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Certain Supershoes Deemed “Illegal” Under New Rules

If you were hoping to race in Gustav Iden's Kona-winning Ons or the new 55mm Adidas Adizero Prime X this year, we've got bad news for you.

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Ironman has followed the lead of the sport’s governing body World Triathlon and banned ‘supershoes’ with soles thicker than 40mm or that contain more than one carbon plate. The move comes as part of the brand’s updated 2023 competition rules and means a material change (in every sense) for pros and age-groupers alike.

As first reported by Triathlete, Gustav Iden wasn’t breaking any existing regulations when he ran a 2:36:15 marathon to win the Ironman World Championship title in Hawaii last October. Iden was wearing a pair of On prototypes loosely based on the Cloudboom Echo 3, but with a midsole thicker than 40mm.

Iden “got away with it” because World Triathlon, whose technical rules Ironman generally adopts, had chosen not to follow a 2020 World Athletics ruling outlawing thicker soles and multiple carbon plates. The position was addressed at a World Triathlon executive board meeting in Abu Dhabi last November, which stated that World Athletics rules would be followed starting January 1, 2023. Ironman has now aligned too, with its updated policy stating:

  • Shoes with a stack height sole thickness of greater than 40mm are prohibited and will result in disqualification.
  • Shoes containing more than one plate rigid structure are prohibited and will result in disqualification.

While Iden is perhaps the most high-profile athlete who will need to switch footwear, he is far from the only triathlete the ruling affects. For example, the winners of the inaugural Ironman Israel Middle East Championship in December, Patrick Lange and Ruth Astle, both ran in the Adidas Adizero Prime X, with a 55mm stack. While not banned at the time, this shoe is now outlawed under Ironman’s new rules—although it is widely available on public sale.

The other issue addressed in the updated policy is wearing prototypes or customized shoes that are not on mass sale. The principle of the ruling is to try to allow all athletes to benefit from the same level of equipment choice. Here Ironman states the shoe either has to be on World Athletics’ pre-approved list of running shoes or a request must be submitted to the World Triathlon Technical Committee for it to be approved as a development shoe.

In practice, pro and age-group athletes can be subject to random shoe control before, during, or after any race and any shoe that cannot be identified may be sent to the World Triathlon headquarters for verification. Breaching any of these rules will result in disqualification.

RELATED: What Makes Supershoes Super?

Gustav Iden (L) in the now-outlawed supershoes at the 2022 Ironman World Championship race. (Photo: Tom Pennington/Getty Images)

The prototype problem

It’s good to see Ironman aligning with World Triathlon after the sport was found dragging its heels last summer. The new regulations make sense, but the proof will be in how well they are implemented. This is true not just for Ironman, but other race series who follow World Triathlon technical rules, including Challenge Family, Clash, and even local races sanctioned by a national federation (like USA Triathlon).

While stack height is more easily governed, customized and prototype equipment – not just with running shoes – has long been used in triathlon, and often in a gray area of legality. Bespoke chest fairings used by some pros in Kona last year are one example of this – banned in the world governing body of cycling (Union Cycliste Internationale, or UCI) but only addressed by World Triathlon rules in the context of draft-legal and paratriathlon racing. Gray areas and confusion over the rules can cause issues with enforcement as well (see also: Daniela Ryf’s illegal wetsuit at Ironman and PTO events).

Don’t expect run times to become dramatically slower with this new rule, however. Shoe brands are already pushing right to the limit of what’s possible within the World Athletics rules. The popular Asics Metaspeed – as worn by Kristian Blummenfelt – comes in at a 39mm sole thickness, and it’s doubtful Iden will be losing much sleep over wearing a slightly-less-chunky pair of Ons.

Our prediction: Expect shoe tech to keep on improving, and run performances to become ever-more eye-watering.

RELATED: Supershoe Showdown: The Best (Legal) Racers, Head-to-Head