Norwegian tri superstar Gustav Iden caused a stir by wearing an adapted pair of the Cloudboom Echo 3s with a reported stack height of 50mm at the 2022 Ironman World Champs.
That's outside of World Athletics’ legal stack height rule of 40mm for road-running events.
At the time those numbers were legal in the more relaxed world of M-Dot tech rules, however, and the Scandinavian duly filled his boots with a 2:36:15 marathon time powering him to the overall victory.
Ironman has since adapted the same rule as World Athletics.
On Cloudboom Echo 3 review
You can instantly see the appeal of the Cloudbooms to elite runners when you step out on the roads.
They’re fairly light at 211g per shoe (UK7), while On’s Cloudtec midsole spec and the full-length carbon plate (as opposed to a shorter plate in the previous Echos) sandwiched between two layers of foam result in plenty of snap and propulsion.
Even though there’s Pebax foam in the midsole, the Echos do produce a firmer ride than many in our recent carbon running shoes test (On also labels them as ‘low cushioning’ shoes), with the 35mm stack height among the lowest among its competition.
The fairly high (in 2023) heel-to-toe drop of 10mm also saw us revert to heel striking, especially late in the run, and personally we wouldn’t go further than a half marathon in these.
They’re also narrower than many of the other carbon shoes we tested, especially in the midfoot, and while they’re nimble enough, some runners will want more support.
Where the Cloudboom Echo 3s really shine is in their upper and outsole.
The perforated former is hugely breathable yet tough wearing, securing the foot tidily with the help of the lithe tongue and proving to be the second best on test for sockless running.
Extra points are awarded for being 100% recycled, too, while transitions were swift even without a heel loop, the tongue sitting neatly in place thanks to a pair of wings that secure it underneath the easily-removable sole.
Like the upper, the outsole also felt the most durable on test, with a rubber compound in the key contact points reducing the chances of wear, and also providing the most confident grip of any On shoe that this tester has previously used (while also possibly adding to the firmer ride).
The lack of exposed lugs also minimises the chances of stones becoming lodged in the outsole.
While we love On’s style, the love isn’t a two-way street. These gave our once-dodgy knees trouble both during and after running, though that’s possibly due to the heel-strike-encouraging 10mm drop, with consecutive run days a definite no.
Yet we know plenty of runners who don’t feel the same way and Gustav Iden, for one, really didn’t seem to mind in Kona last October (albeit in 50mm shoes).
Also worth noting is that men with size 6 (UK feet) can’t experience the Cloudboom experience, with sizes starting at a UK 6.5
Verdict: Expensive and likely to prove divisive, but may find favour for short-course.
Score: 75%
How we tested
These shoes were initially tested as part of a group test of the best carbon plate shoes for running.
They've been reviewed by former 220 Triathlon features editor Matt Baird, who has over 15 years of experience testing running and triathlon kit.
During testing, Matt wore the Cloudboom Echo 3 on a range of runs, including tempo sessions, simulated races and steady runs over a range of distances.
He's rated these shoes based on energy return, propulsion and ride, comfort, durability, stability and suitability to triathlon (e.g. if they're breathable, pull on quickly and can be worn without socks).
