Whether this was a cause or consequence of the crash remains unclear, but many have already pointed the finger of blame at De Gendt\u2019s wheels, a set of Zipp\u2019s 353 NSW carbon wheels<\/a> with hookless rims<\/a>.<\/p> As a reminder, hookless rims are tubeless-ready rims that lack bead hooks \u2013 the protruding edges on the inside of a rim that help retain a clincher or tubeless tyre bead.<\/p> Thankfully, De Gendt was able to continue racing largely unscathed, however, the incident raises a few questions as to what happened \u2013 and what it may mean for wheel and tyre tech.<\/p> Speaking to Velo<\/a> in the aftermath, Hansen was unequivocal on what had caused the crash, saying \u201chis tyre came off, the safety foam inside got caught in the fork and that locks up the front wheel\u201d.<\/p> The next day, Hansen posted a link to the Velo article on X\/Twitter<\/a>, adding: \u201cThis is true. The @cpacycling is not happy with riders racing on Hookless system in the peloton. There have been concerns from riders and teams with this new system.\u201c<\/p> Dan Bigham<\/a>, a performance engineer at Team Ineos-Grenadiers (and former UCI World Hour Record holder), then retweeted Hansen\u2019s post, adding \u201cHistory will not be kind to road hookless\u201d.<\/p> For his part, De Gendt seemed less sure, posting, \u201cI would like to know what I hit with my front wheel\u201d on X\/Twitter and asking whether anyone had images or footage of the incident.<\/p> Could hookless rims be unsafe for use in professional road racing, or perhaps in cycling altogether, or might there be more to this story than meets the eye? Let\u2019s investigate.<\/p> Though Hansen was definitive about the reason for De Gendt\u2019s crash, it\u2019s not totally clear what caused the incident.<\/p> The grainy video footage available appears to show De Gendt\u2019s front tyre detaching from the rim during the crash, but it\u2019s not clear whether he hit an obstacle or suffered a puncture prior to crashing.<\/p> We do know De Gendt was using 700 x 28c Vittoria Corsa Pro TLR<\/a> tyres on a set of Zipp 353 NSW wheels, with Vittoria Air-Liner tubeless inserts.<\/p> We also know De Gendt\u2019s teammates were using similar, if not identical setups, with Vittoria Corsa Pro TLR tyres on Zipp hookless rims.<\/p> Beyond that, though, there\u2019s much we don\u2019t know.<\/p> We don\u2019t know, for example, whether De Gendt suffered a sudden puncture in the moments leading up to the crash that caused a rapid loss of air pressure.<\/p> The tubeless insert is supposed to help keep a tyre attached to the rim in these scenarios, but it\u2019s possible there was failure with that piece of kit too.<\/p> Likewise, we don\u2019t have details of De Gendt\u2019s tyre pressures. Both Zipp and Vittoria stipulate a maximum tyre pressure of 72.5psi \/ 5 BAR when using hookless rims. Is it possible De Gendt was running tyre pressures over this limit?<\/p> Given his bike would have been assembled by highly experienced professional mechanics, it seems unlikely, but of course, it\u2019s not possible to rule this out (perhaps the gauge on their track pump<\/a> or air compressor is out of spec, for example).<\/p> Could De Gendt\u2019s tyre have been inflated to close to the maximum pressure in the morning (when it may have been cooler) and then been tipped over as the day heated up?<\/p> Potentially; though, while it was clearly warm that day (all of the riders were wearing summer cycling kit), reports from the race don\u2019t mention any kind of extreme heat, so this also seems unlikely.<\/p> Perhaps more likely is De Gendt hit an obstacle, which caused a sudden spike in tyre pressure and a catastrophic blow-off.<\/p> Ultimately, though, we simply don\u2019t yet know exactly what caused this incident. The footage we have isn\u2019t clear enough.<\/p> It\u2019s also possible this was just a freak incident caused by a failure somewhere in the rim, tyre or insert system. None of De Gendt\u2019s teammates suffered similar issues that day, after all.<\/p> One of the key concerns surrounding hookless rims in recent years has been regarding tyre compatibility.<\/p> In situations such as this, it\u2019s natural to ask whether De Gendt could have been using an unsafe or unapproved rim and tyre combination, perhaps in pursuit of improved performance.<\/p> For its part, though, De Gendt\u2019s team, Lotto Dstny, told Cyclingnews<\/a> its rim and tyre combinations are \u201c100 per cent in the rules\u201d, and that it follows all guidelines on this topic from the UCI and its wheel and tyre sponsors, Zipp and Vittoria.<\/p> Indeed, Zipp specifically lists the 700 x 28c Vittoria Corsa Pro TLR as compatible with its 353 NSW rims, on its Hookless Road Tyre Compatibility Guide<\/a>.<\/p> If they haven\u2019t exceeded the maximum permitted tyre pressure, it looks as though De Gendt and his team have done nothing wrong in this instance.<\/p> However, the issue becomes complicated by the latest ETRTO and ISO (International Organization for Standardization) standards for hookless rims. These guidelines state the minimum nominal tyre size for a 25mm internal width rim is now 29mm, not 28mm.<\/p> Hunt, for example, notes it capped the internal width of its latest SUB50 Limitless wheelset<\/a> \u2013 which uses hookless rims \u2013 at 23mm in order to adhere to these updated standards.<\/p> Vittoria says its Corsa Pro TLR tyre is approved for use on hookless rims in a size 28c or larger, but doesn\u2019t offer any guidelines as to internal rim widths on its website.<\/p> Zipp maintains its 25mm-wide rims are fine to use with 28c tyres, per its compatibility guidelines.<\/p> Speaking to Cyclingnews last year<\/a>, Zipp said: \u201cWe know there have been enough wheelsets ridden in the past several years with the 28c tires on 25mm rims to prove that the combination is safe and delivers many proven performance benefits.\u201d<\/p> Clearly, then, there are conflicting opinions on this topic, and an unhelpful amount of grey area.<\/p> After all, how many consumers regularly check the latest ETRTO or ISO standards?<\/p> Perhaps, no one did anything specifically wrong, but this is a case of exceeding the margin for error.<\/p> In response to another user on X\/Twitter<\/a>, who said, \u201cIt\u2019s fine if you use wheels and tyres with the current ETRTO standard\u2026\u201d, Bigham said: \u201cI don\u2019t consider factors of safety as low as 1.1 as ‘fine’.\u201d<\/p> A \u2018factor of safety\u2019 typically describes the strength of a system in relation to its intended use or load, or in other words, its margin for error.<\/p> Though it’s not clear exactly what Bigham is referring to, a safety factor of 1.1 relating to the maximum permitted tyre pressure on a hookless rim would, for example, equate to 79.75psi \/ 5.5 BAR (1.1 x 72.5psi \/ 5 BAR). This gives the rider a margin of error of 7.25psi \/ 0.5 BAR.<\/p> De Gendt\u2019s setup appears to sit in some sort of grey area \u2013 approved by the manufacturer of his wheels and tyres, but potentially not by the ETRTO or ISO.<\/p> Does the crux of this issue lie in the lack of \u2013 or an insufficient \u2013 margin for error, then?<\/p> Again, it\u2019s difficult to say, without further clarification of the incident itself and De Gendt\u2019s specific setup. Perhaps it was on the limit of what\u2019s technically safe and a freak incident pushed things far enough over the limit to cause a failure and resulting crash.<\/p> Would wider margins of error have prevented this incident? Potentially, but without a clear understanding of what caused this incident it feels impossible to say for sure.<\/p> This isn\u2019t the first time we\u2019ve seen issues with tubeless tyres in the professional peloton.<\/p> Last year\u2019s edition of Paris-Roubaix<\/a>, for example, also saw a number of riders suffer tubeless failures with tyres dismounting from rims.<\/p> The thing is, though, bicycle tyres dismounting from rims in professional road racing isn\u2019t anything new.<\/p> Proponents of tubular tyre systems often tout the ability of a tub to stay attached to the rim in the event of a puncture (because the tyre is glued onto the rim), but I\u2019m old enough to remember riders who had tubular tyres roll off their rims after the glue failed during hot races.<\/p> I\u2019m even old enough to remember being too afraid to use tubular tape instead of glue, in case it ever happened to me.<\/p> Likewise, clincher tyres and rims paired with inner tubes \u2013 which some WorldTour teams are still using<\/a> \u2013 also won\u2019t remain securely attached in the event of a puncture.<\/p> So what options do we have?<\/p> Hooked rims alone are clearly not the solution. If riders aren\u2019t using tubeless inserts \u2013 and there\u2019s no UCI rule stipulating they must be used with tubeless tyres \u2013 then a hooked rim won\u2019t help keep a flat tubeless tyre on a rim any better than with a clincher one.<\/p> One of the riders who suffered a tyre blow-off in the Arenberg trench at last year\u2019s Roubaix was a Team Bahrain Victorious rider running Vision Metron wheels, which feature hooked rims, for example.<\/p> Perhaps the best solution is hooked tubeless rims with tubeless tyres and inserts, with two potential failsafes against blow-offs.<\/p> DT Swiss, for example, told BikeRadar it doesn\u2019t produce hookless road rims because it believes hooked rims are safer, especially since it doesn\u2019t make tyres and it can\u2019t control the decisions consumers make.<\/p> Life was certainly simpler before the advent of hookless rims, as the thorny issue of tyre and rim compatibility reared its head.<\/p> However, many here at BikeRadar (myself included) have ridden \u2013 and continue to ride \u2013 hookless rims and tubeless tyres without such issues.<\/p> Indeed, when my colleague Warren Rossiter tested the Zipp 353 NSW wheels in late 2021, he paired them with a set of 28c tyres and suffered no problems.<\/p> Does that prove such equipment is safe? Clearly not. Maybe it is, or maybe Warren was just lucky not to suffer any incidents that pushed the limits of that combination. As I keep saying, it\u2019s difficult to be sure.<\/p> While significant progress has been made on improving compatibility and standards in this area, clearly there are grey areas and uncertainty remains.<\/p> Having a situation where a major wheel manufacturer (Zipp, in this case), and the ETRTO and ISO, provide conflicting information on compatibility to consumers is clearly not ideal either.<\/p> The responsibility ultimately lies with the cycling industry to reach a consensus about what is and isn\u2019t safe, and to communicate that clearly to riders, bike shops and mechanics.<\/p> I\u2019ve written about this topic at length in the past \u2013 in my long-term review of a Giant TCR Advanced Pro 2 Disc<\/a>, for example \u2013 and as I\u2019ve commented before, the benefits of hookless rims may be obvious to manufacturers, but the benefits for riders are far less so.<\/p>Hansen speaks out<\/h2>
![\"Dan](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2024\/02\/Dan-Bigham_Hookless-tweet_2024-02-25.jpg\")
What we know \u2013 and what we don\u2019t<\/h2>
![\"Thomas](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2024\/02\/GettyImages-2032374088_EDIT-scaled.jpg\")
![\"Vittoria](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2023\/07\/Vittoria-Corsa-Pro-TLR-01-2e6e805.jpg\")
Was De Gendt using an unsafe rim and tyre combination?<\/h2>
![\"Thomas](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2024\/02\/GettyImages-2032377340_EDIT-scaled.jpg\")
![\"Extract](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2024\/02\/Zipp_Vittoria_Hookless-tyre-compatibility_2024-02-27.jpg\")
![\"Continental](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2023\/06\/20230525SvBEOS-RO5A9379-55c840c.jpg\")
Margin for error<\/h2>
![\"Dan](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2024\/02\/Dan-Bigham_Hookless-tweet_Factor-of-safety_2024-02-25.jpg\")
![\"Road](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2021\/06\/Road-bike-tyre-pressure-9-d745d1b.jpg\")
Have we been here before?<\/h2>
![\"A](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2019\/03\/1403195441426-1flcl4wu0pca8-1466679458907-7a54oiu1qqy2-b6fd8fa-e1594379731921.jpg\")
![\"Bikes](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2024\/02\/GettyImages-1481009759_CROP-scaled.jpg\")
Where do we go from here?<\/h2>
![\"Movistar](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/39\/2023\/06\/20230525SvBEOS-RO5A9370-8ab3d33.jpg\")