Crowded Ironman Courses and Bike Packs

You’re riding well, down on your aerobars, when a pack of triathletes engulfs you, what do you do? Sit up and drop back the required 12m then do the same when the next pack comes along; work hard to go back round and ride off the front, only to blow up later in the ride; or do you sit in, maintain your pace, perhaps even take a turn on the front? Pictures from Ironman Melbourne (if you haven’t seen them, look here) would suggest this dilemma was faced by most age groupers at some point during their day. But it is a problem that extends beyond one race: with increasing numbers of athletes crowding courses the formation of packs seems almost unavoidable.

In simple numeric terms if you have a 12m drafting zone, as they did in Melbourne, then you can fit roughly 83 perfectly-spaced athletes in a 1km stretch of road, with a field of 2000 you need around 24km to correctly fit everyone in. The process of legally overtaking may mean exact distances vary, but basically it takes a lot of road to space out that many athletes. So when you shorten the swim element of a race effectively bunching the field closer together, a crowded bike course is guaranteed.

Why the Course is Crowded - The Number of Athletes Exiting T1 Per Minute in Melbourne

The impact of the shortened swim is quite obvious when you look at the number of athletes leaving T1 at minute intervals. In 2012 there were fewer competitors and a full distance swim, at no point were more than 50 athletes leaving transition during the same time frame. In 2013 though, with higher numbers and the reduced swim distance, transition peaks with 100 athlete all leaving in the same minute interval. It may have been necessary to shorten the swim, but the crowded bike course and formation of packs that followed was inevitable.

Less Crowded at the T2 Entrance at Ironman Melbourne

By the time the athletes return to transition the numbers have changed, as the graphs above show the rate is much lower (each column now represents a 5 minute period). The bunching that we saw at T1 has diminished and groups have generally split. The pattern is a little denser in 2013 than in 2012, so it appears they haven’t broken up as much, but this may be due to the larger field. Packs formed early in the race when the swim failed to separate the competitors, 180km later groups have tended to disperse and spread; there is little evidence of strong pelotons working together for the entire course.

Diminishing Crowds - Comparing Athlete Counts per 5 Minutes at each Bike Timing Mat at Ironman Melbourne

There were timing mats every 45km in Melbourne and I can use that data to look a little more closely at how the groups dispersed. The graphs above allow easy comparison of each split. By 45km the density seen at the exit of T1 has significantly diminished with a peak of 208 athletes in a single 5 minute window; this continues to drop, peaking at 162 at 90km, 123 at 135km and 81 at T2. All good signs that packs were generally separating. I think it’s reasonable to say that the majority of those who found themselves caught in a bunch due to the density of competitors at T1 were likely riding clear by the end of the bike. Of course there will have been some who choose to draft, but this is a much harder contingent to assess. Timings of athletes at static points on the course reveal little of the overall dynamics of the race, simply being close to another athlete at a timing mat does not mean you were drafting.

I am experimenting, examining groupings of athletes over consecutive timing points and identifying those who maintain close proximity across the course. Too raw to give numbers from and it has its flaws: it can’t distinguish a legal pace line from a team time trial, nor could it spot an opportunistic drafter who jumps from athlete to athlete. Post hoc drafting identification will never be possible, but perhaps there is a way to compare groupings on different courses. With more work I may be able to suggest which courses see the highest rates of pack formation, I suspect it will correlate with number of athletes. In the meantime, for the curious, the chart below gives the athlete density at T1 for all the 2012 Ironman races.

Athlete Density: How Crowded are the Ironman Courses at T1 Exit

Drafting will always be a problem, there are always those willing to cheat, but the density of athletes on a course amplifies this by drawing in those who might otherwise ride honestly. If you left T1 surrounded by dozens of other competitors, would you feel it was your obligation to drop back or theirs?

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  • Lachie

    It’s all well and good to determine how much drafting there was based on objective data, however, I was out on Eastlink at the 80km mark of the bike and I can safely say that there was more people that I have ever seen blatantly drafting. These people weren’t forced to sit there, they were actively working to sit wheel and sitting in packs of 20-30. I feel sorry for those front pack age group swimmers who rode legitimately fast times but were smashed in the marathon by others who were able to ride circa the same time, if not faster, on much lower average watts

  • Lachie,

    As I said you can’t actually measure drafting through a few fixed timings on a course, all I can really look at is density of athletes as a course as one potential indicator of the levels of drafting. In Melbourne early in the race this is certainly a contributing factor, at T1 exit the only way to avoid people effectively drafting is to have them queue to leave at 12m intervals, even supposing you allowed a 5km zone to spread out, people would have to partially soft-pedal the first 5K to achieve the spread. I’m certainly not defending those who chose to draft quite wilfully, more pointing towards the issue of race crowding as a contributory factor to levels of drafting.

    The bunches you saw were cheating and in part taking advantage of strength in numbers making it difficult for the TOs to apply penalties when there are too many in a group to easily do that. Thinning out the density of athletes on the course would make it harder for large bunches to form and easier for the TOs to fairly apply penalties.

    The worst drafting I ever encountered was at the first Ironman 70.3 World Championships in Clearwater. At the far turn around, 45K or so into the bike, the group was so big I had to put my foot down and wait my turn to go around the bollard! I had tried riding off the front, working far too hard, only for the bunch to swallow me up again, I tried sitting up and dropping back only for the next bunch to swallow me and have to do the same again, by that turn around I gave up and rode back easy letting people pass me by. Worse race experience I’ve had. They spent subsequent years trying to fix the issue through wave management, never quite got there from what I heard, a tougher course like Vegas is proving better. I also feel sorry for those mid-pack swimmers who are strong on the bike they’re unable to have a clear path to the front of the field, I was never front of pack on the swim, but I could bike myself up that way.

    In an ideal world no athlete should choose to cheat in a race, but given we know it happens course design or waves can be used to spread athletes out more and make it easier to detect and manage drafting. I’m not offering those athletes an excuse for riding on wheels, perhaps I’m suggesting that they may not have planned to draft, but felt ‘everyone else was’ – that’s no excuse though.


  • Stuart J

    Sadly some of the worst drafting I’ve seen is in the PowerMan Duathlon series where (at the time and things may have changed) there seemed to be little policing or respect of the 12m rule.

    That said, is 12m enough? An interesting study here suggests perhaps not. (sorry I cant add a hyperlink.

  • Stuart J

    Actually it seems I can add a hyperlink 🙂 Sorry about that!

  • I’d heard, although not read, about that blog post on the drafting affect at 12m – 20W power saving is pretty significant at Ironman, that’s going to be a roughly 10% saving at the front of pack I’d estimate, which could make a huge difference over time.

    Of course the real difficulty would be if you expand the drafting zone further you also make the process of managing drafting harder – I’d expect larger drafting zones to generally result in more people drafting – intentionally or not. Again it’s a congestion issue too – a crowded course makes big drafting zones near enough impossible to manage, at least until the latter parts of a race. I doubt we’ll ever find a perfect solution, or eliminate drafting in the sport, but I do feel there are steps that could better manage the issue such as wave starts and using course design to attempt to split athletes early.

    Thanks for the link,


  • Sammy

    Simple answer is to ban the sport.

    It’s become a watered down sob fest.

    Like running, Ironman and Triathlon have died the death of mass participation. Lifestyle sports were never meant to be hard…. not nowadays anyway.

  • Nick B

    I always come out of the swim in the top 30 overall as an ex county swimmer and spend the next 3 hours being overtaken by the bike packs already mentioned. Even worse as a decent swimmer, you don’t always get a draft in the water either!! Lachie’s fears are correct. Wales this year was the worst, with many nationalities cheating even on a non favourable drafting course like Wales. Some of these guys even had matching kit, so it was clearly part of their well rehearsed race plan. It’s not the organisers fault but I only saw one marshall on a bike the whole day. The risk / reward ratio for cheating, not worth worrying about.

    My view is that we need many more draft busters at the sharp end of the race where the Kona slots are coming from. I don’t think it really matters if someone wants to cheat their way to a 20min faster time at 15+ hours.

    Wave starts? Not convinced Russ. The 2 wave starts at Wimbleball was a joke last year. When it got to the run you did not have a clue if you were 15 mins ahead of the guy next to you or racing them, especially when they hide their age group code letter as an additional cheat.

    Bottom line, any law not enforced by anyone is likely to be ignored. I wonder what would happen to the crime rate if the police had a holiday now and again? I think the WTC should put some traffic wardens on a bike and give them an incentive to catch as many cheats as they can…problem solved do you think!?

  • Nick,

    You will only reduce drafting by making it more difficult to draft – i.e. more policing to follow your crime analogy. But the marshalling of the course, or specifically the number of draft busters is going to be up to the organisers to an extent – they could certainly request, place and fund more on the day.

    But crowding is a problem, again with the crime analogy, it is easier to police a small group of 10 than a large group of 100, the latter was the case for the packs in Melbourne. 100 athletes in a group creates a huge problem for a draft buster: you can’t physically issue a penalty to them all, stopping them has potential risks too, plus any group penalty may unfairly penalise the odd athlete caught by that group. The dynamics at that scale are different to Ironman Wales and the form of drafting that you witnessed there.

    I wouldn’t use the UK 70.3 as a good example of drafting, the counter to that would be Roth that has manage far more athletes and waves successfully for many years. There are easy ways to get round the problems of identifying age group – writing it on the individual has never been perfect, all it took was some suntan lotion to have the number wash off anyway, these days it’s covered in compression gear. Race Numbers or wrist labels could be colour coded though as a means of identification, I’ve seen that done in races. On multi-lap races it’s not always been clear to me what lap someone in my age group is anyway, so it’s not always clear when you’re racing head-to-head, I’ve just assumed if they’re in front I want to be going past them!

    To cut down drafting you need more draft busters – those numbers are up to the organisations that put on our races (along with the governing bodies) – but for draft busters to be effective there is a limit to the number of athletes they can handle at any one time, it’s something else organisers can address through their race design (the course, wave starts). In the Melbourne example when 200 people leave T1 within 2 minutes that’s a lot of people close together on the road and going to be hard to thin out. It’s not a panacea, when I raced the initial 70.3 champs in Clearwater the drafting was terrible despite a wave start – The course was too easy and the waves were poorly structured and ordered.

    Yes, athletes need to stop drafting too. Plenty say they don’t, but clearly in the heat of the race a lot of them will. I think premeditated, blatant drafting is relatively rare (as in sitting inches off a wheel consistently), probably a handful per race, but I also think there’s a lot of soft-drafting: not dropping back the full distance when the persons wheel overtakes; initiating a pass, failing and dropping back; slotting into a legally spaced group rather than overtaking the lot; not overtaking within the time allowed. All of these are infringements, I will admit I have probably unintentionally done them all at some point, it doesn’t help when you’re surrounded by athletes. In a big pack I wonder how many athletes justify it to themselves because everyone else is doing it around them, or because other’s should drop back first or similar.