.  

Kona is steeped in triathlon history, with the first race held on the island of Oahu in 1978. Though the course and the timing of the event has changed a few times over the years, the distances have remained the same. For the very first time this year, the race will be held over two days with the women’s race taking place tomorrow, October 6, and the men’s race on Saturday, October 8. 

To be considered an official finisher, racers must complete the entire course in less than 17 hours. There are cut-off times within the race that must be considered as well. Athletes must complete the swim in 2 hours 20 minutes after their start wave. The swim, first transition (T1) and the bike must be completed in a total of 10.5 hours. The remaining 6.5 hours, to total 17, is for the second transition (T2) and the run.  

Swiss athlete Daniela Ryf owns the female course record at 8:26:18 while German Jan Frodeno has the male course record at 7:51:13. 

Leadville 100 Mountain Bike Race

In sharp contrast to the warm, sunny beaches of Kona, the Leadville 100 Mountain Bike Race (LT100) is held in the high mountains of Colorado. Race start is at a lung-searing 10,152 feet and the course takes riders up to Columbine Mine at some 12,550 feet. Total elevation gain during the race is approximately 11,000 feet. In a cruel twist, racers expecting to be near the finish line when their bike computer turns over 100 miles will find that course changes over the years have pushed the total race distance to some 105 miles. However, course cut-off times have not changed. Temperatures on race day can be in the low 30s (F) at race start. A roll of the dice determines if race day will be hot and dry or rainy and cold with hail and driving rain pelting racers trying to climb and descend tricky sections of the course.  

Like Kona, LT100 was once a mass-start event. Now both races have wave starts. Kona start waves are age-based while LT100 wave starts are based on qualifying event times. In Leadville, racers must cross the timing mat at Twin Lakes Outbound four hours after their respective wave start. Twin Lakes Return must be completed within 7 hours 45 minutes. Athletes must finish in under 12 hours to be considered an official finisher. The last official finisher receives the coveted “Last Ass Up the Pass” trophy.  

Annika Langvad owns the women’s course record at 6:59:24 and Alban Lakata owns the male course record at 5:58:35. 

So which race is harder?

To determine whether racing Kona or the LT100 is harder, we sought the expert opinions of 12 athletes who have completed both races. The race resumes of these athletes are extensive, some of them are former professional athletes and others have completed both races multiple times. Several of them have achieved podium performances. What they have to say might surprise you… 


While preparing for Leadville can require some serious training volume, your efforts are solely focused on one sport versus three, as Seth Graham said: “I think having race fitness in three sports and managing to peak at all three at the same time is harder than peaking in a single sport.” And then there’s the not-so-simple fact that juggling the training for three sports requires some adept time management (especially if you want to keep your job and family life intact), as Graham said: “Training for Ironman is more time intensive than just training for the bike and requires a lot more scheduling and understanding from work and family.” 

Perhaps it is training for a single sport that lulls triathletes into a false sense of confidence, especially those who have previously completed Ironman events. As Joy Rasmussen, who raced Kona in 2008 and LT100 in 2019 and this year, said: “The first time I did Leadville I may not have taken it seriously. I didn’t understand the magnitude of the legendary race, the required training I was about to embark on and the altitude gains that would test my physical capabilities and performance beyond any triathlon.”  

Yet others trained more for the LT100 than Kona, like Sara Bloom. She raced Kona in 2019 and raced LT100 this year. She said: “Kona took me about an hour longer to complete than LT100. I feel like I raced each of them to the best of my ability. Nothing catastrophic happened either day. I trained harder and more consistently for longer for Leadville. With all that said, Leadville was still harder.”  

Cut-off times and DNF rates

Both Kona and the LT100 have time cut-offs during the race, which are 17 hours and 12 hours, respectively. Both men and women need to make the time cuts, regardless of the known physical differences in performance.  

Graham said: “The cut-offs are way more aggressive in Leadville, while Ironman cut-offs are pretty soft. I have a friend that finished Kona and DNFed Leadville twice. A true comparison would be to make the Kona cut-off 12 hours and see what happens to the field.” 

James Parks raced Kona in 2014 and Leadville this year. He agreed: “The DNF rate of Kona when I did it was 6%. According to the 2022 Leadville results page, 1,016 cyclists finished prior to the 12-hour cutoff while 1,375 started the race. This is a high 26% DNF rate.”  

Spot-checking a few years at LT100, the DNF rate ranged between 26% this year to as high as 37% in 2005. According to Cole Chlouber, community manager for the Leadville race, the average DNF rate is 30%. The calculated DNF rate for Kona is 7% (according to runtri.com). The difference between DNF rates between the two events is obviously significant. Is this the clear marker for which race is more difficult?  

Pick your poison: heat and humidity or altitude?

At both events, environmental conditions will always influence race results. It has been well studied that as temperatures and humidity increase, endurance athletic performance decreases. Athletes aiming and pushing for a certain race time or placement can easily find themselves in trouble. Even if you’re just looking to finish, heat and humidity can derail your day.  

RELATED: How Do You Succeed at Kona?  

Bloom said: “You can be the best athlete in the world but if you can’t handle heat, Kona will destroy you.” Todd Murray, a five-time Kona finisher from Colorado, agreed: “One of the reasons that Kona was harder than Leadville for me was the heat and humidity in Hawaii. I would always take cool temperatures and altitude over Hawaii’s heat and humidity.”  

Many studies have shown that how well you handle altitude can be determined by genetic factors, and that’s something Cathy Yndestad found worked in her favor: “The Queen K in Kona, although iconic and rich with history for triathletes, is not as beautiful as the iconic mountain climbs of the Leadville 100. I’d choose altitude over extreme heat and humidity any day.”  

Where you live and train can have an influence on your ability to cope at altitude, of course, but there are no guarantees, even for those who are well acclimated to higher elevations. Plenty of Colorado residents have trouble at LT100. Perhaps a combination of genetics and hometown is beneficial, as Aaron Acuna, who raced Kona in 2014, 2019, and is racing again this year, said: “The altitude definitely plays a part. Luckily, living in Colorado, I didn’t feel like it was as much of a factor for me, but I imagine others coming from lower elevations may have struggled more.”  

RELATED: Is There a Benefit to Altitude Training?

Race day

It can often take a “magic day” for success to come at either Leadville or Kona, but pushing your limits on race day is not without its risks. As Bill Steen said: “When I tried to race Ironman all-out, it would simply crush me by the time I got very far into the run. Biking 112 miles (and trying to race) takes a real toll on your legs before you even start running. The marathon was typically a death march—not only physically but mentally it was extremely difficult too.”   

Many other athletes agreed that Kona race day is harder, largely because of the scorching heat on the Queen K during the marathon. However, for those looking to complete versus compete at Kona, it’s a race that (if handled correctly) can be easier to manage from a pacing point of view. As Rasmussen said: “In Kona, there are times in the swim, bike, and run where you feel the need to get into your groove and go at a pace that can be easily managed due to heart rate or power training. Trained athletes have the skills necessary to know when to back off in each of the three disciplines. In Leadville, there is no opportunity to back off.” 

In Leadville, racers compete for the best bike line on all the climbs. Going off that best line, at minimum, can cost extra energy and in the worst-case scenario it can mean a race-ending crash. Aaron Acuna said: “Spending 9+ hours on a mountain bike with your body jostling around, navigating rocks, roots, other people and ruts takes a serious toll on your body throughout the day. There is a serious need for the mental focus needed to remain upright and not crash. This is why the LT100 is more difficult in my opinion.”  

Some athletes also said there’s far more that can go wrong at Leadville, although there’s still plenty that can go awry on the Big Island. Rasmussen added: “So I think that people who do races like Kona, where you can work a plan and follow numbers, could have a hard time wrapping their head around Leadville where things change, mechanicals happen, and the race doesn’t develop like a podcast or coach has led them to believe.” 

Fueling for success 

Controlling speed or intensity on race day is only part of the challenge, as all endurance racers know. Managing nutrition is often far more challenging and it is not unusual to have your GI system revolt. Sara Bloom said: “I actually threw up my nutrition on the bike during Kona and never had to stop moving forward, just kept on pedaling. There are aid stations every seven miles on the bike. During the run if you are super tired, you can walk the marathon to keep moving forward and finish, and there is an aid station ever mile. For me, managing nutrition seems harder in Leadville because aid stations are sparse. For a 10-hour race we had four aid stations and two water stations.” 

Conclusions and takeaways

Of the 12 athletes we spoke to, 50% said Leadville was harder, five said Kona was the toughest, while one was undecided. Regardless of whether you’ve raced both, one, or neither, we’ve compiled a few key takeaways for anyone looking to succeed at either of these two legendary endurance events:


Be prepared for all kinds of weather: Rain or shine, there’s never any real way of knowing what the Colorado mountains might throw at you. Make sure you and your crew are prepared for all weather eventualities. 

Respect the altitude: There’s less oxygen available for you to push the pace—and even for those who are extremely well-acclimated to training and racing at elevation, it can still do funky things to you. Prepare yourself as best you can and understand that pushing your body past its limits at higher elevations can have big consequences.  

Know the course: From knowing the best lines to take to knowing where best to fuel and recover, those who do their homework and know the course well stand the very best chance of success.  


Stick to your plan: If you’ve prepared well then you should know exactly what your body is capable of (think power, pace, heart rate). Don’t suddenly expect these numbers to be higher or better on race day. Stick to what you’ve done in training and remember that the heat and humidity will inevitably slow you down. Those who pace themselves carefully in the earlier stages of the race will be the ones moving the best in the latter miles of the marathon.  

Fuel and hydrate well: Did we mention it’s hot and humid in Kona? You have to be diligent about what you’re drinking and eating. You simply won’t make it to the finish line at this race otherwise.  

Respect the island: Kona can be a brutally tough place to race. Those who forget that are often reminded in the harshest of ways. In the words of former Kona champion Sebastian Kienle in a recent interview: “You come here, you think you are somebody. The island shows that you are nobody.” 

Gale Bernhardt has coached Olympians and professional and recreational endurance athletes for years. Some want to go faster, some want to cross the finish line, while others simply want endurance sport as a lifestyle. She provides ready-to-use, easy-to-follow training plans for cycling and triathlon.