Hookless Rims Explained

What are hookless rims? How do they differ, and what are their pros and cons compared to the “ordinary” clincher rims (the ones with hooks)?

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Table Of Contents (T.O.C.):

1. What are hookless rims?
2. Hookless rim pros and cons
3. When are hookless rims a good idea?

1. What are hookless rims?

Before answering this question, let us briefly consider the “standard” clincher (or “hooked”) rims. A hook on a rim helps keep the tyre from blowing off when inflated to high pressure, or when it faces sideway forces (like when a wheel starts sliding sideways, and then suddenly regains traction).

Now, let’s compare clinchers to a hookless rim (the picture is taken from my article about bicycle rim tapes):

Hooks on a rim provide a good anchor for a tyre, thus enabling the use of lighter tyres with more flexible sidewalls. Such tyres would too easily slide off a hookless rim – and thanks to their supple sidewalls they provide a lower rolling resistance. That’s one of the main reasons why people started making rims with hooks some fifty years ago (in the ’70s of the XX century). Pretty quickly, “hooked” (clincher) rims became a standard, replacing practically all the hookless rims.

Today, hookless rims are becoming “fashionable” again. Why? Read on.

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2. Hookless rim pros and cons

Hookless rims have the following advantages compared to hooked rims of the same weight and width:

• They’re stronger.
• They let the tyre sit a bit wider on the rim – as there are no hooks pushing the tyre further inwards relative to the rim’s sidewalls. More volume for the same tyre width (and mass) gives a bit softer ride and a bit lower rolling resistance, with a potential for a slight aerodynamic bonus.
• Easier and cheaper to manufacture (especially when it comes to carbon fibre rims).

These advantages are relatively small and hardly measurable. Clincher rims too can be quite light and strong, with a tyre that is seated nicely. The main advantage of hookless rims is for the manufacturers – faster and cheaper production.

Downsides are the same as they used to be fifty years ago: hookless rims require heavier tyres with stiffer sidewalls to prevent them from being blown off the rim at higher pressure or sideway loads. This describes tubeless tyres perfectly: they need beefier and a bit stiffer sidewalls to hold air without a tube, and to prevent them from getting pushed away from the rim and losing pressure upon impacts. Let’s now briefly recapitulate the hookless rim cons:

• Limited tyre choice (boils down to, generally heavier, tubeless tyres).
• Maximum pressure of about 5 bars (70 PSI) – generally.

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3. When are hookless rims a good idea?

Briefly: hookless rims make sense for wide tubeless tyres.

Tyres that aren’t tubeless will not work nicely with modern hookless rims!

Before I continue, a brief overview of tubeless tyres:

The main advantage of tubeless bicycle tyres is they can be ridden at very low pressures without getting snakebite flats upon impacts. Low pressure, along with more width, helps on rough or muddy (or snowy) terrain. Also, tubeless tyres can self-seal smaller punctures, thanks to the sealant liquid that is poured inside of them. Their main disadvantage is they are a hassle to mount (because of their stronger and stiffer sidewalls) and regularly change the sealant fluid.

For more details, see the article: Tubeless bicycle tyres – pros and cons explained.

Narrow road bike tubeless tyres require higher pressure, so they don’t use the biggest pro: the low-pressure “operation” (also, self-sealing works worse at higher pressures), while not avoiding any of the tubeless tyre cons.

To be more specific, I’ll quote my reply to Ryan:
For the purposes of this article, for average rider+bike+luggage weights, I would say that narrow tyres are below 37 mm (or below 1.5 inches). Though, on a light road bike, ridden on paved roads, one could consider a 32 mm tyre to be a low-pressure, wide tyre.
It boils down to what the optimal pressure for the riding conditions and the whole system weight is (optimal tyre pressure article).
If your optimal tyre pressure is over 4 bars, I would avoid hookless rims (or tubeless tyres for that matter).

Do you now understand why I think hookless rims are a bad idea for road bikes – or any other bikes without wide tubeless tyres?

What about the wide (MTB) tyres? If you think tubeless tyres are a good idea (considering their pros and cons), it makes sense to pair them with hookless rims.

Let me wrap this up with a quote:

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 – from BikeForums

If you have any questions (or additions and corrections), please use the BikeGremlin forum:
www.bikegremlin.net

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