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If you are buying a new wheelset, you might encounter two hub flange designs: closed and open. Open hub flange designs have a troubling history, as they can lead to complete loss of spoke retention, potentially causing a sudden, catastrophic wheel collapse in a crash or hard impact.
In this article, I’ll explain how both systems work, where open flanges make sense (especially with carbon spokes), and when you’re better off choosing a safer, closed or “captured” design.
KEY TAKEAWAY
Open hub flanges are common on wheels with carbon spokes and can offer weight and manufacturing advantages. However, they rely heavily on spoke tension and, without a proper capture system, may not retain spokes well in extreme situations.
Closed flanges (or open designs with an effective spoke-capture solution) add a bit of weight but provide better structural integrity and keep spokes in place even after damage. For most riders, they are the safer and more robust choice. That’s one reason why many manufacturers, especially Chinese brands, are moving away from fully open flanges toward closed or semi-captured designs.
What Hub Flanges Do
Hub flanges are the parts of the hub to which the spokes attach. They transfer load between the hub and the rim and significantly affect wheel strength and stability.
Closed or enclosed flanges, without large cutouts, are usually heavier. In exchange, they offer better structural integrity and reduce stress concentrations around the spoke interface.
Because the flange supports the spoke head or threaded end, its design also affects long-term durability and the wheel’s behavior after spoke damage or failure.
Open (Cutout) Flange Hubs
Open, or cutout, flanges have windows or slots that expose the spoke heads or ends instead of fully enclosing them.
On some designs, especially older steel-spoke systems, an open flange combined with simple J-bend or large-head spokes can allow a spoke to be ejected if tension is suddenly lost, such as after a crash.
In open flange hubs, if several spokes fail and opposing tension disappears, the remaining spokes can rotate or “spin out” of the hub shell. There is no mechanical stop to keep them in place. This can lead to complete loss of spoke retention and a rapid wheel collapse.
Wheels with open or cutout flanges that lack any capture system rely primarily on spoke tension and flange geometry to keep spokes seated. In rare but severe events, hard pothole impacts, bike-to-bike contact, or crashes, multiple spokes can detach at once.
This failure mode is uncommon in everyday riding, but it does occur. It has led to recalls and design changes in the past, particularly on high-end aero wheels.
Open Flanges and Carbon Spokes
Modern carbon road wheels are where open flange issues are most relevant. Carbon spokes are usually wide, making them impossible to insert through small, fully closed holes.
The downside is that many of these designs lack true mechanical capture if tension is lost. This problem primarily affects carbon-spoke wheels. Steel-spoke hub manufacturers learned long ago that fully open flanges without retention are problematic and largely abandoned them.
On open-flange carbon hubs, losing a few spokes in a crash can cause the remaining spokes to sequentially eject from the hub as the wheel deforms and rotates.
Open Flange Solutions that Might Work
Nepest uses a patented open-flange hub design on its NOVA wheels that aims to address some of the traditional weaknesses of open flanges. Instead of relying purely on spoke tension, Nepest’s system shapes the flange windows and spoke interfaces so the spoke heads are partially captured within the hub shell. Although the flange is visually open, the spokes sit deeper and are guided by the flange geometry, helping to prevent them from freely ejecting when tension drops.
This approach keeps the weight and assembly advantages of an open flange, while improving spoke retention compared to fully open, window-only designs.
However, it remains fundamentally an open flange system. In extreme crash scenarios, it cannot provide the same level of mechanical security as a fully closed or threaded capture design. It’s best viewed as a safer evolution of the open-flange concept rather than a full replacement for closed flanges.
TIP: Based on my discussion with Patrick Clark, co-founder of the wheel brand Particle, who has deep insider knowledge of Chinese wheel factories, it is wise to be somewhat skeptical of patent and aerodynamic claims or impact test results, especially when they come from Chinese brands.
Closed (Enclosed) Flange Designs
Closed-flange designs fully enclose the spoke head or threaded end. Even if spoke tension drops, the spoke cannot fall out. In some modern systems, spokes even screw into the hub flange using a threaded insert. The threads act as a positive capture mechanism, keeping the spoke seated even when it is cut or it loses tension.
However, this system can be prone to spoke twisting, loss of tension, and deviation from the most aerodynamic orientation.
Closed flanges are typically heavier because they use more material. However, they distribute the load more evenly and avoid the sharp stress points common in open-flange designs (see the image below).
In the following demonstration, wheel builder and Caden Wheels founder Ben Cawood cuts two carbon spokes on a front wheel and then rides uphill out of the saddle at around 95 kg body weight. Despite the missing spokes, the remaining spokes stay in the hub and the wheel remains rideable.
This demonstrates the key safety advantage of closed or captured flange systems: the wheel can deform and lose local tension without immediately ejecting spokes from the hub.
Conclusion
Open flanges with carbon spokes were originally popular because they simplified lacing and spoke replacement. They were also lighter and looked more attractive on specification sheets.
However, several well-known Chinese brands, including Winspace (Lún) and Elitewheels, have moved away from the open-flange designs they used in their early generations. Complete wheel failures are rare, but I believe this shift is positive.
When it comes to wheels, I’ll happily accept a few extra grams in exchange for better spoke retention and a lower risk of catastrophic failure. I’m also glad that the manufacturers listened to feedback from reviewers like Peak Torque and adjusted their designs accordingly.
I also updated my past wheel reviews to include this information. I clearly identify the type of flanges each wheelset uses so you can make a more informed decision.
If you are in the market for a new wheelset, I recommend checking out my in-depth guide on how to choose road bike wheels.
