The wheels connect the bike to the road.
The Hubs are the heart of a wheel. They have bearings that allow the rotation of the wheel. The only difference between a front hub and a rear hub is that the rear hub has mechanisms for mounting a gear or gears. Most bikes have a freewheel body to allow the rider to coast but some do not like track bikes. Most freewheel bikes can accommodate more than one gear. Some have as few as three to as much as 11. These allow the rider to find the optimal gear for their level of effort.
With the hubs, there are Skewers to facilitate the firm connection to the frame. Most have a quick release mechanism for easy placement and removal of the wheels. The quick release works by pressing the frame/fork unto the wheels. Some disc brake-equipped bikes use a through-axle (or thru-axle) technology. This means that the skewer goes into one side of the frame/fork, through the hub of the wheel and then screws unto the other side of the frame/fork.
An example of a hub with quick release mechanism.
Example of a thru-axle on a disc brake bike.
The Rim of the wheel is attached to the hubs via Spokes. Common rim materials are aluminum alloy and carbon fiber. Most entry-level rims are made from aluminum alloys and the competition-level rims are made from carbon fiber. Aluminum rims are heavier than carbon fiber rims but they are more durable. Carbon fiber rims are lighter and helps the rider accelerate faster. Because carbon fiber rims are lighter, they can be made into "deep" wheels or rims with high/tall profiles. This allows for better aerodynamic performance compared to rims with lower/"shallower" profiles.
Different wheels need a different number of spokes. Normally used spoke materials are steel and carbon fiber. Some wheels have as much as 36 spokes while a select and expensive spokes have as few as 12 spokes. Several high end wheels do not need spokes such as disc wheels and tri-spoke wheels (and other similar designs) as these are made from pure carbon fiber.
Tires are the main contact points of the wheels - and the bike - to the road. Tires are the exterior and the tubes are the interior. Wider tires are more supple and more comfortable than narrower ones. Just be sure to purchase an appropriate tube for your tire of choice and that your frame can accommodate the tire you want. To fill up the tires with air, Tubes are normally used. These tubes fit between the tires and the rim. Tires the use tubes are called Clincher tires. Clincher tires have an edge to latch onto the hook of clincher rims. This goes for majority of bikes. However, there are tire designs that do not need tubes such as Tubeless and Tubular tires. Tubeless tires require a fluid sealant within the rim and the tire to seal it and fill it with air. Tubeless rims have hooks similar to clinchers. On the other hand, tubular tires have a built in tube. Tubular rims have a smooth concave surface and require the tubular tires to be glued onto them. Tubulars are normally used by pro road racers.
For braking, wheels can be designed for rim brakes, disc brakes or both. Wheels for rim brakes have a braking surface on the rims where the brake pads will apply pressure. Braking surfaces can be aluminum or carbon. Wheels for disc brakes have discs/"rotors" attached on the hubs. These are where the brake pads will apply press on to stop. It is possible for a wheel to be designed for both. The rim has a braking surface and the hub can accommodate a rotor for disc braking.
A rim with a carbon braking surface.
This concludes our article on bike wheels. I hope you learned a lot in this article. Remember the names of the different parts and I hope this helps you when maintaining or maybe looking for your next wheels and tires.
Please stay tuned for Part 4 - Drivetrain.
Here is a link to Part 1.
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