Mountain bikes have become more and more complex over the past years. The terminology can get confusing. What are people talking about when they mention dropper posts or cassettes? Let’s cut through some of the confusion and help you get to know your mountain bike. Here is a guide to all the parts of a mountain bike.
Guide to all the parts of a mountain bike
At the heart of your mountain bike is the frame. This is what makes your bike what it is. Everything else is ad on components. Most frames consist of a top tube, head tube, down tube, chain stays, seat stays, bottom bracket and drop outs. There a are some exceptions where a frame will have less tubes but they aren’t common. The seat stays and chain stays in a full suspension bike are part of the rear suspension linkages.
The most common material for bike frames these days are steel, aluminum and carbon fiber. There are a few bike frames made from titanium as well. Carbon will be the lightest and steel will be the heaviest. See my article on how much does a good mountain bike weigh for more information.
The bottom bracket houses the bearing that support the crank. There are several standards for bottom brackets such as BB30, Square Taper, DUB, Pressfit and Threaded. Cranks will only work with compatible bottom brackets. You need to find out what kind of bottom bracket you have before trying to buy replacement or upgrade cranks. For more information on bottom bracket standards and types see this guide by Parktool.
Drop Outs are where the rear wheel attaches. They will either be setup for a thru-axle to thread into them or a slot where a quick release axle can slide up in.
Head Tube Angle or Slack Geometry
There is a lot of mention these days of a bike being “More slack” or having “more aggressive geometry”. This is referring to the head tube angle of the bike. A bike with “more slack” geometry has a slacker head tube angle. This makes the bike more stable at higher speeds. It makes is less agile in really tight single track. See the below diagram. Go here to learn more about mountain bike geometry and it’s effect on handling.
Front Suspension Fork
Most mountain bikes have a front suspension fork. Suspension forks can have travel that varies from 100mm to 160mm. Cross country bikes will use smaller travel. Downhill bikes will use as much travel as they can get. Suspension forks smooth our the terrain and let you have more control. Some mountain bikes, such as fat bikes, have traditional rigid forks. Fat Bikes with really wide tires have enough cushion in the tires that front suspension isn’t that necessary.
Front suspension forks can have many different spring and damper setups. There are really inexpensive forks that are just a mechanical spring. Most middle to high end mountain bikes will have air springs with dampers. They may also have a lockout that prevents the suspension from travelling. This is useful for climbing or riding on smooth surfaces where suspenion isn’t needed.
Many mountain bikes have full suspension or rear suspension. This means they have a linkage system in the seat and chain stays and a rear shock absorber. Travel can vary from 100mm to 160mm similar to the front suspension fork. The linkage can be a simple single pivot or a a 4 bar linkage on more sophisticated systems. There are many different rear suspension styles. FSR from Specialized and Mastro from Giant are 2 of the more common linkage geometries.
Full suspension will add a couple of pounds of weight to a bike. It will give you more control and comfort for the weight and efficiency loss. See my article on full suspension bike weight to learn more.
Rear shock absorbers can be really simple mechanical springs or more complicated. Most have air springs with some amount of damping. The rear suspension gets loaded on every pedal stroke. An undamped rear shock will be very poor for climbing and will feel like riding a pogo stick. Rear suspensions can have lockouts similar to front suspensions.
The wheels on your bike are what make it a mountain bike. Wheels are made of hubs, spokes, rims, and tires. Most mountain bike these days have disc brakes and the rotor is also attached to the hub. Wheels can vary from inexpensive factory wheels to high end custom carbon fiber wheels. To learn more about getting custom wheels, see my review of Cyclewheels USA custom wheels.
The hubs are at the centers of the wheels. They house the axles and bearings. The wheel spokes attach to the hubs. The brake rotors also attach to the hubs.
The freehub us found on the rear wheel and contains the ratchet mechanism. This allows you to pedal going forward and for the wheel to spin freely coasting when your not pedalling. There are a few different body styles for the freehub. The most common is Shimano Hyperglide followed by SRAM XD Driver and Shimano Microspline.
Disc Brakes Rotors
Most modern mountain bikes have disc brakes. These use calipers and rotors. The rotor mounts to the hubs. They attached with either a 6 bolt pattern or a clincher attachment. There are a few common rotor sizes. 160mm, 180mm and 203m.
Quick Release or Thru-Axle
Mountain bike wheels are attached to the frame and fork with either a quick release axle or a thru-bolt axle. Quick release axles have a release lever that cinches the axle tight. Thru-axles have a threaded axle with a lever that you tighten them with. Both look similar from a quick look.
Rims are the outer part of the wheel that the tires mount too. Most mountain bike rims are made of aluminum or carbon fiber. Rims can be different widths depending on their use.
Spokes connect the hubs to the rims. 32 spoke wheels are the most common. There are some 28 spoke wheels as well.
Nipples connect the spokes to the rims. Spokes are threaded into the nipples. Spoke tension is adjusted by turning the nipples. Spoke tension is used to true or remove wobbles from the wheels.
You will have a valve stem on each wheel for inflating or deflating tires. You will either have Presta valves (mid to high range bike) or Schrader valves (low end bike). See my article on Presta vs Schrader Valves to learn more.
Tires are mounted to the rims. Mountain bike tires come in many varieties and widths. Tires can be designed for cross country racing or downhill use or anywhere in between. Tires make a huge difference in how your bike handles. It’s a good idea to find out what the most popular tires are for the trails in your area. See my article on when to replace mountain bike tires for more information.
The driveline on your bike is how you get your leg power to the wheels. 1x drivelines with only a single front chain ring are the most common on mid to high end mountain bikes. They are quickly becoming the standard on cheaper bikes as well.
For more information, see my article on 1X drivelines for mountain bikes.
The cranks transmit power from your pedals to the chainring. They go through the bottom bracket at the bottom of your frame. The bottom bracket contains the bearings that support the crank loads. Cranks can be made from aluminum, steel, carbon fiber or titanium. Aluminum or steel are the most common.
The cranks contain the attachment and mounts for the chainring or chainrings.
Pedals are what you push on with your feet. There are 2 main pedal types used on mountain bikes. Flats or Platform pedals and Clipless pedals. Flats or platform are the traditional pedal everyone knows. It’s a flat pedal you push on with regular shoes. Clipless pedals are pedals with a cleat that clips into the pedal.
Clipless pedals are a bit of an oxymoron because you clip into them. It comes from way back when the first clip-in pedals had a clip you had to hook to your shoe. Clipless was the new advance in technology that you only had to step and click into without clipping anything.
The chainring transfers the power from the cranks to the chain. Most mid to high end mountain bikes have only a single chainring. A mountain bike can have up to 3 chainrings. Smaller chainrings make climbing easier. Larger chainrings let you go faster at higher resistance. Oval chainrings are also available. These smooth out the pedalling effort. I personally use an oval ring and like it a lot. It’s a personal preference thing.
If your mountain bike has 2 or 3 chainrings that it will have a front derailleur to switch between them. It will be cable operated from a shifter on your handlebar. Front derailleurs are one of the most difficult components on a bike to adjust. If yours isn’t shifting smooth and you can’t quite seem to make it work right, don’t feel bad. You’re not alone. It’s a big reason why many of us got rid of it for 1X setups.
Front derailleurs shift from the tension load side of the chain. It’s best to shift chainrings before you start climbing a steep hill. If you try to shift while pedaling really hard, you will put a lot of tension in the chain while pushing with the derailleur. It’s very easy to brake parts doing this.
The rear derailleur shifts cogs on the cassette. The rear derailleur shifts from the slack side of the chain. They are more tolerant of shifting under load than a front derailleur. They can come in short cage or long cage versions. Longer cages can handle more difference between the smallest and largest cogs. A 12 speed bike with 10-50 tooth cogs will need a long cage derailleur where a bike with 7 cogs from 11-36 teeth will not.
Some rear derailleurs are referred to as clutch derailleurs. These derailleurs have stiffer springs to keep more tension in the slack side of the chain. This is for 1x drivelines. It helps prevent the chain from dropping. Shimano clutch derailleurs have a level to release the clutch and tension. SRAM clutch derailleurs have a service pin you can push in to release tension on the chain.
The cassette is the set of rear cog gears. Mountain bikes have between 7 and 12 rear cogs. The latest trend in mountain bikes is 12 speed 1X drivelines. Cassettes are made to work with a certain type of freehub body. A Shimano Hyperglide cassette will not fun on a XD driver rear hub.
Some low end mountain bikes have a freewheel in their cogs instead of a cassette. A freewheel is a combined cassette and freehub in one. You will only find it on bikes under $500 with 7 cogs.
The chain connects and transfers power from the front chainring to the cassette and rear wheel.
Most mountain bikes from mid to high end have disc brakes. Disc brakes are similar to car disc brakes or motorcycle disc brakes. They have a caliper mounted to the frame or fork and rotors mounted to the wheels.
Disc brakes can be either cable operated or hydraulic. It is rare to see cable operated brakes on mountain bikes that cost above $600. Hydraulic disc brakes can give you a lot of stopping power with very little finger effort. The calipers can have 2 or 4 pistons. The rotors can be between 160 and 203mm in diameter. 4 piston calipers with 203mm rotors will have more stopping power than 2 pistons with 160mm rotors.
On low end mountain bikes you can still find v-brakes or u-brakes that work by clamping against the rim. They are not as good as disc brakes for many reasons: They need more finger effort, they don’t work when the rim is wet, they are affected by out of true rims.
The cockpit of your bike is the handlebar and stem and everything mounted on it. All of the stuff you use to control your bike while your riding it. This can be more or less items depending on your bike. Some bikes have lockouts, droppers, and other things mounted on the handlebars in addition to shifters and brake levers.
Handlebars are what you steer your bike with. They come in varying width and amounts of rise and sweep. Crosscountry race bikes tend to have flat bars with no rise and little sweep. Trail bikes or recreational bikes tend to have more rise and sweep. Most handlebars are made of aluminum or carbon.
The stem connects your handlebar to your fork and frame. Modern mountain bikes all use a system called an aheadset stem that clamps to the fork steerer tube on one end and the handlebar on the other. Stems come in varying lengths and rise amounts. Most bikes come with aluminum stems that are around 50mm in length.
Headset are the bearings at the top and bottom of your frame head tube. These bearing support the fork and steering loads. The bearing tightness is adjusted by tightening the cap on top of your stem before tightening the stem to the steering tube. You shouldn’t have any play in your steering tube relative to your frame.
Shifters control the front and rear derailleurs to shift gears. The rear derailleur shifter will be on the right side and the front derailleur (if you have one) will be on the left side. Most mountain bikes have push button shifters. These work by pushing a button to shift up or down. There are a few bikes that have grip or twist shifters that work by twisting the grip on your handlebar to shift.
Brake levers are mounted to your handlebar. The front brake will be on the left and rear brake on the right.
Other cockpit items on handlebars
There are many other things that can be mounted to the stem and handlebars. Some common items are dropper post levers, suspension lockouts, GPS mounts, etc…
The saddle is seat is what you sit on. Seats come in many varieties. For short rides, thick seats with lots of padding are good. For longer rides narrower seats with thinner foam are better.
For proper fit you should measure your sit bones and get a seat that is wider.
Seat post or Dropper post
The seat post connects your saddle to your bike frame. Standard seat posts are fixed length and adjustable by sliding them in and out of the frame.
Dropper posts are a seatpost that you can change the height of while riding. They have a release lever that lets you push the seat lower. This is helpful for riding technical downhill features or jumps. When you want a full height saddle you push the release lever and let the dropper post extend.
For those wanting a video guide to all the parts of a mountain bike, watch the video below. It gives a 5 minute look at most of the parts on a mountain bike.
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- How Much Does A Good Mountain Bike Weigh? Is It Important?
- The Best Mountain Bikes Under $600 Helpful Guide
- Outbound Lighting Downhill Package Review – Great Trail Riding Lights
Co-Founder & Chief Editor
I grew up back east in Pennsylvania and learned to ski on a family trip to Killington, Vermont when I was 6. I immediately fell in love with the mountains and outdoors and have been skiing across the US and Canada ever since. I went to school for Mechanical Engineering, and have a Master’s Degree in Material Science and Reliability.
I am a total gear nerd and love learning how things work and thinking about how they could be improved. Nothing excites me more than trying out new gear. I’d rather spend 3 hours taking my bike apart and learning how to change something than go to a bike shop. These days I reside in Michigan by the Great Lakes and go skiing, biking, and boating as much as possible.