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Hookless Rims

Old 09-28-22, 09:27 AM
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Hookless Rims

Confused about hookless rims. I am looking around for carbon rims (for a fatbike, ideally to take 45NRTH Dillinger 5s). Nearly everything I am able to find is hookless. I thought I understood the concept, but then I started seeing rims described as "Clincher / Hookless". Even though I've read several pages describing the difference between hooked and hookless rims, I'm still confused about what tires I can expect to function correctly with hookless rims.

The 45NRTH Dillinger 5 is described as having a bead that is "Tubeless Ready Folding". Are hookless rims supposed to work with that?
The Origin8 Supercell is described as a clincher tire with a wire bead. Are hookless rims supposed to work with that?
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Old 09-28-22, 01:21 PM
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Not the answer but an observation.

It is somewhat funny that a feature that when introduced was thought of as being such a big improvement (hook beaded rims, allowing far higher tire pressures) is now considered no longer needed because we have basically gone back to tire widths and pressures that were the norm 60+ years ago on performance bikes. This industry is truly cyclic and suffering from short term memory

From what I have read and been told one of the major motivators for hookless rims is because the molding of the hooked edge with a layered material construction (carbon tow/cloth in plies), the compression needed for the strength and the shape/dimensional control required makes for a very complex mold with what is called "negative draft" (the overhang of the hook edge WRT the rim's inner side wall. Eliminating that hook edge opens up the rim interior and reduces the mold's cost and complexity by a lot. Now it only leaves convincing the public that tires that are less securely held on the rims (or so hard to mount or remove that on the road repairs are vastly harder to do) is a good thing. Entering from the left is the marketing department... Andy
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Old 09-28-22, 02:07 PM
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First of all, let's understand that what holds the modern tires to rims is the wire (or fiber) bead which is strong enough to resist expansion under load. The rest is geometry. The rim has to be designed so that that wire can be maneuvered over the rim's larger OD, then positioned in such a way that it cannot repeat that on it's own. The key is a deeper central well that allows the tire to move inward at one section & thus outward at another.

There are basic methods for accomplishing this.

1- rims with a shoulder having a diameter matching the tire's ID, and using pressure to hold the tire outward so it cannot slip down into the well. This is the design of so-called straight side rims, and has been relied on in everything from hand trucks, to bicycles, cars, trucks, and giant earthmovers, and so on. It's a proven design that will hold a tire on regardless of pressure provided that the tire's bead is strong enough. (until the rim fails).

2- rims with a hook edge near the OD and outside of the tire's bead. The corresponding tire has a recess above the bead, so when mounted and inflated the tire is pressed outward, and the bead is trapped below the hooked edge. This "modern" design that Mavic introduced to narrow high pressure rims some time back is actually quite old, and most of us started our bicycling careers using rims and tires of this design on our 20" bikes.

So there's no need to worry about straight side rims and tires doing the job. The simple fact that both designs, while different in their approach, are functionally equal as long as they're executed well.

FWIW - the term "clincher" as applied to modern tires is a misnomer. BITD (actually well before BITD) there was a different design that didn't require a wire bead at all. The tire and rim interlocked together in such a way that added air only made the "clinch" tighter. Some modern hook edge tires borrow from this old design and save weight by using the constraint offered by being trapped under the hook to use less strong beads. Obviously this can create some incompatibility, but unfortunately little clarification is offered at sale, so the margin for user error is significant.
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Old 09-29-22, 12:17 AM
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Originally Posted by FBinNY View Post
First of all, let's understand that what holds the modern tires to rims is the wire (or fiber) bead which is strong enough to resist expansion under load. The rest is geometry. The rim has to be designed so that that wire can be maneuvered over the rim's larger OD, then positioned in such a way that it cannot repeat that on it's own. The key is a deeper central well that allows the tire to move inward at one section & thus outward at another.
I would disagree. I can mount a tyre using my hands - so the bead is not preventing it from slipping off under pressure.
It's the air pressure pushing the tyre sidewalls against the rim sides that holds the tyre in place.

Bead is just used to prevent it from slipping off until the pressure is high enough to hold the tyre in place.
However, past a certain point, it's the pressure pushing against the rim sides that holds the tyres in place.

Hooks allow the tyres to withold a higher pressure before being pushed off the rim, as it traps the bead section beneath the rim's hook using the same air pressure that also tries to push the tyre off the rim.
(for this, bead's expansion resistance is irrelevant)

But saying that wire (or fiber) bead holds the tyres to rims is like saying that the kick-start keeps the motorcycle running.
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Old 09-29-22, 07:49 AM
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I disagree with BG. Having seen many tires that have the wire of the tire's bead no longer contained by the casing, the casing fibers being cut or abraded, and seen the tire side lift off the rim side wall too many times to think that wire is unneeded.

Then there's the cases when the tire bear is not seated in the rim, it is slightly above the rim, but the tire hasn't lifted enough to allow the tube to herniate out. That wire is what is holding the tire from completely lifting off. Andy
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Old 09-29-22, 05:49 PM
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Alright, so I guess I haven't been thinking correctly about the purpose of the bead. I have always understood it as a protrusion that engages the hook, seating underneath it. It's probably true that it does that, however the bead really serves a more important role: it is the inelastic part of the tire that won't stretch to a larger diameter. As long as the bead stays centered, which it would do when it is seated, then the tire can't slip off. The worst it could do is "burp" a little.

So any tire that has a bead should function with hookless rims. I think I get it now. Thanks!
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Old 09-29-22, 06:37 PM
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From what I've been told from the people who sell carbon, hookless rims to bike shops, they are a way to make it more viable, for lack of a better word, for carbon rim makers to make a rim. I think what I'm saying reflects what Andrew R Stewart said in post #2. We have yet to sell or stock any of these rims in my shop, nor do I have any personal experience with them, so all I know about them is based on hearsay.
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