Many high profile wheel brands, including Zipp, Enve and Cadex have switched from marketing carbon wheels with hooked rims to hookless rim designs. They cite aerodynamic advantages, as well as lower weight and less waste during manufacturing as key reasons for the switch.
But what are hookless rims, why has the design recently become popular for road bike wheels and why would you choose them over hooked rims?
Here, we’ll explain what hooked and hookless rims are and delve into the pros and cons of choosing a hookless wheelset, helping you to decide which rim design is right for you.
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What is a hooked wheel rim?
Until recently, wheel rims for road bicycles would invariably have a bead hook to the rim. The hooks are the small thickened parts at the very edge of the wheel rim, which are there to help with tyre retention.
They hold the tyre bead in place, so that the tyre shouldn’t separate from the rim however high the pressure or rough the ground over which you’re riding.
What is a hookless wheel rim?
A hookless rim has straight sides, without a hook to the rim. In the industry, it’s often called TSS for ‘tubeless straight side’, a term that you might see used in discussions of hookless rims.
Hookless rims have been a feature of many mountain bike wheels for a number of years, but they’re a fairly recent development for road and gravel bike wheels and mostly confined to premium wheelsets. With beefier tyres run at lower pressures, the wheel-to-tyre interface is more substantial in mountain bike wheels than those on road or gravel bikes.
Why are hookless rims becoming more popular for road and gravel bike wheels?
The advent of tubeless tyre technology for road and gravel bike wheels and the increasing use of wider tyres has resulted in tyres being run at significantly lower pressure than a few years ago.
While 23mm tyres with tubes were often inflated to over 100psi, it’s now more typical to run 28mm or wider tyres tubeless at 70psi or less on road bikes. Along with closer tolerances for the manufacture of both tyres and rims, this has made a bead hook less important for tyre retention.
What are the advantages of a hookless rim?
The advantages of hookless rims come to the fore once you plan to ride with tubeless tyres; in fact they’re usually designed to be run exclusively with tubeless tyres. The wider contact area between the tyre and rim helps to provide a robust, airtight seal.
Without a bead hook, it’s possible to make the wheel lighter and stronger. It can also be more aerodynamic, as the interface between the tyre and the rim is smoother than with a hooked rim, where the tyre shape is more like a lightbulb.
The flatter sides should also reduce the risk of pinch flats, allowing the tyre to be run at lower pressure, which potentially provides a smoother, faster ride.
There are advantages for the wheel maker too, although these are largely confined to carbon wheels. Laying up carbon fibre for a hooked rim is more complex than for a hookless rim. This results in a greater reject rate from manufacturing and more waste, which of course is also reflected in the retail price of wheelsets with hooked rims versus hookless rims.
Zipp’s switch to hookless was accompanied by a price decrease for many of its wheels, for example.
And what are the disadvantages?
A major disadvantage is tyre compatibility. For the tyre to seat safely on a hookless rim, it needs to have closer tolerances in its circumference than when there are hooks to help keep it in place.
Wheel and tyre makers have worked together to ensure that tubeless tyre and hookless rim combinations are compatible. This has included testing to pressures significantly greater than those recommended for day-to-day use.
The ETRTO/ISO guidelines for testing require tyres to be inflated to 1.5 times the recommended operating pressure to ensure that they won’t blow off a hookless rim. Wheels with hookless rims will be tested against this standard, while a wheel maker may exceed it in its testing.
Not all tyres pass the test and some wheel brands publish listings of recommended tyres that can be used with their hookless rims. Sometimes, hookless compatibility is dependent not just on the tyre model but also its width, with tyres narrower than 28mm sometimes not marked as compatible with a brand’s wheels, while those of 28mm or more are compatible.
For safe operation, it’s also important to keep below the recommended maximum tyre pressure. With the trend to run wider tyres on road bikes at lower pressures, this may not be such an issue, but it’s important not to exceed the 73psi / 5 bar maximum pressure recommended by ETRTO.
Likewise, there’s a lower pressure below which there’s an increased risk of a tyre dismounting without hooks to help hold it in place, or ‘burping’ and losing air, so hookless rims may not be suitable for cyclocross and some gravel uses. There may be more risk of a tyre dismounting if run flat too.
Which type of rim should I choose for my next wheelset?
Whether to choose hooked or hookless rims is largely a matter of which wheel brand you are considering (and how much you want to spend).
Zipp, Enve, Giant and Cadex carbon rims are hookless; DT Swiss says that it plans to retain hooked rims on its road bike wheels, as it considers this to be safer. Campagnolo’s latest Bora and Bora Ultra wheels also have hooked rims, while the latest Hunt Sub50 Limitless Aero wheels are hookless, replacing the previous generation 48 Limitless which had hooked rims.
For the majority of riders, if they want to run tubeless, there should be no downside to choosing hookless rims, beyond the tyre compatibility, width and pressure considerations discussed above.
Heavier riders might want to remain with hooked rims to allow them to run at optimum tyre pressure though. If you live somewhere hot, there's a slight pressure increase when you take your bike outdoors from your air conditioned garage. It's likely to be around 2.5psi between 25C and 35C.
If you’re not sure you’re committed to tubeless tyres (which require more regular maintenance than tubed tyres), you might want to choose hooked rims. Cheaper wheels, particularly those with alloy rims, are likely to continue to use hooked beads.
Hooked rim wheelset examples
Mavic Cosmic Ultimate 45 Disc
Mavic’s latest premium Cosmic Ultimate 45 Disc wheelset has a claimed 1,255g weight, carbon spokes and a hooked bead design.
'“'We don’t believe that all customers are ready to be limited by 75psi or only use 28mm tyres, so we haven’t gone hookless or super-wide with the wheels’ internal width,'”' says Mavic’s head of product management, Maxime Brunard.
- Buy now from Condor Cycles (£3,499.99)
DT Swiss CRC 1400 Spline CX
DT’s cyclocross-specific CRC 1400 Spline CX wheelset has gone from a hookless rim design in its previous generation back to providing a hooked bead in the current iteration.
DT says that this is to ensure wide tyre compatibility with cyclocross tyres and also, as mentioned above, to help lower the risk of burping and losing air at the low pressures typically used in cyclocross races.
- Buy now from Tweeks Cycles (from £662.99)
Hookless rim wheelset examples
Zipp 858 NSW
Zipp’s flagship 858 NSW wheelset, as with its other wheels has a hookless bead as well as Zipp’s distinctive waved profile and a 23mm internal width. It’s aero optimised for 28mm tubeless tyres. In our review, we noted the low weight of 1,563g for such a deep rim, which included tape and valves.
- Buy now from Tredz (from £1,585)
Hunt Sub50 Limitless Aero Disc
Hunt’s latest premium aero wheelset, as we discussed above, has a hookless design in place of its predecessor 48 Limitless’ hooked rim. Alongside a swap to carbon spokes and a new, lighter hub, Hunt says that the change to hookless has helped it reduce the weight of the Sub50 Limitless Aero wheelset to 1,380g from the 48 Limitless’s 1,618g.
- Buy now from Hunt (from £1,479)
Taking the plunge to go tubeless? Read our guide to the best tubeless repair kits.
