Nobody actually has to follow ETRTO. At least not in the U. S. They are (voluntary) standards, not regulations. ZIPP still approves 28s on the 25 ID rims. Whether you trust them or not is another matter. I personally ride 30s (32.6 actual measurement) on my 303 Firecrests. Would have preferred if they were hooked, but at my tire size and pressures, I am not particularly concerned.
Exactly, but this is part of the problem. It also gets complicated. You have to trust the wheel maker, the tire maker, and then both in combination. But thereās no independent way to make sure it works. (A lot of things are like that tho, itās not unique to hookless)
The other problem is that tires are not standardized. A tire labeled 28 will vary significantly between brands and models. In this case, we have to trust manufacturers on their claimed compatibility.
My issue is that manufacturers have not provided a convincing response that their recommended specifications are safe. I understand that some of their testing protocols are IP but Iām hoping a better answer than ātrust us we do extensive testingā.
The other things Iād like to know is whatās the production variance in tire width, how much it changes during a ride due to changes in temperature, atmospheric pressure, etc. I donāt know the technical terms but in simple words. How much wiggle room?
Iām in a similar boat. I use 30 and 32mm tires on 23 IW rims with psi in the 50s. Probably on the safe side but Iām starting to worry about some incidents. For example, blowing out the tire by hitting a pothole in a way that wouldnāt be enough to flat but because the additional pressure created by the impact.
I know something like that can still happen with hooked wheels but itās extremely rare.
I give this example because long time ago after an edition of Roubaix I remember someone from one of the big bike brands said something like the chances of the tire coming off just by increasead pressure due to an impact were very low because you need X amount of force to increase pressure by Y amount and they tested at Z psi. If an impact is enough to increase pressure above Z psi, that will damage the wheel and burst the tire anyway. The conclusion was that the tires of a rider came off as a result of a flat or wheel damage first, itās unlikely that the tire just came off. This was with hooked wheels. I probably butchered the explanation but I hope I conveyed the idea.
I donāt think any of the manufactures have provided a convincing argument that incidents that are usually safe on hooked wheels will also be safe on hookless. Not only in a perfect scenario.
wowā¦that was fantastic
This is exactly the point.
There are too many if or thats to make sure a tire rim combo is safe.
And mostly everyone here is more bike savvy then the average joe. How the hell do you expect the average joe to select a safe combo?
They wonāt. They will just buy a tire and rim combo like they used to do. But now they are unaware they are riding on a potential fatal combination.
Hambini has just released a video on hookless rims, they seem a bit suspect to me (and I have a set). Why make a wheel and tyre combo less safe? Obviously itās good for the wheel makers as it improves their bottom line, until the lawsuits start coming inā¦
I wouldnāt worry about those combinations in the slightest.
For my Zipp rims, there are a handful of tires that are a very known quantity. I feel pretty comfortable with Continental. They are widely used and explicitly approved by the rim manufacturer. I have hit stuff VERY hard, to the point that my teeth rattled and I wasnāt sure I would stay on the bike. No burping or anything. But of course, anyone can produce an out of spec tire. I am mindful when mounting for sure. I like my tires finger cramp tight.
If it helps, this is the same as my winter/trainer bike setup - Zipp 303S with 23mm IW, 30mm tyres (that blow up to ~32mm), psi in the 50s. Iāve done >15,000 miles on that setup including 3 UK winters on some pretty terrible roads with absolutely no issues. Have even managed to hit a big pothole so badly that I cracked the rim (group ride in the rain, rider in front of me wasnāt paying enough attention, saw it late and decided to bunny hop it instead of pointing it out 
) and although I lost all the pressure as the sealant sprayed out through the crack the tyre still stayed on even in that scenario. I feel confident riding that setup and would happily recommend it to anybody with a similar use case i.e. looking to run wider tyres with lower pressures for all round riding.
I wouldnāt recommend hookless for high performance road racing or TTing right now - I still run hooked wheels on my race bike, as from the data Iāve seen/heard there is still an aero penalty for going wider than about 28mm (and very few if any wheels are aero optimised around anything wider than 28mm), and as an 80kg rider on a 28mm tyre hookless pressure limit of 73psi starts to become an issue. Especially as some of my races are on nice smooth tarmac where optimal pressure for rolling resistance is higher. I think a 28mm tyre on a 25mm IW rim for a heavier WorldTour rider (De Gendt is listed as 73kg) on the super smooth (and hot) roads of UAE is simply a bad choice. Would think that a Zipp 454 with 23mm internal width would have been a better option if he wanted to run 28mm, but then that only has 28mm external width (the 353 is 30mm) so maybe an aero penalty from not following the rule of 105?
Do also wonder whether the liner and/or pressure they were using is also a factor though as other teams seem to be running hookless with no problems - UAE are on Enve and Iām not aware of any reported problems there. It is still astonishing how little knowledge or understanding of hookless there is even among shops and mechanics I speak to.
For the engineers hereā¦is the fix for this a different tire construction?
Sounds like hookless is safe at 32c
I wouldnāt be at all surprised if most pros inflated their tyres to higher pressures than recommended to increase rolling resistance performance at the expense of comfort.
From what I can ascertain you only bag the lower rolling resistance benefit from bigger tyres if you over-inflate them - otherwise you are taking an aero and weight hit for nothing.
Yes and noā¦higher isnt exactly better..though it certainly can be on a perfect surface. A better way to look at it is thereās a sweet spot for any given surface - too low psi is slower, too high a psi is also slower.
And itās pretty well known that 5psi higher than optimum is usually slower then 5psi lower than optimum, so best to err on the low side.
Iāve also heard this only applies to hard surfaces. Once youāre on dirt, as low as you can go without rim striking is generally faster.
Where is this information from - sounds interesting?
I was just taking rolling resistance - not considering suspension losses or anything like that.
Most pros were running lower pressure I thought, or innos is it sounds like
Tadej was running 30mm Saturday
You need to take both into account. If you look at smooth steel drum testing, higher pressures are always better. But when you take suspension/impedance losses into account that occur, they get much worse at higher pressure.
See this silca blog for some road testing where they found a 9w penalty for being 10psi higher than optimum, but only a 1 watt penalty from being 10 psi below optimum for brand new asphalt. On rough, freshly ground roads, they didnāt test low enough to find the optimum.
https://silca.cc/blogs/silca/part-4b-rolling-resistance-and-impedance
Second chart shows it well - increasing pressure gradually decreases Crr right up until impedance losses āoverwhelm the systemā, at which point Crr rises sharply. Given that most of us are dealing with less than perfect roads and have neither the time nor expertise to determine where that deflection point is, itās better to be a bit low than a bit high.
WorldTour teams do have data guys who can analyse this stuff and optimise it much better, and the roads in UAE in particular are super smooth so the optimal pressure for those roads may well exceed 73psi.
Ah, you beat me to it!
Itās probably also worth noting that wider tires have lower CRR AT THE SAME pressure.
Source
The big question is whatās the fastest combination. Presumably youāll ride a 28mm tire at a lower pressure than a 23mm tire, offsetting some of that difference. The 23mm tire is also likely more aerodynamic (assuming the wheel tire combination is optimized). Where is best combination of aerodynamics, CRR, and interaction drag w/ the frame/fork/rider.
The answer is most like, it depends.
Of course, a wider tire at lower pressure is going to be cushier to ride.
Yeah this is the point I was originally trying to makeā¦ gives the pro teams a reason to overinflate a wider tyre for rolling resistance gains.
Also from the charts it looks like the losses from overinflating a tyre for imperfect surfaces happen at pressures a fair bit higher than what would be safe on hookless - again potentially giving teams a window where best performance is at a pressure above what is safe.
I did notice that the chart was based on 25mm tyres however - would be interesting to see where the sweet-spot for 28-30mm tyres is - suppose it could put the sweet spot at a āsafeā pressure for hookless - but wouldnāt be surprised if it didnāt.