Parts Of A Mountain Bike

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.

Frame

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

Bottom bracket

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.

Drop Outs

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.

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.

Rear Suspension

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.

Rear Shock

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.

Bike Wheels

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.

Hubs

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.

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

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

Spokes connect the hubs to the rims. 32 spoke wheels are the most common. There are some 28 spoke wheels as well.

Nipples

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.

Valve stem

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).

Tires

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.

Driveline

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.

Cranks

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.