Bike components explained: a jargon buster to all of the key frame, wheelset and groupset parts on a bicycle

Get your head around headsets, drivetrains, derailleurs and more

A graphic showing key bike components

If you’re new to cycling, there is tons of bike-specific terminology to understand if you want to get to grips with how your machine works and what each bike component does. Some are pretty obvious and self-explanatory, whereas other bike parts are a bit more tricky.

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Bike components such as bottom brackets and freehubs have a lot of complexity hidden away – and bike brands seem to love to come up with new and slightly different ways of doing things. Even pedals come in a confusing number of variants.

Confused? Here’s your jargon buster on all the key bike components – and an explanation of what they do.

Want more information? We’ve got full explainers covering the key parts of a bike, so hit the links to get the lowdown on the seemingly infinite number of standards and compatibility questions.

Frame

Let’s start with the frame itself – the heart of any bike.

Bikes have been made from a variety of different frame materials over the years.  Today, they’re most commonly made of either aluminium alloy or carbon fibre, although steel, titanium and magnesium alloy are also options.

Bike frames are typically a double-diamond design, with a front triangle composed of the seat tube, down tube, top tube and head tube, and a rear triangle composed of the seat tube, chainstays and seatstays. We’ll come on to each of these parts of a frame.

Full-suspension mountain bikes have a floating linkage between the front and rear triangles, with a rear-suspension system to allow controlled movement between the two.

Hardtail mountain bikes rely on a suspension fork for their bounce, combined with a rigid rear end.

Bike frame tube names explained

Down tube

The down tube runs from the head tube to the bottom bracket.
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The down tube is the part of the bike frame that slopes down from the head tube at the front of the bike to the bottom bracket, which houses the crankset. It’s the backbone of the bike’s strength.

Top tube

The top tube runs from the head tube to the seat tube.
Simon Bromley / Immediate Media

As its name suggests, the top tube runs along the top of the bike frame’s front triangle, from the top of the head tube to the top of the seat tube. Originally horizontal, it’s now more common for it to have a slope from front to back, particularly on mountain bikes.

On road bikes, the slope results in a frame designated as ‘compact’ or ‘semi-compact’, depending how much of a slope there is.

Seat tube

The seat tube runs from the top tube to the bottom bracket.
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The seat tube runs from the bottom bracket up to the seatpost, at the rear of the bike’s front triangle. It may be straight or have a kink in it and some have a cut-out section at the rear to fit around the back wheel, allowing the chainstays to be kept shorter.

Head tube

The head tube runs from the headset bearings at the top to the fork at the bottom.

The head tube is the short tube at the font of the frame, which supports the headset bearings that keep the fork in place.

Seatstays

The seatstays connect the seat tube to the chainstays.

The two seatstays connect to the seat tube at one end and the chainstays at the other, to support the rear wheel. They’re typically skinny, to help add comfort at the rear of the bike. If a bike has rim brakes, there’s often a bridge between the two seatstays to support the rear brake caliper.

Chainstays

Chainstays run between the bottom bracket and seatstays.
Simon Bromley / Immediate Media

The two chainstays run from the frame’s bottom bracket to the rear of the bike, where they meet up with the seatstays and support the rear wheel. On the driveside, the chainstay also supports the rear-derailleur mechanism.

Fork

Your bike’s fork consists of (usually) two legs to support your front wheel and a steerer tube that passes through the bike frame’s head tube and turns on bearings to enable you to steer.

Road bike forks are typically made of carbon fibre, but may have an alloy steerer tube, although you can also find all-alloy or steel forks, usually on cheaper bikes.

Most road cyclists will use the fork that comes with their bike or frameset, without giving it a second fork. However, tyre clearance and mounting points – for mudguards or luggage – are things to consider when it comes to the versatility of your bike.

Mountain bike forks are more complex and typically include suspension.

There are differences in how this works and how it’s damped, how the fork is attached to the frame, and also the amount of suspension travel (i.e. movement) it offers.

The amount of suspension travel will provide a guide as to the bike’s intended use, with cross-country mountain bikes offering less travel than downhill mountain bikes, due to the tamer terrain encountered.

Frameset

Frameset is used to describe the frame and fork as one package.
Matthew Loveridge / Immediate Media

Frameset is used to describe the frame and fork together.

If you’re building your own bike, you will, in many cases, buy a frameset from a manufacturer, but frames and forks are also available separately.


Wheelset

The wheelset comprises both front and rear wheels.
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Your wheelset is the pair of wheels on which your bike rolls; both the front and the back wheels.

The wheelset comprises all the bits that go to make up the wheel: hubs, spokes and rims, with the freehub that enables you to freewheel on your bike.

The wheelset doesn’t include everything else that you need to attach to your wheels to make them useful, though: tyres (although some brands such as Mavic sell their wheels complete with tyres), inner tubes, cassette and disc brake rotors.

In the case of quick-release wheels, the wheelset includes the axle and usually the quick-release skewer that attaches it to the bike. With thru-axle wheels, the axles are considered part of the bike. If you buy a thru-axle wheelset, it won’t come with them.

Bike wheel parts explained

Rims

Bicycle rims are typically made from aluminium or, in this case, carbon fibre.
Alex Evans

The rim is the circular part that gives the wheel its circumference.

The rim holds the tyre in place and will be designed for use with clincher tyres (with an inner tube), tubeless tyres or tubular tyres.

Hookless rims are increasingly common on wheelsets made specifically for tubeless tyres.

Rims are typically either made from aluminium or, on more expensive wheels, carbon fibre.

Wheels for use on bikes with rim brakes – typically cheap road bikes or hybrid bikes – will have a braking track incorporated into the rim.

The rims are connected to the hub by spokes, which in turn are attached to the rims by spoke nipples.

Spokes

The spokes run from the hub to the rim.
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The spokes attach the hub to a wheel’s rim.

The number of spokes used varies between wheelsets and is often different between the front and rear wheels.

Spokes are usually made of steel, although some high-end wheels use carbon spokes to save weight. It’s common for spokes to be ‘butted’, where they’re narrower in their middle section than at their ends.

Most spokes are either straight-pull, with a hub-end flange that’s in line with the spoke blade, or J-bend, where there’s a 90-degree curve at the hub end, and the design has to match how your hubs are drilled.

They’re screwed into the rim with nipples, which may be aluminium alloy or brass.

Spokes are usually made from steel.
Warren Rossiter / Immediate Media

Hub

The hub sits at the centre of a wheel.
Simon von Bromley

The hub sits at the centre of a wheel, with a shell that turns on an axle, and bearings between the two to lower the friction. The hub shell will include flanges that hold the spokes, and which then lace the hub to the wheel’s rim.

If you’ve got a disc brake bike, the hub shell will also include an attachment point for the brake rotor. This can either be six bolt holes around its circumference or a serrated Centerlock ring, both on its left-hand side.

On its right-hand side, the rear hub on a modern bicycle wheel usually has a freehub, which includes a mechanism to let you freewheel, and to which you attach a cassette.

The hubs on the front and rear wheels combined are sometimes referred to as a hubset.

Freehub

The freehub protrudes from the right-hand side of the rear wheel.

It supports the gearing cassette, which you use to transmit your pedal power to the bike. The freehub contains a ratchet or pawl mechanism that allows you to freewheel.

Our guide to freehub standards covers everything you need to know.

Axles

Bikes with disc brakes are more likely to also incorporate thru-axles (middle/bottom above) instead of traditional quick-release skewers (top).
James Huang / Immediate Media

There are two main forms of what people frequently recognise as wheel ‘axles’, which hold the wheels in the frame: the quick-release and the thru-axle.

Quick releases were invented by Tullio Campagnolo. They consist of a central skewer with a cam lever at one end and an adjusting nut at the other to hold them in place in the frame drop-outs, and are commonly used on rim-brake bikes.

Thru-axles are now nearly ubiquitous on disc-brake bikes. They tighten into circular apertures in the frame, with one end being threaded so that you can tighten the bolt in the frame. Thru-axles give more precise positioning between the frame and the wheel than quick-release skewers.

Some wheel axles have threads at either end and are secured to the frame with nuts. You’ll find them on track bikes and some fixed-gear bikes.

It is worth mentioning, though, that the term ‘axle’ is actually a bit of a misnomer in these cases. Strictly speaking, none of these bolts or skewers are actually axles, because they are not designed to bear any vertical load. Their primary function is to instead provide a clamping force to ensure a secure connection between the wheel and frame.

Want to know more? We’ve got guides to road bike axle standards and mountain bike axle standards.


Groupset

The groupset includes the mechanical parts that help you get from A to B.
Ian Linton / Immediate Media

Your groupset includes all the mechanical parts that your bike needs to function, in order to get you from A to B.

The definition of a groupset is slightly loose but the core parts are the crankset (comprised of the chainrings and cranks), bottom bracket, chain, cassette, derailleur(s) and shift levers, along with the cables needed to connect them all together.

In addition, it may include your brakes and the cables or hoses connecting them to your levers.

Component makers will sell groupsets with different levels of finish and function, designating them with different groupset series names. Other components, such as pedals and wheelsets, may also bear the groupset’s name, although they’re sold separately.

Groupsets are either mechanical, with cables used for shifting, or electronic, with wires (or wireless signs) used to change gear.

Head to our guides to road bike groupsets and mountain bike groupsets for a deep-dive, while we’ve also got a separate explainer on electronic groupsets.

Drivetrain

The drivetrain is a core part of the groupset outlined above, with the parts that enable you to propel your bike forward. It includes the crankset, chain, cassette, and the rear and front derailleur (if you have one). It excludes the shifters.

Groupset parts explained

Crankset (chainset)

The crankset comprises of the chainrings and cranks, and is often referred to as a chainset.
Russell Burton / Our Media

Your crankset – or chainset in the UK – comprises the two crank arms to which your pedals attach, the chainrings over which your chain runs and the bottom bracket that connects the two arms together.

You may have one, two or three chainrings as part of your crankset, depending on the bike. A crankset with one chainring is known as 1x (‘one-by’).

The crankset sits in the bike’s bottom bracket and turns on bearings.

We’ve got a full guide to crankset sizes and standards, and more information on crank length.

Chain

The chain runs from the crankset to the cassette.
Steve Sayers / Our Media

Your chain connects your chainrings to the cassette on your rear wheel and enables you to propel the bike forward. Most bike chains are comprised of alternating wide and narrow links, which are held together by rivets that pass through their side plates.

In some cases, the two ends of a chain are joined by a rivet, but in others there’s a split ‘quick-link’ that connects them. This can be single-use or in some cases is reusable, so that you can split the chain and rejoin it.

Your chain has to be the right width to work with the number of sprockets in your cassette, but the link spacing is standard across all bikes.

You’ll find some bikes that use a belt-drive in place of a chain.

Our guide to bike chains covers chain dimensions, structure, length, speeds and compatibility.

Front derailleur