Frame Frames are structured of tubes of metal which support all of the bike and rider. Before the 1980's, all frames were made of steel, but nowadays lighter alloys of aluminum or titanium and even carbon fiber have become available. All operational parts and assemblies are attached to the frame. Fork Attaches the steering system (handlebars and stem), to the front wheel. Crank Set The two-armed mechanism that connects the pedals to the front chainring. Bottom Bracket Can refer to either the short threaded tube that runs perpendicular to the rest of the frame tubes where the cranks attach, or the actual set of spindle and bearings that threads into the frame. Pedals The part of the bike you put your foot on. The axles of the pedals screw into the cranks. Shifter The hand control for a gear shifting system. Most shifters use either a handlebar grip or a thumb shifter as the mechanism. Chain Bicycles use a roller chain to connect the cranks to the rear wheel. Chain drives are among the most efficient means of power transmission known. Chain size is specified by pitch and width. The pitch is the distance between rollers (1/2" on most bicycle chains). The width is the internal width where the sprocket teeth fit in. Bicycle chains comes in two basic widths: 1/8" chain is used on most single-speed bicycles, and bicycles with internal gearing. 3/32" chain is used on derailer equipped bicycles that have more than 3 speeds. Chains for derailer applications also come in various external widths. Newer clusters which have more sprockets use chains with thinner side plates and flush rivets. Rims The outer metal hoop of a bicycle wheel. The rim does not include the spokes, nor the hub. Tires A tire is made up of three parts: The beads are two hoops of strong steel wire (or, sometimes Kevlar®.) The cords, cloth forming the body of the tire, woven between the two beads. Most modern tires use nylon cords. The rubber, which covers all the other parts. The rubber on the part that contacts the road is thicker, and is called the tread. Most bicycle tires are not airtight by themselves, so they use an inner tube, which is basically a doughnut-shaped rubber balloon. The inner tube has a valve to allow you to blow it up. Some newer bicycles use tubeless tires, which are similar to a car tire, where no inner tube is needed to keep the tire inflated. These tires are relatively new to the biking world, tubeless tires can reduce the number of flats experienced due to hitting a hard object that may pinch and puncture an innertube. Front and Rear Hub The middle part of a wheel, to which the inside ends of the spokes attach. Consists of an axle, which attaches to the fork ends; a shell, to which the spokes attach, and bearings to connect the axle to the shell, permitting the shell to revolve around the axle. In the case of a rear hub, the shell would also have a provision for attaching the rear sprocket(s). Some hubs incorporate a coaster, drum, disk or roller brake. Some rear hubs also incorporate internal planetary gearing. Spokes The wires connecting the rim to the hub of a bicycle wheel. A conventional spoke has a swaged head, like the head of a nail, to keep it from pulling through the flange of the hub. Immediately after the head the spoke takes a right-angle bend, also known as the "elbow" of the spoke. The outer end of the spoke is threaded, and a special nut called a nipple fits through the rim and screws onto the spoke threads. 32 spoke wheels are the most common. Manufacturers tout this as an advantage, because it saves a very small amount of weight. Traditionally, spoke diameters were specified in terms of wire gauge, but the trend is toward specifying the diameter in millimeters. Spoke length is measured from the inside of the elbow to the very end of the threads, most usually in millimeters. Front and Rear Brake On bicycles there are three types of braking systems: caliper brakes, coaster brakes, and disc brakes. Caliper brakes use a pair of calipers to grab the rim to stop the bike. Usually operated by a brake lever. Coaster brakes are a type of brake mechanism enclosed inside the rear hub and operated by stepping backwards on the pedals. Usually found on children's bikes. Disc brakes are generally found on more expensive bikes and provide greater stopping power. The disc system is similar in design to an automotive disc brake. Brake Levers The operating control for a brake system, usually found on the handlebar. Handle Bar Handle bars on early bicycles were actually bars of solid steel. Solid handlebars became obsolete before the end of the 19th century; all modern handle "bars" are actually tubular, but the name persists. Conventional handlebars are divided broadly into two styles: "drop" and "upright" A drop handlebar is one in which the middle of the bar is the highest point, or nearly. Most bicycles built for fast or long-distance riding have drop handlebars, which provide a range of different grip positions, allowing the rider to change positions for variety and to accommodate different road/wind conditions. Upright handlebars are used on most of the world's bicycles. They permit a fairly erect posture of the upper body, and are more comfortable for cyclists who ride at a low intensity level. Stem The part that connects the handlebars to the steerer of the fork. Types of stems: Conventional stems for most bicycles with threaded headsets fit inside the steerer of the fork, and use an expander/wedge to attach to the steerer. The stem diameter must match the inside diameter of the steerer, which is usually 1/8" smaller than the nominal headset size. "Threadless" type stems clamp on to the outside of the steerer, so they must match the outside diameter of the steerer, which is the same as the nominal headset size. Stoker stems for tandems are very similar to "threadless" type stems, except that they clamp on to the seat tube of the rider in front, rather than to a steerer. Pinch-bolt type stems are not in common use any more. They work with a fork that has a steerer with a slot cut into it, and a collar with a pinch bolt for quick release. These are most often seen on folding bicycles, because this design permits the use of a quick release. "Adjustable" stems have the handlebar clamp unit mounted on a moveable part, permitting setting different amounts of forward extension. Grips The material on the handlebar used to better hold onto the bike. Headset The headset is the pair of bearings and bearing races (races are things that bearings sit in) at each end of the head tube that allow the fork to steer the bicycle smoothly. Saddle Frequently called a "seat", a bicycle's saddle is not intended to support the rider's entire weight. Traditional saddles are made of leather stretched over a metal frame, hammock style. This type of saddle requires care and careful breaking in, but when this is done the classic leather saddle moulds itself to fit the particular anatomical shape of its rider. Leather saddles are particularly well suited to long-distance tourists, and have their greatest advantage in hot weather, because they are porous and able to breathe, unlike plastic saddles which have closed-cell foam (also known as "gel") as a cushion. Seat Post The tubular support that holds the saddle. The seat post telescopes into the seat tube of the frame, providing the adjustment for saddle height. It is usually secured by a pinch bolt at the top of th seat tube. Older seat posts, and those on less expensive bicycles, are basically pieces of pipe, perhaps with a different diameter (usually 7/8" / 22.2 mm) at the top end. A separate clamp attaches the saddle to this type of seat post. Modern, high-quality seat posts have the seat clamp mechanism built into the top of the post. This type is also commonly referred to as "microadjusting" because it permits a finer degree of adjustment of the saddle angle. Seat posts come in a wide range of diameters, from 21.15 mm to 31.8 mm. Low end department-store bicycles are typically 21.15 mm (13/16"). Most bicycles with one-piece cranks, including most BMX machines use this size. Bicycles with standard-size (1 1/8" / 28.6 mm o.d.) seat tubes usually use sizes between 25.4 (1") and 27.2 (1.07"). They typically come in sizes with even-numbered tenths of millimeters (26.0, 26.2, 26.4...). For standard-sized seat tubes, the larger the seat post the thinner the tube. Thus, a larger seat-post size is often an indicator of a lighter, fancier frame. Seat Clamp Attaches the saddle to the seat post.