Bike Anatomy: A Complete Glossary + Diagrams!
When broken down into smaller parts, bicycles are pretty simple machines. There are two wheels, some gears, pedals, and a way to steer in a straight line. But like most things, even though they’re ‘simple’ there are still a lot of terms and concepts to learn about them, especially when it comes to bike anatomy.
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In this post, I’ve compiled a glossary of common bike anatomy terms, along with accompanying diagrams, to help you understand everything from gears to handlebars. I even learned a few things myself while doing the research!
Learn the basics of bike anatomy including common terms, where components are located, and more!
Big Picture View Of Bike Anatomy
Braze ons
Braze ons are basically anything that is permanently attached to a bike frame such as water bottle cage mounts or rack mounts.
Down tube
The down tube on a bicycle is the tube that connects the head tube to the bottom bracket. It is typically (but not always) thicker than the other tubes on the bike and it plays a key role in determining the strength and stiffness of the bike.
Dropouts
Where the bike wheels fit into the frame.
Bottom Bracket
The bottom bracket is what allows your crankset (see groupset bike anatomy parts below) to rotate freely. In other words, the bottom bracket allows you to pedal. It consists of several parts: the spindle that the crank arms are attached to, the bearings themselves, and usually a dust cover.
The bottom bracket sits in a shell that’s threaded on both sides and held in place by either bolts or screws.
Chainstay
The chain stay is the part of the frame that supports the rear wheel and it plays an important role in keeping the bike stable, especially at high speeds.
Fork
The front fork of a bicycle holds the front wheel in place. It is attached to the frame via the head tube and headset. There are several different types of forks. A mountain bike fork will have suspension (either air or coil) while road bikes have a rigid fork with no suspension.
For more details on mountain bike forks, see the mountain bike anatomy sections below.
Handlebars
These are pretty self-explanatory, but the handlebars allow the rider to steer their bike. The handlebars are attached to the bike by the headset, which also connects the handlebars to the front fork.
Headset
The headset on a bicycle is the part of the bike that holds the fork in place. Without a headset, a bike would not be able to turn. The headset also allows the rider to steer the bike.
Head tube
The head tube on a bicycle connects the fork to the frame. It is an important structural component of the bicycle and often determines how a bike handles on the road or trail.
A steep head tube angle means that the fork will be more perpendicular to the ground while a slacker head tube angle means the fork will be at an angle with the front wheel farther out in front.
Rails
The metal tubes underneath a saddle that are the attachment points to the seat post.
Saddle
Where your rear end sits.
Seat post
The seat post is what supports the saddle. Without it, you would have nowhere to sit while riding! Seat posts come in several different styles including dropper posts for mountain bikes or an adjustable clamp-on seat post for cruiser bikes.
Seat stay
The seat stays help support the rear end of the bike and forms the rear triangle along with the chain stay.
Seat tube
The seat tube on a bicycle is the part of the frame that supports the saddle. It is usually the longest tube on the frame, and it extends from the bottom bracket to the top of the seat post.
Like head tube angles, seat tubes can either be steep or slack depending on the type of bike and what kind of riding you will be doing. Steep seat tube angles typically make pedaling easier and more efficient.
Steer tube
The steer tube is the tube that sticks up straight from the fork and connects to the headset (and thus the stem and handlebars), allowing the rider to control and steer the front end of the bike.
Stem
The stem on a bicycle is what connects the handlebars to the frame. Depending on the style of bike, the stem can be integrated into the frame or it can be a separate piece that’s attached with bolts.
Stems also vary in length. Road bikes tend to have longer stems than mountain bikes.
Thru-axels
Cylinders that slide through the front and rear hubs and attach the wheels to the bike.
Top tube
The top tube on a bicycle connects the seat tube to the head tube. It is typically horizontal, but it can be angled upward or downward. Some top tubes, like on beach cruisers, can also be curved so that the rider has an easier time getting on and off the bike.
bicycle Groupset Anatomy + Derailleur Parts
B Tension Screw
The B Tension Screw on the derailleur adjusts the distance between the upper jockey wheel and the largest cog on the rear cassette. If this measurement is off, the derailleur can get caught on the rear cassette, which is no bueno.
Calipers
The part of brakes that squeeze the pads onto either the rims or the rotors. Basically the ‘housing’ of brake pads.
Cog
A cog is one ring on the rear cassette.
Cog teeth
Each cog has a number of ‘teeth’ that fit into each chain link. This pairing allows the chain to drive the bike forward when pedaling.
Chain
One of the most important parts of bike anatomy is the chain. The chain helps to power the bike and keep it moving forward.
Chain link
The chain is made up of individual chain links.
Crank arms
Crank arms transfer the power from your legs and pedals to the bike’s chain. They are attached to the frame via the bottom bracket.
Derailleur
The derailleur is what allows your bike to shift through gears. Some bikes (like most new mountain bikes) only have a rear derailleur while road bikes usually have a front derailleur and 2-3 front chainrings.
Derailleur hanger
The derailleur hanger is the piece of metal that attaches your rear derailleur to your bike frame. A derailleur hanger is actually designed to break or bend during a crash because a derailleur hanger is much less expensive to replace than a full derailleur.
Derailleur hangers are bike-specific and it’s always a good idea to carry a spare derailleur hanger in your pack or bike tool kit.
Disc brakes
A system of brakes that uses calipers to squeeze a pair of brake pads onto a metal rotor, which slows down the revolution of the wheels.
Disc brakes use fluid to put pressure on pistons in the calipers that then squeeze the brake pads together.
Front chainring(s)
The chainring(s) are at the front of the drivetrain and are connected to the crank arms. Some bikes only have one front chainring (called a 1x) while other bikes have 2 or 3. The more front chainrings a bike has, the more gears it has.
Groupset
Refers to the moving comments of a bike that include the shifters, chainset, cassette, derailleurs, brakes, bottom bracket, chain, and cables.
Housing
The plastic tubing that encases shifting cables and disc brake fluids.
Limit screws
The limit screws on a bike allow you to adjust the position of the rear derailleur in relation to the rear cassette. Limit screws that are off can cause the chain to fall in between the cassette and the spokes or in between the cassette and the chainstay.
Jockey wheel
The jockey wheels help guide the chain through the derailleur.
Pistons
Small moving parts inside disc brakes that enable the brake pads to make contact with the rotors to slow you down.
Rear Cassette
The rear cassette is the group of cogs (rings) on the rear wheel. The more cogs you have on your rear cassette, the more gears you have.
Rim brakes
A system of brakes that uses cables to squeeze brake pads directly onto the rims of the wheels. Rim brakes are less common now that more people are adopting disc brakes, which are stronger and more efficient at stopping.
bike wheel components
Hub
The hub on a bicycle is the central point around which the wheels rotate. They’re connected to the wheel via the spokes and a thru-axel and spin freely via bearings.
Nipples
Nipples are small nuts that attach spokes to the rim of the wheels.
Rims
The rim on a bicycle wheel is the supporting structure that helps keep the tire in place. It also helps to provide stability and strength to the structure of the wheel as a whole.
Rotors
Rotors are only found on bikes with disc brakes. They are attached to the front and rear wheels and are part of the disc brake system. When brake pads are squeezed onto the rotor, the revolution of the wheel slows, allowing the rider to slow down or stop.
Spokes
The spokes on a bicycle wheel provide support and keep the wheel from collapsing.
Tire
A bicycle tire is essentially a round rubber tube that is designed to grip the road or trail and provide traction. There are many different sizes and widths of bicycle tires depending on what type of bike you’re riding and what your riding goals are.
Mountain bike Anatomy
The bike anatomy I covered above can be applied to most bikes whether it’s a road bike, mountain bike, gravel bike, or simple cruiser.
However, mountain bikes have a few extra parts that are worth mentioning, especially if you plan on doing your own bike maintenance.
Bike fork parts
Arch
The piece of plastic that connects the two lower fork legs
Dust seals
These are seals that help prevent dirt and grime from entering the lower fork legs. They’re located at the top of the lower fork legs where they meet the stanchions.
Lower fork legs
This is the lower portion of the front fork on a mountain bike. The stanchions slide down into the lower fork legs as you ride over trail obstacles to create suspension.
Stanchions
Stanchions on a mountain bike are the ‘exposed’ part of the fork suspension. These tubes slide down into the lower fork legs and also house the inner suspension components such as the damper and air shaft or coil.
Pivots
These are basically junctures in the mountain bike frame that can flex and move in response to the workings of the suspension. Pivots typically work via bearings.
Rear shock
Rear shocks are found on full-suspension mountain bikes and they help absorb bumps and shocks to make the ride smoother.
What questions do you still have about bike anatomy? What terms would you add to this list? Drop a comment below!
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