35 Years of Ironman Stats: Bike Aerodynamics

In this installment we return to the curious case of the Kona bike splits. We previously enquired why the (male) athletes aren’t putting more power on the cranks today than they were ten years ago. Power is only one aspect of the equation, though. As every modern triathlete is all too aware, aerodynamics play a vital role. That should provoke curiosity.

Without diving through the equations for wind resistance, we can still see a difficult mathematical relationship: if the two driving factors behind finish time are aerodynamics and power, and both power and time have generally remained constant for the last 10 years, should we really believe claims that the bikes have improved their aerodynamics?

We received several unsolicited responses on this and other matters with regard to Kona. Theories run wild, and with the permission of some of those who wrote in we explore their suggestions.


Let’s first deal with the most obvious point of contention– drafting. Several pro athletes wrote on condition of anonymity that drafting is rampant in the pro ranks, even at the front. Norman Stadler and Chris McCormack almost went to blows over accusations of cheating in 2007, and Faris Al-Sultan also accused McCormack of cheating on the bike. If nothing else, there are at least strong and passionate suspicions even among the top contenders that not everyone plays fair.

That being said, there needs to be a discussion of what is and isn’t fair. Right off the bat, it should be said that for our purposes here, “drafting” is meant in the context of an aerodynamic phenomenon, not gaining unfair advantage in a race. Whatever rules WTC and USAT decide, ultimately it’s science that determines where drafting occurs.

I have personally written in the past that the USAT and WTC draft boxes are too big for their own good. Based on research in the 1970’s by cycling pioneer Chester Kyle, I’ve argued that we should cut 2.5 meters off the USAT draft box. There does exist experimental data indicating Kyle and I might be wrong, though. That data comes from a velodrome; not necessarily representative of Kona conditions but definitely more “lifelike” than a wind tunnel.

WTC officials have been operating on the basis of a “secret drafting rule” at Kona for years, as cogently reported by Triathlete‘s Aaron Hersh in 2012. Head official Jimmy Riccitello believed there was a definite aerodynamic benefit at 10 meters, which motivated him to extend to 12. But if widening the gap was meant to further negate the benefits of drafting, it’s remarkable that neither the bike splits nor the associated average power outputs have varied much since then.

If they were drafting before, does that mean they’re still drafting now? Even if they are, continuing to widen the gap may cause another problem– the power surge required to execute a legal pass within the allotted time. The farther back you are off a guy pushing 280 watts, the longer you have to push close to 300 watts to get by. Make the gap too wide, and you force the athletes into a position where it makes more sense to stay where they are. Swim position then locks up the bike leg. So it’s possible that you can’t completely get rid of drafting. We may have reached the “best possible case.” Whether you’re an athlete or an engineer, there’s plenty of fodder to chew on.

If there really is an aerodynamic benefit to be reaped at 12 meters then some items seem less debatable. The first is that those who swim fast, bike fast. Whether there are genuine aerodynamic benefits of being in the lead group out of T1 or it’s a placebo effect we can’t be sure. But it’s rare that we see a contender ride up from fifth to first place and then continue apace to open a 30-minute gap on their pursuers. Do the athletes draft or do they simply lie in wait to strike from T2?

Just because the mental game playing out on the road can’t be quantified doesn’t mean we can discount it. One pro with Kona experience wrote “If you come out [of the water] in the big front group, it’s a huge advantage. But that’s also why those guys tend to ride similar power. Guys of similar build in a group riding the same speed are going to generate roughly the same power.” And what of the placebo effect?

“People like to talk about the “X-factors” [like] pacing, etc. But that’s mostly because it makes a good story. That for sure matters near the end of the race, when you’re really tired. Coming back in from the airport when the group is broken apart, the psychological advantage becomes significant. But the bulk of what I’m talking about here is aerodynamic benefit.” The frontrunners’ tendency to convoy out of T1 and hang together for the whole day has become affectionately known as “the Hawi express.”

Lead Moto

A phenomenon unique to the race leader may validate that suspicion. Pros with firsthand experience relate that they feel a distinct aerodynamic benefit from the camera motos following the race. It’s assured that those motorbikes aren’t always respecting the 12-meter rule, so the spotlight offers its own aerodynamic advantage. But if that’s the case, then the leader isn’t likely to push as high a wattage as they normally would. And if the second, third and fourth cyclist behind them exhibit the same power output as someone who is definitely (though unintentionally) drafting, then our confidence that those pursuers are also drafting is likewise increased.

The fact that power outputs have been as consistent within the ranks of the top ten as they are in a pro tour peloton for as long as wattages have been published strongly suggests that drafting is indeed happening from the front all the way to the end of the line.

Again, there’s a distinction between the rules of man and the rules of mother nature. It’s therefore possible that physics masks an important strategic principle from our statistical analysis– the swim really does matter. Last one out of the water gets a rotten deal. This isn’t meant to be a discussion about fairness or legality. Rather, it’s about the physical limits. Whether by accident or intent, drafting is drafting is drafting. It doesn’t matter if you’re trying to cheat your fellow athletes or not, no one can cheat the laws of physics.

Those motos are always going to be there whether we like it or not (and we do). The concern is how those conditions influence the race. What if the pro event in Kona began in a time-trial format, with individual athletes spaced five minutes apart? Would they push higher power yet take longer to finish?

Race Tactics

One former racer-turned aero engineer for a major manufacturer commented that such a format might actually inspire pro athletes to become better cyclists.

“It amazes me at how little professional time trial tactics actually exist 33 years into your focus on our sport.  Example:  Do you know what percentage of finely coached athletes know what I’m talking about when I suggest having a “cue sheet” of key elevation gains taped to their stem or aero extension?  Approximately ZERO.  Are they well trained cyclists?  Most, yes.  Do they know how to race?  Very few.”

But that begs the question, why would you need a cue sheet if your race strategy is to pace off the two or three guys in front of you? So the Ironman bike course– and not just Kona, but all courses– is a unique species apart from UCI legal bike races. It’s actually one of the enjoyable things about Ironman.

Ironman races a different way, and consequently has catalyzed the development of a different kind of athlete. Likewise, we have our own unique bikes. Being unbound by the worst restrictions the UCI puts on bike designs, tri-specific bikes like the Shiv and the P5 get signature design features we love, to say nothing of frames like the Dimond and Ventum.

Which brings us to another important consideration when discussing aerodynamics at the front of the pack. What about the bikes? The helmets? The wheels? The shoes? Did it ever really matter, or were all those “every second counts” advertisements just a bunch of pseudo-science hooey? That question brings us to a kind of safari through triathlon’s wild kingdom– a dangerous trek through the mountains of positive bike reviews and into the dark jungle of CFD and wind tunnel data where people are allowed to know certain things if only they promise the information will never leave the room. In our next installment, we go on the hunt for a rare species of bike that is seldom seen and even less frequently discussed. We go on the hunt for the elusive aero pig.

If you enjoyed this analysis of Ironman bike stats, check out Part 1 (overall performance) and Part 2 (swim) and Part 3 (bike) and Part 4 (bike power) and Part 5 (run).

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photo credit: 123 (13) via photopin (license)

About the Author

Jim Gourley is the author of Faster: Demystifying the Secrets of Triathlon Speed and The Race Within: The Story of the Ultraman Triathlon. He is a regular contributor to Tom Ricks' blog "The Best Defense." His work has been featured in Men's Health, Stars and Stripes, and several triathlon and cycling publications.