One wheel collapse that was not the fault of hookless rims or incorrectly inflated tyres

When this image and others from Omloop Nieuwsblad appeared on social media and online over the weekend, fans and commentators were quick to speculate as to what had happened, with some keen to blame hookless rims, tubeless tyres or carbon wheel construction.

The real cause however wasn't so scandalous.

The image clearly shows the Cadex rear wheel of Amaury Capiot's Giant Propel completely destroyed with the hub separated from the spokes, the tyre having come off the rim which is cracked (just below the race number), and white sealant sprayed liberally over the rim and frame.

It's the kind of image manufacturers dread, as it results in wild speculation in the age of hookless rims and tubeless set-ups. And not without reason. At this year's UAE Tour Fabio Jackobsen was the latest rider to crash after hitting a rock in the road resulted in his tyre and tyre liner coming off the front wheel.

This was two years on from Thomas de Gendt suffering a similar fate, which prompted the UCI to announced it was reviewing hookless rims 'as a matter of urgency' in March 2024.

Since road bikes moved to disc brake set ups, rim design has exploded (no pun intended) with rims and tyres getting ever wider, tubeless - or tubeless ready tyres - becoming the norm and hooked and hookless rims being developed by different manufacturers with ultra-tight tolerances. The lack of standards across the industry has resulted in an increase in potential for miss-matched tyres and rims. Throw in a drastic drop in ideal tyre pressures and you have a more opportunity for outcomes like this one.

CyclingNews reported Jayco AlUla saying the wheel failure was a result of "riding too long on the cobbles with a flat tyre". They went on to say that due to the time it can take a team car to get to a rider who's experienced a flat, that Capiot opted to "go for as long as he could, which ultimately caused the wheel to fail".

So why did we see the spokes separate from the hub, and the rim retain it's shape?

Carbon spokes and reinforced rims transfer more load into the hub and flanges, which likely explains why we saw hub flanges or spokes failing at the centre of the wheel in this case.

The enormous amount of energy transferred into the hyper-rigid system, without the tyre to manage it, is transferred in and out of the rim, into the spokes, then hub. That energy has to come out somewhere. Add pedalling force in a wheel that's already damaged, and your wheel is not going to last long.

Regardless, the truth remains, that whilst some wheels can and no doubt have survived this kind of incident, no wheel, hookless, hooked, carbon or even alloy is meant to survive being ridden directly on cobbles without a tyre.

Without a tyre, cobblestones likely send some 30-50 times more force into the wheel than it was designed to withstand. So when tens of thousands of newtons strike a rim in milliseconds, failure is just physics.

Opinion - Why you should never ride on a flat

Andy Carr

Founder of Spoon Customs that designed and built some of the world's most coveted custom bikes, Andy has also been an Alpine ride guide, thus spending most of his life on two wheels

Now, I’m not a hookless fan. And the hooks clearly have a role in retaining the tyre in some circumstances, but my lengthy investigations last year, concluded that whilst the system works perfectly well when set-up correctly – and I have never experienced a problem with it myself – there’s a fairly narrow window in which it’s safe.

And for me, and almost every industry insider I asked, the Hookless window is decidedly tight. Especially for a system joe public is asked to set up and manage themselves, in a huge variety of variable settings.

A modern road tyre is not cosmetic. It is the bicycle’s primary suspension system. As chassis expert Tony Foale explains, in his many excellent books on the subject, a pneumatic tyre stretches the impact over time, reducing vertical wheel velocity, and spreading force around the rim.

Remove it, and the wheel system itself is incomplete, and the rim, spokes and hub is then forced to absorb the full blow of an impact almost instantaneously.

With a 30mm tyre in place, a sharp 25mm cobble hit at race speed transmits forces in the range of 3-6kN, the tyre physically deforms to absorb it and spreads the load around the rim. Modern wheels are designed to handle that. Not always without flatting of course, but they’re designed to handle it.

Remove the air from the tyre, or lose it completely and keep riding – as appears to have happened here – and that same impact can spike toward 150-250kN – a huge order higher. At that point, even a single stone (let alone a course made of cobbles) becomes a death sentence for what’s left of the wheel.