As the part that contains the bearings, your bike's hubs allow your wheels to rotate freely. Without them, you ain't going anywhere.
Hubs function as the center of a wheel and consist of an axle mounted in the frame of the bicycle, a set of bearings around which the wheel rotates, and the hub shell, which allows the spokes to attach the hub.
Whether you are building a new set of wheels or simply looking to replace an old worn out hub, this article will share the information you need to make the right choice.
Choosing a Hub
Hubs have to be matched to the front or rear of your bike; each will be a different size. Rear hubs typically feature a broad mounting platform for the cassette, and each rear hub is made to specifically match a certain class of cassettes.
Hubs are generally 100mm wide in front and 130mm wide in the rear for road bike frames; mountain bikers generally use 135-142mm front and rear hubs to allow space for disc brakes, which require extra material on the outer edge of the hub for mounting the disc.
Make sure your hub matches your frame and fork width as well as your brake type and cassette preference. If in doubt, do some online research or ask your local bike shop. They should be able to help.
Hubs which integrate a freewheeling mechanism into the hub itself are called freehubs, and they allow a wheel to rotate separately from the gearing mechanisms.
On many BMX and fixed-gear bikes, there is no freehub, so the pedals will continue to rotate with the wheels, preventing the rider from coasting but allowing braking by pedaling backwards or locking the pedals in place.
Pricing and Features
Like most bicycle parts, hubs come in a wide variety of prices and with various features. Even the most basic will provide suitable rolling speed and low friction for good performance, but the higher-end models can get a bit confusing. So what, exactly, does your money get for you? Let's answer that question.
Before you start searching for the right hub for your bike, make sure you have the information you need: the type of cassette you will use, the width of the frame and fork, the number of spokes you will be mounting (and the type of spokes that will be used), and whether you will need the ability to mount disc brakes.
Once you have all that squared away, it is time to start looking at features. Basic hubs tend to be constructed out of steel and aluminum alloys and provide good typical performance. They start around $20-$30 in cost, and range up to $90 or so.
High-end hubs for road and mountain bikes tend to be made out of lighter, stronger materials like high-quality aluminum that minimize weight and provide increased strength. They also often use higher-quality steel or ceramic bearings which provide less rolling resistance and a smoother ride. These generally cost in the range of $200-$400 and can push the weight down to around 100 grams -- almost miraculous compared to the 500g hubs of a generation ago.
Some specialty rear hubs provide the ability to measure power output, cadence, speed, distance, ride time and more via a series of built-in sensors. These models are very expensive, sometimes in excess of $1000, and are generally only used by serious racers.
Make sure whichever hubs you purchase are matched to your riding style -- using a road hub on a mountain bike could lead to premature failure.
One last question you may want to ask yourself is whether the hub(s) you have chosen come with an integrated quick-release skewer or solid axle and nut. Some do and some do not, so don't make the mistake of ordering a part without this critical attachment.
Solid axles and nuts provides more theft resistance and are sometimes recommended for use with disc brakes (due to unusual forces that can be applied to the front axle when using disc brakes), while quick-release mechanisms make it easier to change flats and swap wheels on the go.
Also, some mountain bike hubs are designed for wider (diametrically speaking) "thru axles." Check out your suspension fork to see if it uses a standard 9mm skewer or a beefier 15 or 20mm thru axle before you start shopping.
The main issue that arises with hubs is problems with the bearings; over time, the seals that keep water and grit out of the ball bearings can break down, and the wheels can begin to lose some of the smoothness that allows them to rotate freely.
If your hubs have accessible bearings, it is possible to disassemble the mechanism, clean the bearings and housing, and re-seal the hub for further use. This process is beyond the scope of this article; consult other articles or a local bike shop about getting this procedure done.
However, many modern hubs contain self-contained cartridge bearings which are not repairable or cleanable. These confer longer lifespan, higher performance, and tend to be cheaper, but they must be discarded and replaced when they do wear out.
Cartridge bearings are increasingly dominating the market and are used by those seeking the greatest speed and convenience. Many older bikes use the user-serviceable "cup and cone" style bearing.