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Bicycle Components Overview
Illustration of the Most Important Bicycle Components

Bicycle Parts

As simple as a bicycle looks, there are many bicycle parts. These parts may have a different look and feel for the various types of bikes available. As bicycles evolve, these part change shapes and are made with more high tech materials. So, it's important to know the parts, not only for maintenance, but also when you are shopping for a new bike.

The Frame

The frame is the heart of the bicycle. The shape of the frame defines the style of the bike and its intended use. All the other bicycle components are anchored to the frame. Many bike makers are dedicated solely to making frames. They then sell frames in bulk to other brand name companies who then finish building the bicycle and make it available to the public. Good bicycle design begins with the frame.

Parts of a Bicycle Frame
Parts of a Bicycle Frame

  • Frame Geometry

    The tubing on most conventional bike frames is designed to form a diamond shape. This arrangement goes back at least 100 years to the earliest safety bicycles and has not changed much since. The diamond frame's nearly triangular shape (made by the seat, top, head, and down tubes) provides strength; because the triangle is the sturdiest shape for construction.

    The top tube, across the top of the bike, connects the seat area to the steering area. Usually, the top tube runs roughly parallel to the ground, though on step-through bicycles (often mistakenly called "women's bikes") the top tube slopes up from lower on the seat tube. Step-through bicycles are popular with bicycle commuters who might wear skirts, or with those who because of age or other infirmity find it difficult to raise a leg over the top tube.

    The head tube is located just above the front wheel and below the handlebars. It connects the steering system to the front fork, which holds the front wheel. The down tube extends diagonally down from the bottom of the head tube to the bottom bracket (the intersection of the seat tube and the down tube), which is where the crankset (chain-wheel, crank, and pedals) is based. The seat tube connects the bottom bracket to the top tube.

    In addition to the four main tubes, which give the bicycle its diamond-shaped bone structure, the frame consists of two pairs of thinner tubes. Two seat stays connect the point just below the seat, where the seat tube and the top tube meet, to the two sides of the rear axle. Two chain stays connect the same points on the rear axle to the bottom bracket. The area where the seat and chain stays meet at the rear-wheel axle is called the dropout. The seat stay, chain stay, and seat tube form a section of the frame known as the rear triangle.

    The subtle but important variations in frame design come in the area known as frame geometry; how the angles and lengths of the tubes relate to each other. Though all bikes may appear similar in shape, very slight differences in the angles of the tubes can make huge differences in the comfort and performance of the bicycle.

  • Frame Size

    The size of the bicycle frame can be measured in inches or centimetres. The measure is typically the length of the seat tube, from the center of the bottom bracket to the top of the seat lug. However, some bike companies (usually foreign companies) measure the frame size as the length of the seat tube from the center of the bottom bracket to the center of the top tube. The difference between the two styles of measurement will be about 1/2", which is a lot in the precision world of cycling design, so make sure you know how size is being measured.

    The most desirable characteristics in bike parts are light-weight and strength. Materials should also be sufficiently rigid, meaning they'll keep their shape and will not give way under stress, and non-corrosive. While a flexible bike is valued by most riders, suspension should be provided through design (or through the use of shock absorbers and tires), not through the frame material.

  • Bicycle Frame Materials

    For more than a century, steel was the standard material in the making of bike frames. But today, most frames are aluminium, and many other higher-end bicycles are made with lighter-weight carbon fibre and composites, and titanium. Depending on who you are and what your normal ride is like, the choice of bicycle frame is a customized quest. Visit several bicycle shops and ask lots of questions before making the final decision.

The Seat

The bike seat or saddle is attached to the seat post, which extends out of the seat tube above the top tube. Bicycle seats are highly variable. At one extreme you have a cruiser or comfort seat that is very wide and cushy. At the other extreme you have racing seats, which are very narrow and even aerodynamically shaped. So, the seat are designed to fit the style of riding you will pursue.

The Steering System

The steering system is made of a few parts held together in the head tube. The stem extends out above the head and typically bends outward to hold the handlebars.

The Wheels

While wheels vary considerably in weight and size depending on the type of bike, all bicycle wheels have a hub at the center where the wheel axle is located. The axle connects to the bike frame in the front by means of the fork (at the fork ends) and in the back by the seat stay and chain stay.

A bicycle wheel is made up of a rim, spokes, and a hub, with a tire and inner tube secured to the rim. The bicycle shell, which is light and yet supports heavy loads, is quite an engineering accomplishment. However, both wheels of a bicycle need to be perfectly true (flat and un-warped) and aligned to maintain balance and efficient handling.

  • The Hub

    The hub is at the center of the wheel and surrounds the wheel's axle. While the axle is fixed and bolted to the bike frame, the hub turns the wheel around the axle through the use of ball bearings. At the sides of the hub, just inside of the axle connects to the frame, hub flanges flare out to form flat disc surfaces that contain holes for the spokes.

  • Spokes

    Spokes are needed on a wheel to connect the rim to the hub, to provide support for the wheel, and to absorb forces (of both the road and the rider) exerted on the wheel. However, unlike the spokes of a wagon wheel, bicycle spokes hold the wheel together through tension (by pulling in the rim), not through compression (holding the rim in place. Tighter spokes make for stronger wheels.

    Spokes are made of stainless steel and have nipple heads at the end for attaching to the rim and tightening. At the hub, spokes attach to one of the hub flanges, alternating between right and left sides. Wheels may have radial spokes, tangent or crossed spokes, or a combination of the two. Radial spokes simply connect a point on the rim to a point on the hub and do not cross each other, while the stronger tangential spokes wrap around the hub and connect to two points on the rim. crossing other spokes in the process. Most bicycles wheels have 20-36 spokes.

    Some aerodynamic wheels used for racing do not use traditional stainless steel wire spokes. Instead, they may have 2-8 blades made of a composite material. Or, wheels may be solid discs with no spokes at all. While these Aero wheels have less wind resistance, they are heavier and more difficult to make true if bent.

  • The Rim

    Rims are most often made of aluminium. Higher-end rims used for racing are made with carbon fibre. Rims are generally flat on the inside with a concave groove, or tire bed, on the outside. The rim is lined with holes the spokes run through. The spokes are fastened by tightening nipple. Spokes will often become loose, causing the wheel to come out of true. This is easy to remedy with a special spoke wrench, tightening nipple so each spoke in the wheel is at equal tension.

  • Tires

    Most bicycle tires are clinchers, which have metal or Kevlar wires along the edges that hook into a deep-bedded rim. A tire is made of several layers of fabric, reinforced with a puncture-resistant Kevlar layer or threads, which is then coated with rubber and shaped with a tread pattern. A separate inner tube, usually made of synthetic rubber, fits inside the tire.

    Tires, of course, need to be properly inflated to work. Higher-pressure tires generate less resistance against the ground and roll faster. For suspension purposes. though, lower-pressure tires provide a smoother ride. In addition, an effective tread pattern makes tires more stable on the ground and less likely to skid. While some racing bikes reduce friction by having no tread at all, off-road bikes perform better with large treads that grip the ground.

The Drive-train

The drivetrain starts with the pedals, which is where the power source (the rider) meets the locomotive mechanism. The pedals are held in place by the cranks, which are strong bars that jut out of the chainwheel. The chainwheel is the set of circular gears, or sprockets (on the right side of the frame).

At its center, called the crank spindle, the chainwheel connects to the bottom bracket of the bike and turns by means of ball bearings. The chain runs around the sprockets of the chainwheel and connects around the back wheel's axle at the freewheel, or cassette, which has sprockets of its own, called cogs. The freewheel, or cassette, attaches to the back wheel's hub, turning the back wheel whenever the chain moves; which in turn makes the bike move.

The Gears

Most bikes have a gear system that allows riders to adjust pedalling difficulty by moving the bike chain onto larger or smaller sprockets. Gears on most bicycles are operated by mechanisms called derailleurs; some bicycles use an internal hub to change gears. Derailleurs move the chain sideways onto the desired sprocket wheel. They are activated by gear levers, which are shifted by hand, located most frequently on the handlebars, generally incorporated with the brake levers.

The Brakes

Brakes are operated by brake levers located on the handlebars. The brakes levers connect to brake cables that extend to the brakes near the top of the front and rear wheels (rim brakes) or a disc mounted on the hub (disc brakes). Some bicycles use drum brakes operated by levers, or a coaster brake that enables the rider to stop the bike by pressing backward on the pedals.

The Ball Bearings

Though hidden from sight, tiny ball bearings are used in bicycles and play a crucial role in how bicycles operate. In fact, bicycles and ball bearings go way back. Those little hard steel spheres, used in countless applications throughout this century, were first invented for use in bicycles back in the mid-1800s.

Ball bearings are used in the hubs of the wheels as an interface between fixed parts (the axles) and moving parts (the wheels). Because ball bearings significantly reduce the resistance exerted on a bike and the friction between wheels and frame, these tiny metal balls play a larger role than any other bike part in making the bicycles an efficient vehicle.

In addition, to their use in the wheels, ball bearings are used in the head tube for steering, in the crankset to allow the chainwheels to spin while they're held by the bottom bracket, and in the pedals to allow rotation around the pedal axle. So that ball bearings generate the least amount of friction and resistance, grease is used as a lubricant between the balls and the rolling surface.

The Headset

The headset uses ball bearings to enable steering. The handlebar stem locks into the head tube at the upper headset and connects with the fork shaft, or steer tube, inside the head tube. The fork shaft then exits the head tube at the lower headset, splits, and extends down to connect to the front wheel. While the head tube remains fixed, the steering system turns due to the ball bearings in both the upper and lower headsets.

The Transmission

Transmission refers to the parts of the bike that make it go. Besides your own feet, the transmission includes the bike's drive-train and the gear system.

  • The Crankset and Pedals

    The crankset consists of the chainwheels, which revolve around the bottom bracket by means of a spindle, and the cranks, which are the arms that turn the chainwheels. Pedals are attached to the cranks. The bottom bracket spindle uses ball bearings to turn the crankset in the fixed bottom bracket. Most bikes with variable gears have two or three chainwheels (a double or triple crankset) and increase in size as they move away from the bike. Each chainwheel has teeth on which the chain is threaded. As riders switch gears, the chain moves from one chainwheel to another. Larger chainwheels are responsible for the high gears that are difficult to pedal and that move the bike fast, while smaller chainwheels engage the low gears used to climb hills or start from a dead stop.

    Crankcases, or simply cranks, attach to the bottom bracket spindle. They are fairly standard, with slight variations in length (160-180 mm) and design. Most cranks are suitable as long as they contribute to a rider's proper bike fit (along with frame size and seat height), are strong enough to withstand pedalling force (which is exerted on the crank-spindle connection, and turn the chainwheels effectively. However, slightly longer crankarms will give the rider more leverage in climbing hills and more pedal power on level surfaces. There is a limit to how long crankarms can be, though. They must be short enough to allow ample clearance between the pedals and the ground at all times.

    Crankarm ends attach to the pedals at the pedal axle, the midpoint on the inside of the pedals. Pedals rotate around the pedal axle through the use of ball bearings. The movements of the pedal independent to the crankarms enables riders to keep their feet planted on the pedals throughout the 360-degree pedal stroke and to get the proper leverage for maximum pedalling efficiency. A few different types of pedals are commonly found on bicycles. The ordinary flat pedals come in a variety of shapes and degree of traction. Many pedals used for higher performance bicycling are called clip-less, which require special shoes with cleats attached to the sole that clamp into the pedal. Clipless pedals improve pedalling efficiency by holding the feet on the pedal to provide more stability and power in the pedalling upstroke. Most cleats used with clipless pedals detach easily when a bicyclist needs to slow or stop, usually by moving the heel of the foot away from the pedal.

  • The Chain

    Chain design is standard in almost all bikes and has remained largely unchanged for many decades. Some higher-performance chains intended for racing have become more narrow, and require special cranksets and cassettes. The tooth-and-link chain is made of two parallel sets of steel-link plates with cylindrical rollers between them at the joints. The teeth of the chainwheels are rear cogs thread into the space between the rollers. A light lubricant is needed to keep the chain running smoothly, and the chain should be kept free of grime, dirt, and rust.

    For the chain to run properly, chainwheels and cogs should be directly in line and centered. Gear settings that require the chain to deviate most (for example, a setting that uses the outermost chainwheel and the innermost cog) cause more ear more wear on the chain and decreased pedalling efficiency. A chain tool is used to disconnect the chain from the drive-train, by pushing out an individual pin from a joint. Some chains can be broken and reattached with special chain links.

  • Freewheel and Cogs

    Most bicycles come with rear cassettes, with the freewheel mechanism incorporated into the rear hub. The freewheel is the mechanism attached to the rear axle that allow (with the help of ball bearings) the rear wheel to turn without the rider having to to pedal (known as coasting). Coasting is accomplished when levers, or pawls, in the freewheel that work to engage the wheel during pedalling will disengage (causing that familiar clicking sound) during coasting.

    Usually installed around the freewheel are a series of cogs, or sprockets, similar in appearance to the chainwheels on the crankset, but smaller in size and more numerous. Like chainwheels, cogs are located on the right wide of the wheel and progress in size, though cogs get smaller as they move away from the rear wheel. The chain, which is threaded onto the chainwheel in front, wraps around the teeth of a cog on the rear. as riders switch gears, the chain moves from one cog to another. Unlike the chainwheels (which work in the opposite way), the larger cogs make pedalling easier, while the smaller ones give you more power.

  • Gears

    The gears of a bicycle simply refers to the position of the chain. It will always be threaded on one of the 2-3 chainwheels in front and one of the 7-10 cogs in the rear. The number of gears or speeds a bike has is equal to the number of possible combinations of chainwheel and cog settings. It can be determined by multiplying the number of cogs by the number of chainwheels. For example, a bike with eight cogs and three chainwheels will have 24 gears or speeds.

    While, the sizes of gears increase relative to each other, the measurable size of chainwheels and cogs, and the range between the gears, vary from bike to bike. Some bike have extra small gears designed for hill climbing, while other bikes lack smaller gears. Because the teeth on cogs and chainwheel are of a standard size in order to fit with standard chains, the size of a cog or chainwheel is often measured by the number of teeth it has. For instance, a 40T cog will have forty teeth.

    Difficulty in peddling, however, is not a matter of the individual sizes of the cog and chainwheel used, but rather of the ratio of the two together. That is, the combined size of a midsized cog and chainwheel may be equal to the combined size of a small cog and large chainwheel, but the two settings will not provide equal difficulty in pedalling because the gear ratio of the latter is much greater than the former (and therefore makes the bicycle more difficult to pedal).

  • Derailleurs and Shift Levers

    Shift levers located on the handlebars regulate the switching of gears. Most bicycles have two levers; one that moves the chain between the chainwheels in front (typically the left lever) and one that moves the chain between the cogs in back (typically the right lever). The levers connect to the derailleurs, which physically shift the gears through flexible cables that run along the bike frame.

    The rear derailleur is typically attached to the dropout (near the rear wheel axle) with a pivot bolt that allows it to move lengthwise along the rear drivetrain. Most rear derailleurs have two chain-guide wheels through which the chain is threaded. Moving the gear levers causes the cables to be pulled or released, thus either pulling the derailleur in toward the wheel or allowing it to move farther away from the wheel. As the derailleur moves, it takes the chain with it, causing the chain to move to a larger or smaller cog, thus switching gears.

    A spring mechanism causes the derailleur to swing backward, to pick up the chain slack as gears are shifted to smaller sprockets, and forward, to compensate for the additional chain needed as gears are shifted to larger sprockets. Therefore, how far the rear derailleur is able to swing back and forth determines the largest and smallest sizes possible for the chainwheels and cogs.

    The front derailleur is located above the crankset and is typically attached to the seat tube. Much as with the rear derailleur, the chain runs through a piece of the front derailleur, the chain runs through a piece of the front derailleur called the cage, which is responsible for physically pushing the chain from one chainwheel to another. Gear shifting on the front end is also accomplished by pulling or relaxing a cable connected to and manipulated by the gear levers.

    While all derailleur gearing works on essentially the same principle, index derailleurs are preferable to conventional derailleurs because they offer more precision in shifting. For index shifting, the exact amount of cable pull needed to move the derailleurs (and chain) to each cog or chainwheel is preset, and gear shifters are clicked into each gear. Cables for index shifting are thicker and stronger so that they stay perfectly adjusted.

Suspension

All bicycles have some kind of suspension to protect them and the rider from felling every bump on the road or trail. otherwise, bikes would feel like the old bone-shakers of the nineteenth century. Good suspension protects the bicycle from the wear and tear of the road, increases traction by keeping the wheels on the ground, and makes the rider more comfortable. Pneumatic tires provide basic suspension, and additional suspension can be built into a bicycle either directly through shock absorbers or indirectly through design. Some bikes, particularly off-road bikes, have spring-loaded steel coils in the forks that absorb bumps and jumps and works like a car's shock absorbers. Other bikes have shocks built into the rear triangle of the frame, either on the seat stay or seat tube. Less often. bikes can be found with springs or other suspension systems built into the saddle or handlebars, though these create unwanted variables in bike fit. Fork shocks, the most common kind, have become a very popular component on many bikes in recent years.

Most bikes, especially road bikes, don't have shock absorbers. Instead, a milder form of suspension is built into the bike's design. Suspension is increased through a wider wheelbase; larger fork rake; and larger, fatter tires. Then, the inflation of air in tires can be adjusted for ground conditions. While this kind of suspension is certainly not as effective as a shock absorber, it is certainly adequate for bikes rolling on smooth pavement.

There is one other method of suspension that riders use to ease the shock of surface bumps: movement of their bodies. By standing up as they go over bumps, they are essentially using their legs as suspension.

Brakes

The three main types of braking systems used in bicycles today are calliper brakes, cantilever brakes, and disc brakes. Calliper and cantilever brakes apply pressure on the rim of the wheel to stop the bike and considered rim brakes. Disc brakes apply pressure to metal discs attached to one side of the wheel hub.

All three types work through a system of levers and cables. Cables connect the brake levers (located on the handlebars) to the brake arms that surround the top of the wheels and are secured to the fork in front or seat stay in back. When the levers are flexed by hand, the cables pull, closing the brake arms around the rims or disc. When the levers are released, the brakes spring back to their home open position.

The section of the brakes, called brake pad, or brake shoe, that comes into contact with the moving surface (rim or disc) is usually made of rubber or composite material to maximize friction needed to stop. All other parts of the braking system, including arms, cable, and levers, must be ridged and precisely positioned to transfer the relatively light force exerted by hands on brake levers to the high power needed in the brakes for effective braking.

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