trail wrote:
imswimmer328 wrote:
A hookless rim allows the manufacturer to use metal tooling in the rim bed, which produces a higher quality laminate. It will be stronger in terms of hoop stress, potentially more impact resistant, that's going to be material system and geometry dependent. However, the bicycle industry is unlikely to be using the most modern toughened resins, and as such the reality of carbon fiber is that any impact of the sort will destroy the rim like this. I do wonder if the culprit is lower pressures causing a rim strike that wouldn't have happened in previous times. I do recall last spring the escape collective nerd alert team attributed the tires coming off at Roubaix to broken wheels, seems we may be seeing more of that in recent times.
Also you could "spend" the improved laminate property to make a lighter wheel instead of a strong one.
On the second point, seems valid. Anecdotally back when I was using latex tubes I found the likelihood of a pinch flat started to explode around 80PSI. That's why I converted 100% to tubeless. A pinch flat is essentially a rim strike, so it would stand to reason that we'd be getting more rim strikes at the more common <80PSI pressures.
Certainly in the MTB world an enduro or DH rim is built quite a bit stronger than an XC rim (or certainly a road rim) specifically because of rim strike likelihood - particularly at sub-30PSI presssures. One of the reasons that hookless is effectively ubiquitous in MTB at this point.
i don't know if it's necessary for me to mention this, but i don't think breaking a rim in this fashion is a function of hookless 5 bar limits. i think it's more likely because the ideal pressure for this wheel during, say, strade bianchi is much lower. maybe 45 to 55psi depending on the tire. whether hooked or hookless i don't know that a lot of folks realize how hard the ride would be if you ran 5 bar in a 28mm tire on a 25mm internal width rim. i've ridden parts of the strade bianchi's typical route and that would be a terribly high pressure to ride on the gravel roads that i was on. it's not that 72psi isnt high enough to prevent a rim strike; it's that 45 or 50psi might be the ideal pressure and the downside is the possibility of a rim strike.
Dan Empfield
aka Slowman