Bike hubs are an essential component of a bike, allowing your wheels to spin smoothly and, on the back wheel, dictating the time it takes for your wheel to engage - that is to say, how long you have to pedal for before you start to move.

If you need any advice or help regarding bike hubs, book an appointment at one of our workshops and our experienced mechanics will be happy to help.

What do wheel hubs do?

Just as bikes have front and rear wheels, they too have front- and rear-specific wheel hubs. The front hub is simply designed to enable the wheel to spin smoothly, while the rear hub is a little more complicated as it also forms part of the bike’s transmission – the mechanism which drives the rear wheel and is attached to the rear hub, which on most bikes also features a system which will allows you to coast, with the exception of single speed “fixie” bikes and track bikes.

What’s in a bike hub?

A hub consists of a hub shell, which serves to protect the internal components of the hub;

• Axle, around which the wheels spin
• Bearings, which enable your wheels to rotate freely
• A freehub driver body, which is found on the back wheel and transmits your power to the bike via the cogs/cassette mounted to it - it is also responsible for the ability to coast on bikes, and is the part which makes that beautiful clicking noise
• End caps, which secure the hub
• Disc rotor mount, which is either a splined mount for centrelock disc rotors or a 6-bolt mount system used in 6-bolt disc rotors.

Wheel hub mechanism

The rear wheel hub is what enables the wheel to spin freely when you are coasting, but to engage the transmission when you turn the pedals. This is on the whole because of a toothed drive/ratchet ring inside the hub body and pawls/ratchets in the freehub body. When you are freewheeling, the pawls inside the freehub click past the teeth, creating the famous bike clicking noise, but when you start pedalling, they engage, catching on the teeth and transferring your pedal power to the wheel.

The number of teeth/pawls is a consideration for some riders when upgrading their rear hubs as while bigger teeth can deal with more torque, more teeth mean better engagement rate and more immediate power transfer, which is useful for mountain bikers who need to frequently stop and start or ratchet their bike (take a half-stroke to avoid hitting something).

Which hub is right for you?

A replacement or upgraded hub can give your bike a performance advantage with reduced weight and higher-quality bearings available in many aftermarket units. However, the type of hub you choose will depend on many factors including bike type, axle dimensions, riding type and budget.

It is important to know that the hub you should get will depend on your type of riding. As such, there are specialised mountain bike and road bike hubs.

Choosing your bike wheel hub

Aside from the obvious decision – front or rear – there are several things to take into account when choosing a new hub or hub set, among them bearing type, materials, disc mount standard, axle type and rims.

Bearing type

Good-quality bearings, sealed and protected from dirt and water, are the key to long-lasting and healthy hubs. Older or less expensive hubs may use cup and cone bearings, which contain two rings of loose ball bearings that sit in ‘cups’ inside the hub body and are secured in place by conical nuts known as ‘cones’. The balls can rotate freely between the cup and cone with each unit making up one bearing.

Cup and cone bearings have the advantage of being easily serviced at home – new bearings and a dollop of grease occasionally are all you need to keep them running smoothly – but they can be tricky to adjust perfectly. More expensive hubs may use cartridge bearings, where the steel balls or needles rotate in a single cartridge unit that can be easily removed for servicing or replaced once worn out. Many riders prefer the convenience of cartridge bearings – no more tedious micro-adjusting or hunting for stray ball bearings mid-service – but they are more expensive to replace.

Bike hub materials

Most hubs, front and rear, will be made of lightweight aluminium alloy although carbon fibre units are available at the top end of the market. Some rear hubs, generally those on MTBs, may use steel rather than aluminium freewheels to prevent the hub being chewed up under heavy load.

Brake rotor compatibility

Bikes running disc brake systems need wheel hubs to which the disc rotor can attach. There are two main standards for rotor mounting, six-bolt and Centrelock. As the name suggests, six-bolt systems have hubs with six evenly spaced holes to bolt onto a matching rotor. Rotor bolts generally use Torx heads so you will need to make sure you have a Torx tool to tighten or loosen them - an Allen key will strip the bolts.

The Centrelock system used by Shimano and SRAM foregoes rotor bolts in favour of a splined hub-rotor interface secured with a locking ring (special tool needed). This is claimed to reduce installation time, but it does put limits on mixing and matching hubs and brakes as most other manufacturers stick with the six-bolt system. However, adaptors are available to mount six-bolt rotors to Centrelock hubs, and vice-versa. Before investing in new hubs check which disc interface you are currently using and buy accordingly.

Axle size

You must also ensure that your wheel hubs are compatible with your fork axle. Many entry-level or shorter-travel cross-country forks attach to the hubs via quick-release (QR) skewers, with a 9mm diameter axle clamped into the fork and frame dropouts via a 5mm QR skewer. However recent years have seen the growth of the ‘bolt-through’ or ‘thru-axle’ standard. These axles have a larger diameter (12mm, 15mm or 20mm) for extra stiffness and security, with the axle threading right through the fork ends and being secured by two QR clamps integrated into the fork lowers.

If you intend to upgrade or change your hubs, make sure your new hubs match whichever axle standard you are using.

Rims

If choosing a new hub to rebuild a wheelset you will need to match the number and type of spoke holes on the hub’s flange to those drilled into the rim. For example, a 32-hole hub is designed for a 32-spoke wheel and needs to be matched to a 32-hole rim.

You'll be able to find premium wheel hubs to enhance your ride from leading bike brands such as Chris King, Vel, Zipp and DT Swiss at Sigma Sports as well as a huge selection of other components for road, gravel and mountain bikes.

Bike Wheel Hub FAQs

Are all bike hubs the same size?

No, but there are some industry standards. The most common hub spacing standard for road bikes is 100/130mm (front/rear hub widths) for quick releases, while disc equipped road and gravel bikes are going wider with 100/142mm widths and 12mm diameter through axles. Meanwhile mountain bikes using 100/142mm width hubs with a 15mm diameter thru-axle are more common. You’ll also see ‘Boost’ axle widths coming in at 110/148mm widths and 15mm/20mm axles – found on burlier Trail/DH MTBs. However, there are still some other hub spacings, so always check your bike before buying a new hub.

How can I tell if my bike wheel hub is bad?

If your wheels feel rough as you spin them, that likely means that it’s time to replace your hub. Usually, the issue is due to the bearings in the hub degrading.

Is upgrading my bike hub worth it?

A new bike wheel hub is a worthy investment and can completely change the feel of your bike. Regardless of whether you’re seeking quick engagement or high torque, a new wheel hub can elevate your cycling.

If you have any other questions or doubts regarding your bike hubs, talk to an expert, such as the ones at our Hampton Wick and Oakham stores.