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Buying a Bicycle -- A Basic Guide: Understanding the Bicycle



Now, we’ll take a look at what all bikes have in common, and define how the various parts differ for different types of machines. Figure 1 depicts a simple mountain bike, labeled with the names of the various parts.

The Parts of the Bike

A bike consists of a frame and a number of components that are installed on the frame. The bicycle manufacturer assembles those parts to the finished frame. Some of the other parts, such as the wheels, themselves consist of a number of smaller separate components that have been assembled before they are installed on the bike.

The various components come from specialized manufacturers. A lot of those parts are supplied by one of a small number of manufacturers of bicycle components. Among those, Shimano is the biggest and most common. This Japanese manufacturer produces whole series of components in many different price and quality categories. A complete package of parts is referred to as a “gruppo” in the U.S., or “group-set” in Britain.

Although everything Shimano makes works quite well, it’s not necessarily an indication of a particular quality level if a bike is referred to as “Shimano-equipped.” Your question should be,

“What quality are those Shimano components?” There are Shimano-made component groups used on the $100 cash-and- carry bike from a discount store, as well as on a $3,000 custom bike, and obviously they’re not the same.

On average, about one half of the total cost of a bike goes into the frame, the other half into the components. Consequently, you can assume that the components mounted on the $100 bike are worth only about $50, while $1,500 worth of components may have been installed on the $3,000 marvel in the window of the upscale bike shop.

The various components can be broken down on the basis of the functional groups they constitute. Besides the frame itself, those are the steering system, the wheels, the brakes, the drivetrain, the gearing system, the seat, and other components (which on many mountain bikes include suspension components).

The conventional bicycle frame is built using tubes that are connected together to form a rigid structure. In addition to the conventional materials of steel and aluminum, other materials, such as titanium, metal matrix, and carbon fiber, are being used increasingly. Unconventional designs are made possible through the use of carbon fiber and similar materials. These are mainly used on high-end mountain bikes, where the use of complex suspension systems creates the incentive to move away from the traditional and familiar diamond-shaped frame design; they are also used on high-end road bikes.

Each of these materials can be made into a light and strong frame. Indeed some steel frames are lighter than many aluminum or carbon fiber frames, and some aluminum frames are as strong as any steel frame. It depends on the type of steel or other material used and how it’s assembled. If you hear a bike is made of “chrome-moly” (sometimes shortened to “cro-mo”), that’s not some magic metal, but one of several types of steel that are suitable for strong and reasonably light frames. The highest quality metal tubing, both steel and aluminum, are butted, meaning that the tubes have thinner walls in the middle than at the ends. This makes for a lighter frame.


FIG. 1. The parts of The bicycle, showing the names for the various components as used in this guide.

The Frame

The various parts of the conventional frame are categorized as main frame and rear triangle. The thick tubes of the main frame are head tube, top tube, downtube and seat tube. The rear triangle consists of pairs of thinner pairs of tubes, called seat stays and chain stays. The bottom bracket is the point at the bottom of the seat tube where it’s connected with the downtube and the chain stays. This is where the bottom bracket (the bearings and spindle for the cranks) is installed. At the top, the rear triangle’s seat stays are attached to the seat tube just below the seat lug, which is the part where the seatpost is clamped in. The most important criterion for the frame is that it must be the right size to match the rider, and that subject will be covered extensively in Section 4, “Sizing Your Bike.” The other aspect to consider is that different kinds of bikes have different frame designs. For example, mountain bikes are not just road bikes with fatter tires, but also call for a specific frame design.

The Steering System

The components that make the bike steer are referred to as the steering system. It consists of the front fork, held in the frame’s head tube by means of a set of bearings called the headset, and the handlebars with the stem that connects them to the fork. Again, these components differ as a function of the bike’s use. For example, road bikes have drop handlebars, while mountain bikes typically have straight, flat handlebars and often suspension forks.

The Wheels

Mountain and cyclo-cross bikes use cantilever brakes. Both types are mounted on bosses (metal attachments with pivot points) permanently installed on the seatstays and the front fork.

Road bikes generally use sidepull brakes, which are installed as complete units to the front fork, and a bridge piece between the seatstays of the frame. In addition, there are brakes built into the hub, as used on the old cruiser and some of the newer incarnations of the utility bike that are just now being introduced, and as disk brakes on downhill-type mountain bikes.

The brakes are operated by means of levers mounted on the handlebars (except coaster brakes, which are operated simply by pedaling back). Again, the type of levers varies with the type of bike, and those for high-end road bikes nowadays are usually integrated with the shift lever mechanism for the gears, and are suitable only for use with drop handlebars. On mountain bikes, the brake levers are specifically designed for use with the mountain bike’s flat handlebars.

The brake levers are connected with the brake mechanisms by means of flexible control cables (unless they are operated hydraulically, as is the case on some downhill-type mountain bikes).

After the frame, the wheels are the main items that characterize a specific type of bike. Fat 26-inch wheels for mountain bikes, skinny 700 mm wheels (nominally 700 mm is about 28 inches, but their actual outside diameter is about 27 inches) for road bikes, slightly fatter ones for hybrids and touring bikes, small ones for folding bikes, and so on.

Each wheel consists of a rim on which the tire and the inner tube are mounted, a hub with bearings around which the wheel rotates, and a set of spokes to tie it all together. The lighter the wheel, the nimbler the ride; the fatter the tires, the better their shock-absorption qualities.

The Brakes

Depending on what type of bike you’ve got, the brakes are somewhat different. On mountain bikes direct-pull brakes (also referred to as V-brakes) are commonly used today. Older mountain bikes, as well as most hybrids, touring bikes, tandems,


FIG. 2. Steering system on a mountain bike with front suspension.


FIG. 3. Drivetrain/gearing on a mountain bike.

The Drivetrain

The drivetrain is the set of components that transmits your leg motion to the rear wheel. Although the gearing system components are sometimes considered part of the drivetrain too, I will treat those separately below.

The cranks are attached to the bottom bracket spindle that runs on bearings in the frame’s bottom bracket (sometimes called “BB” for short). Chainrings of different sizes are attached to the right crank, and the pedals are screwed onto the ends of the crankarms. Upscale pedals are clipless, meaning— paradoxically—that they clip onto special shoes, whereas simpler bikes have pedals that can be ridden with any shoes.

The other parts of the drivetrain are the chain and the cogs on the rear wheel’s hub, as well as the freewheel mechanism on which the cogs are mounted.

The Gearing System

Except for some recently introduced utility bikes and old-style cruisers (and, in England, three-speed roadsters), modern bikes have derailleur gearing. This system simply shoves the chain sideways from one combination of front chainring and rear cog to another. Since the differences are in the number of teeth on chainring and cog respectively, the result is that the same pedaling speed is translated into a higher or lower rotating speed for the rear wheel. The theory and practice will be explained in Section 8, “Using the Gears.”

The rear derailleur is mounted to the right of the rear wheel hub and is controlled from a shifter on the right side of the handlebars. The front derailleur is mounted to the right of the frame’s seat tube, just above the chainrings, and it’s controlled from a shifter on the left side of the handlebars.

The type of shifter depends on the type of bike. On most mountain bikes, they are mounted under the handgrips, or sometimes a twistgrip is used, on which the shifting mechanism is combined with the handgrip. On hybrids, twistgrips are used most frequently. On high-end road bikes, the shifters are usually integrated with the brake levers. On touring bikes and some road bikes, the shifters may be either on the ends of the drop handlebars or on the side of the frame’s downtube. The new crop of internal-hub—geared utility bikes uses either a single twistgrip or a shift lever mounted under the handlebars. Whatever type, the shifters are connected with the matching mechanism by means of a flexible cable similar to that used to control the brakes.

The Saddle

Also referred to as the seat, the saddle is attached to the frame by means of the seatpost, which is clamped into the frame’s seat lug. The height can be varied by loosening this connection and tightening it again at a different point. However, it’s critically important that the seatpost should never be raised so far that it’s not clamped in securely. For that reason, the seatpost should have a minimum-insertion mark on the seatpost. If the seat cannot be raised adequately without exposing this mark, the frame is probably too small for you, and the safest solution is to get a bike with a bigger frame.

Other Parts

Mountain bikes often have suspension forks in the front and may have some other suspension mechanism built into the frame for the rear wheel. Other components that may be installed on some bikes include racks (called carriers in Britain) for carrying luggage; lights and reflectors to enable safe night riding; fenders (called mudguards in Britain) to fend off water and mud; cyclo computers to keep track of your speed and distance travelled; and warning devices to help you get noticed.

Except for suspension components, which usually are designed as integral parts of the bike, most of the other accessories listed here are mainly sold as aftermarket items.

Know Your Gruppos

These days, bikes are usually equipped with a gruppo (a set of components) rather than the grab-bag of components from different manufacturers that was quite typical in the days of the ten-speed and the early days of mountain biking. The particular gruppo installed says a lot about the quality of the bike. In this section, we’ll take a look at some of the gruppos found on bicycles and what they mean in terms of price and quality

Often a bike is not really equipped with a complete gruppo. Instead, the bicycle’s manufacturer or importer may have gone for the appeal of a higher-end gruppo but saved some money by substituting cheaper parts for the less obvious ones. This is often a good way to keep the price down. That does not necessarily result in an inferior bike. For example, some non-Shimano brakes and cranksets may be at least as good as Shimano’s equivalents offered as part of a certain gruppo. The rear derailleur is generally considered the telltale part of a gruppo, and it’s easy enough to put on a rear derailleur from a high-end gruppo, but many of the other components, such as front derailleur, crankset, brakes, pedals, and headset, may be from a lower-quality gruppo. That may fool you into thinking you’re getting the level of quality associated with the glamorous rear derailleur, when in fact you are not.

Mountain Bike Gruppos

Ever since the demise of SunTour in the early 1990s, it’s been almost all Shimano in mountain biking. Besides Shimano, SRAM and its subsidiary, Sachs, offer fine products as well. Here’s the Shimano mountain bike gruppo lineup from top to bottom.

XTR (precise and lightweight, found only on the most expensive bikes intended mainly for competition costing $1,500 or more)

Deore XT (excellent quality but some parts slightly heavier; installed mainly on high-end bikes costing $800 or more)

Deore LX (good quality but slightly heavier again; found on bikes costing $600 or more)

STX-RC (OK quality; found mainly on nice recreational-level bikes)

Alevio (recreational-level equipment with cantilever brakes instead of direct-pull brakes)

Acera, Altus, Tourney, CX, MJ (work fine when new but have adjustability and wear problems; MJ is sized for young teenagers)

Nexus, Nexave (designed for city bikes and utility bikes, works very well for the purpose and is mentioned at the end of this list only because it’s different, not because it’s cheaper than recreational-level mountain bike gruppos)

Road Bike Gruppos

In this category, Campagnolo is still a viable alternative to Shimano’s products. Other manufacturers, mainly Sachs and Mavic, are also factors here. Here are the lineups for Shimano and Campagnolo respectively, again listed from top to bottom.

Shimano Road Gruppos

Dura-Ace (Shimano’s finest; used for high-end competition bikes costing $1,500 or more)

Ultegra (slightly heavier and less polished, but excellent quality; used on bikes costing $800 or more)

105 SC (OK quality when new, but with more plastic and slightly more susceptible to wear and damage; used on bikes costing $600 or more)

RX 100, RSX, Exage 300 EX (work fine when new but have adjustability and wear problems)

Campagnolo Road Gruppos

Record (the choice of champions and others who can afford it, used on bikes costing $1,500 or more)

Chorus (almost as nice but less titanium—at a substantial savings; used on bikes costing $1,000 or more)

Athena (good enough for most racing and long, fast riding; used on bikes costing $800 or more)

Veloce (in the same price category as Shimano’s 105 but nicer finish and more durable; used on bikes costing $600 or more)

Mirage, Avanti (good value for recreational-level road bikes)

Speed TH (special equipment for high-end triathlon bikes with 26-inch wheels; listed at the end of this list only because it’s different, while it fits in the same category as record equipment)



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