I finally ran into a conundrum with hookless wheels and gravel bikes. I have Zipp 303 firecrest wheels and was perusing the tire compatibility on the SRAM website and immediately realized that the max tire width for the wheel is 50mm. I trust that the Escapees here are much more rational and smarter than I am, so please explain to me the ways in which I would threaten my physical well-being by running 53mm tires on said wheelset. I am deathly afraid of dental bills (US resident here), so I’m initially quite apprehensive of pushing manufacturer recommended guidelines anyway.
I’d be more concerned with running a too narrow tire than too wide personally. The former would require too high a pressure. If the rim is rated for 50s it’s hard to imagine 53s would be dangerous.
But max pressure varies inversely with width/tire volume, no?
Honestly not sure, but I have 303 Firecrests and have been running various Schwalbe Pro tires (RX,RS) 50s and they are fantastic. Maybe if you are worried you could try those in 50s. I run them from maybe 23 psi to 30 per conditions.
I think Zipp is really telling us the limits of hookless. I used to run 40c tires on 17mm internal width rims and cantilever brakes without issue, and historically I think rims have underestimated their max width. It does add to the side load forces on the tire/rim connection though, and personally I think Zipp has been trying to hide too many of the shortcomings with hookless. This might another one and I could see a real risk of increase tire roll off.
That’s an interesting position by SRAM. As far as I can tell, the ETRTO guidance and pretty much every other wheel and tyre brand says 53mm tyres would be absolutely fine on a 25mm internal rim, hookless or otherwise (hookless is pretty standard for MTB wheels anyway).
I’m generally reluctant to ignore manufacture advice, but in this instance, and given you’re only talking a couple of mm, you’re probably fine.
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Don’t take my word as definitive, but I’d say that:
- The pressure you try to run the tyres at is the most important thing, so you don’t risk the tyre blowing off.
- They might be basing recommendations on more than just pure safety, but how they experienced ride feel and/or performance.
- Too wide a tyre is probably not a safety concern as such (at least not from tyre blow off standpoint, if you account for the max pressure being lower), but it could be that over 50mm the way the tyre reacts when cornering could be a problem (I.e., the rim starts to roll over on the tyre).
- could it be that without the hook, the tyre bead isn’t held at the right angle/is more likely to roll, when a tyre is over a certain size, making point 3 worse/happen at a narrower tyre width compared to hooked rim?
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Yes but I think rims have a max pressure as well.
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