The axles, hubs, and quick releases of the wheels are bicycle components that do not receive as much attention as others. However, they are very important in terms of the bike’s handling and feel, as well as its maintenance. Together, these three parts are responsible for ensuring the attachment and integration of the wheel with the bike frame, as well as the stability and stiffness of the wheel in motion. In this general guide, we introduce you to their features, measurements, and the most commonly used standards in the market depending on the preferred use or type of the model they are mounted on. We also give you some maintenance tips to avoid play and breakdowns.
Wheel axles: function, types and maintenance
The axle of your bicycle wheel is the fundamental piece connecting the first and second, and it supports much of the force and loads exerted on the wheel. That is why it must be stiff and strong. The axle is a component that has changed little in past decades, but in the last ten years has seen the emergence of many different sizes and dimensions, making it impossible today to speak of a single standard. Nevertheless, three main types of bicycle wheel axles can be distinguished, which can be found in all disciplines (mountain biking, road cycling, and gravel cycling).
Traditional QR axle
This was the most widely used type of axle before the arrival of thru-axles and Boost. Both the fork and the rear dropouts of the frame have open slots underneath where this 9 mm diameter axle is housed, with springs and end caps to ensure proper attachment, closure, and easy removal. The front axle is 100 mm wide and the rear is 135 mm. Both have a QR quick-release lever that allowed the wheel to be quickly removed or reinstalled on the bike. In recent years, it has lost presence on wheel and bike builds, now being seen only on lower-end models and on city or hybrid bikes.
15 and 12 mm thru-axle
These were the first thru-axles to appear at the beginning of the last decade, coinciding with the popularization of disc brakes. The diameter increases to 15 mm and 12 mm for the front and rear wheels, respectively, while maintaining the same width of 100 mm and 135 mm in their first generations, later increasing to 142 mm for the rear. They also change their shape and removal method. Instead of being threaded on both sides and coming with springs, it is a solid bolt that passes through one side, goes through the hub, and threads into the other side. This makes wheel removal easier and provides more stiffness and stability to the wheel assembly and, consequently, to the entire bicycle.
Boost axles
They became popular on mountain bikes
A few years ago, as a way to add extra stiffness to both axles and modify the chain line to design larger wheel clearances to accommodate wider tires without sacrificing weight, the front axle adopted the 15x110 mm standard and the rear one 12x148 mm. This is the type of axle that has become standard on most mountain bikes today and on quite a few road bikes
and gravel
. In addition to these three reference axle types, in more radical mountain biking disciplines such as enduro
or downhill
, wider axles are usually installed to give the bike greater stability and poise when tackling technical descents. These are thru-axles with widths of 120 mm at the front and 150 mm or 157 mm at the rear.
Axle maintenance
At least once a month, it is advisable to remove the axle and the wheel and thoroughly clean both the slots or threads of the fork (depending on whether a traditional or thru-axle is used) and all axle parts, and apply a little assembly grease to the ends, or over the entire surface if they are thru-axles. This will make it easier to quickly remove or install the wheel on the bike and will prevent the appearance of creaks or play.
The hub: materials, types, and maintenance
The hub is a fundamental part of the wheel. It surrounds the axle, connects to the ends of the spokes, houses the brake disc, and serves as the support for the cassette in the case of the rear, being responsible for transmitting the movement from the drivetrain to the wheel so it can spin.
In addition, it provides stiffness and stability to both wheels and is crucial for bike control when climbing, descending, or turning. The star material for bicycle hubs is aluminum. Although their internal parts, nuts, pawls, etc., are usually made of steel, as are the bearings inside. There are also carbon fiber or titanium hubs, but these are much more exclusive and reserved for high-end wheels or bike builds.
It is advisable to clean and grease the inside of the hubs at least once a year
As for measurements, they have the same axle widths mentioned above. In the case of the rear hub, they house an extension to install the cassette, called the cassette body. Boost hubs end up being wider and thicker than standard thru-axle or 9 mm QR hubs, thus providing more stiffness and poise to the wheel but also more weight. Regarding maintenance, it is advisable to disassemble each one, both front and rear, and give them a thorough cleaning (including the bearings) at least once a year. In the following Globeros BTT video, they explain step by step how to properly maintain them. This preventive operation will prevent play and avoid more costly breakdowns.
Wheel closures: which one is best for my bike?
Finally, we need to talk about the different types of wheel closures, which are used to mount and remove the wheel and to ensure it is properly attached to the bike frame or fork. The most commonly used type of closure for decades has been the Quick Release, and it is the most recommended if you do mountain biking occasionally and are not very skilled at mounting and removing wheels. It is a small lever that is used to tighten or loosen the axle fixing bolt on the bike, depending on whether or not we want to remove the wheel. However, in recent years, and with the aim of preventing the lever from breaking due to excessive tightening force or from falls or impacts, nut closures that open with a specific Allen key, such as the SRAM Maxle Stealth, have become popular. This is also the system used on the new Cannondale with Lefty or single-arm forks. In this way, you avoid the quick release lever being damaged or breaking and blocking the removal of the wheel, with the extra benefit of reducing some grams (30 per axle) from your bike. On the other hand, you will have to carry with you at all times an Allen key suitable for the size of the nut. It is a more specific type of axle, limited to mid- and high-end bicycles.