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What is a "hooked rim"?

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What is a "hooked rim"?

Old 06-26-12, 08:57 AM
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What is a "hooked rim"?

Was swapping out my tires last night and after mounting the front, read all the text on the sidewall to determine inflation recommendations. Under one of the paste-on logos was some raised rubber type that was difficult to read. Had to get a magnifying glass to figure out what it says. It says, (paraphrased), "Mount Only on a Hooked Rim". What is a hooked rim?

Tires are Bontrager Race X Lite 700x25 and the wheelset is a Dura-Ace WH-7850-C24-CL
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Old 06-26-12, 09:03 AM
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Your rims are "hooked", it just means they have a bulbed rim edge to help keep the fully inflated tire stay mounted and not blow off like a non-hooked rim can do. Some older rims are non hooked.
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Old 06-26-12, 09:06 AM
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Modern rims generally come in one of two types. The classic straight side rim locates or seats the tire on a shoulder matched in diameter to the inside of the tire and has flat (insides) to keep the rim from blowing off. The only thing that keeps the tire on is the strength of the wire bead which resists stretching enough to go over the top and blowing off.

Hook edge rims have ridge or hook along the inside of the outer edge. The tires bead goes below the hook which seats the tire. Hook edge rims are better for high pressure light tires, especially those with Kevlar vs. steel beads. The tire's own pressure keeps the tire from blowing off by pushing the bead under the hook and trapping it there. This design reduces the strength requirement for the bead and allows higher pressure, lighter tires.

There are those who say that tire pressures of 90psi and more are only possible with hook edge rims, but that's not exactly true. Before hook edge rims came into fashion, various companies made high pressure steel bead tires designed around the straight side rim. But most HP tires today are designed around the hook edge rim, and have inadequate bead strengths to work properly with older straight side rims.
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Old 06-26-12, 09:14 AM
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Thanks guys. I suspected that is what they are and I wanted to make sure before I hit the road and possibly loose a tire at speed. That would not be pretty.
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