Dear Lennard,
Your road tubeless Technical Q&A is excellent in the way only LZ can deliver excellence - critical, timely, polite, thorough, technical, un-emotional. What about Tadej Pogačar’s crash in the 2024 Giro d'Italia? Here is the video of the crash (at incredibly slow speed including white sealant explosion) that could have killed him under his own team car. And the Lotto Dstny crashes?
Morgan
Dear Morgan,
Thanks for pointing out that Drege’s crash was by no means the only one in pro races related to a sealant-spewing tubeless tire. Fortunately, the UCI is on it! The organization that is so good at listening to the concerns of riders that it fined Julien Bernard 200 Swiss francs for stopping to kiss his wife and son during the stage 7 time trial of the recent Tour de France is going to get to the bottom of this hookless rim/tubeless tire matter.
As you mentioned, the Lotto Dstny team has had a pair of tires, along with their tire inserts, come off their rims in big races this spring, bringing their riders down along with them. Thomas De Gendt’s crash in the February UAE Tour presaged the crash by Johannes Adamietz in Strade Bianche in March. In both cases, their Vittoria tires and green tubeless inserts had jumped off their Zipp front wheels and were left dangling off their Orbea forks; one bead of De Gendt’s tire remained on the rim (see photo), while Adamietz’s tire came completely off.
According to Zipp, both riders hit obstacles so hard that they broke their hookless wheels, allowing the tires to come off. This zoom-in on his wheel does show that it’s cracked. De Gendt wants to know what he hit, as it’s not visible in the video of his crash.
Anybody who has broken a rim with a tubeless tire on it knows that it will indeed come right off. But does that excuse guaranteeing that the rider crashes? I was riding this Zipp 303 wheel a few years ago when I hit a curb obscured in shadow full on at nearly 30mph. I managed to lift the front wheel enough that I only slightly cracked it, but the rear wheel slammed into the curb full force. Thing is, my tires had inner tubes inside. Both tires stayed on, and I stayed upright. With tubeless tires, the rear one would have undoubtedly come off instantly, and I very likely would have crashed. Ouch. With his tubeless setup, even with the tubeless insert inside, De Gendt never stood a chance of not slamming into the road, and his wheel was certainly not broken worse than my 303 was.
Both Lotto Dstny riders were on Zipp 353 NSW Tubeless Straight Sidewall (TSS, aka “hookless”) rims with 25mm internal width. Their 28mm Vittoria Corsa Pro hookless-compatible, tubeless-ready tires set up tubeless with Vittoria Air-Liner hexagonal-cross-section foam tubeless inserts. Lotto-Dstny mechanics seem to get the gravity of the situation, saying “We've done it from day one, with a former brand also; we always use inserts. I certainly believe you get a loss of 1.0 or 1.1 Watts, but we do it for the security of the riders.If you have a hookless rim and a tubeless tyre and you get an instant flat it goes off like nothing. Imagine if a rider takes a descent and the tyre goes off… they could be dead.”
But is that really adequate security, given that a tubed clincher and certainly a tubular would not go “off like nothing” from the rim? And then you have the question of rims whose inner width is wider than the ISO recommendation for a 28mm tire that I brought up last week in relation to Drege’s death.
Adam Hansen, the UCI CPA riders’ union president has been quoted saying: “The CPA are 100 percent against hookless rims. Tires should not come off a rim. The maximum PSI these hookless tires can have put in them is 73, and if you hit something for sure it goes above the maximum 73 PSI rating on impact. That is why the tires are coming off.” He goes on to explain, as I did here last week, that the rims are lighter and less expensive to build and hence favored by the wheel brands.
I don’t know what caused Pogačar’s flat tire in the Giro. Clearly, he was concerned about it coming off the rim and went very slowly around the corner. That still wasn’t enough—it came off anyway, the tire and rim being so well lubricated by the sealant. My understanding is that he was following instructions from the team car to go around the turn before receiving service. Big mistake. You cannot turn on a flat tubeless road tire. Period. That is not the case with a tubular, and usually not with a tubed clincher, either.
― Lennard
Dear Lennard,
You may have already written about team Visma’s disastrously crashy spring season. Any thoughts on their tire setup? And given that Matteo J’s rear tire just let him down in the TT.
Lauren
Dear Lauren,
Visma-Lease a Bike rides Cervélo’s in-house Reserve wheel brand which are “semi-hooked”and the same Vittoria Corsa Pro 28mm tubeless tires as Lotto-Dstny.
I don’t think the crashes by Wout Van Aert and Jonas Vingegaard in the spring had anything to do with tire choice. Van Aert crashed into a bunch of riders who had already come down at high speed in front of him in the Dwars door Vlaanderen. Vingegaard was in the wrong place (or the wrong race!) at the wrong time on a sketchy descent with roots lifting the asphalt on a turn in the Itzulia Basque Country race that took him and a whole lot of other riders (including Remco Evenepoel and Primož Roglič) off the road. The crash in the Critérium du Dauphiné that sent Dylan van Baarle and Steven Kruijswijk to the hospital was caused by a super-slippery section of wet road that took down a lot of the peloton (also including Evenepoel and Roglič), not a tubeless tire failure.
I saw Jorgensen’s crash in the final TT, but I didn’t see that he had a tire problem…
― Lennard
As a frame builder, Lennard Zinn has been designing and building custom bicycles for over 42 years; he founded Zinn Cycles in 1982. His Tech Q&A column on Substack follows his 35-year stint as a technical writer for VeloNews (from 1987 through 2022). He is a former U.S. National Cycling Team member and author of many bicycle books including Zinn and the Art of Mountain Bike Maintenance, Zinn and the Art of Road Bike Maintenance, and The Haywire Heart. He holds a bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to: veloqna@comcast.net.
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