Bearing
A bearing is the point of contact between a turning part and a non-turning part. A good bearing assembly has little or no play, and as little friction as possible.
Bottom Bracket
The part of the frame around which the pedal cranks revolve, also the bearings and axle assembly that runs through the bottom bracket shell of the frame.
Cadence
The speed at which the pedals turn, measured in Revolutions Per Minute. Inexperienced cyclists tend to ride in higher gears than they should, pedaling at a slower cadence.
Most experienced cyclists pedal at cadences in the range of 70-90 RPM. This puts less strain on the joints, particularly the knees. Racing cyclists often use even higher cadences for bursts of accelleration.
Caliper Brake
A caliper is a measuring device with moving parts that come together to determine the dimensions of a part.
Most bicycle brakes use a similar mechanism to move the brake shoes inward toward the rim, so they are called caliper brakes. A caliper brake uses a single assembly to move both brake shoes together, unlike a cantilever brake which has a separate unit on each side of the rim.
A brake caliper attaches to the bicycle by a single bolt, through the center of the fork crown or the brake bridge on the seat stays.
Cantilever Brakes
A cantilever brake has two separate arms, or cantilevers, one on each side of the rim. Each arm has pivots on an independent boss, and the two arms are usually coordinated and linked by a transverse (or straddle or crossover) cable that runs above the top of the tire. The transverse cable is commonly connected to the main brake cable by a yoke. In some newer designs, the end of the main cable becomes half of the transverse cable, and a short link wire forms the other half. For details on cantilevers, see my article on Cantilever Geometry
A recent variation on cantilever brakes is the V brake which dispenses with the transverse cable altogether.
Center-to-Center
In measuring distances between round things, whether they're tubes or holes, the usual method is to measure the distance from the centers of the circles.
In the case of measuring bicycle frames, all measurements are assumed to be center-to-center except for the seat tube length.
Seat tubes are sometimes measured from the center of the bottom bracket, but the upper end point may vary depending on the measurement system choesn. Center-to-center seat tube measuremnents measure to the intersection of the center of the top tube with the center of the seat tube.
Center-Pull Brake
A caliper brake in which the main cable runs down the center line of the bicycle, using a yoke to connect to a transverse cable. Technically, a normal cantilever brake is a form of center-pull brake, but the term is normally used to refer to caliper brakes only. This type of brake was popular from the late 1960's to the early 1980's, but is currently out of fashion. Center-pull brakes are a good choice for bicycles that have a long reach from the mounting point to the rim.
Chain
Modern bicycles use 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 all modern bicycle chain). The width is the internal width where the sprocket teeth fit in. Bicycle chain 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 chain with thinner side plates and flush rivets.
Chainwheel
Popular term for a front sprocket.
Cleat
A leather, plastic or metal fitting attched to the bottom of a cycling shoe to provide positive engagement with the pedal.
Clipless Pedals
Up until the late '80s, the choice was between plain pedals or pedals with toe clips and straps. Since "clipless" pedals provided a way to have a secure attachment to the pedal without the use of toe clips, the name stuck, even though it is sometimes confusing to newcomers.
"Clipless" or "Step-in" pedals use a mechanism similar to a ski binding. In fact the first successful system was made by a ski binding manufacturer, Look. Clipless pedals use a cleat which is bolted to the bottom of the shoe. When the rider steps on the pedal with the cleat, the cleat locks into the pedals mechanism, and is held firmly in place. Some systems hold the foot at a fixed angle, others allow various amounts of "float", or angular rotation of the foot on the pedal.
With most clipless pedal systems, the foot is disengaged by twisting the heel outward. Some of the earlier systems, such as the pioneering Cinelli model, required the rider to reach down and operate a release mechanism by hand. This style is sometimes jocularly referred to as "death cleats."
Crank
The arm which connects the pedal to the bottom bracket axle. Sometimes called a "crank arm", but this is redundant and inelegant. Call it a crank, or call it an arm, but please don't call it a "crank arm"
Crown
The upper part of the front fork, where the blades and steerer attach together
Derailleur
A mechanism for moving the chain from one sprocket to another to change gears on a multi-speed bicycle.
Down Tube
The frame tube that runs diagonally up from the front of the bottom bracket up to the lower end of the head tube.
Fork
Usually refers to the front fork, the part of the frame set that holds the front wheel. The fork is attached to the main frame by the headset. The fork consists of the two blades that go down to hold the the axle, the fork crown, and the steerer.
Frame Set
Usually, a "frame set" will consist of the frame and fork. In some cases, it may also include a headset and/or a seat post, or other parts peculiar to the frame involved.
Frame Size
Frame size generally refers to a measurement of the seat tube. This is measured from the center of the bottom bracket to somewhere near the top of the seat tube. Unfortunately, manufacturers disagree about where to figure the top of the seat tube, so the same frame may have as many as 8 different size numbers attached to it, depending on the manufacturer!
- Frame size may be measured in inches or centimeters.
- Some manufacturers measure "center-to-center ", i.e. to the intersection of the center of the top tube with the seat tube.
- Some measure to the intersection of the top of the top tube.
- Some measure to the top of the seat tube (which protrudes a variable amount above the top tube.)
- Some measure, on bikes with a sloping top tube, to where the seat tube would end up if the top tube didn't slope!
- A further complication is that different bicycles have different-height bottom brackets, so the stand-over height of two different frames may differ, even though both are 58cm center-to-center!
If you ask a bike sales person "what size frame do I need", and get back a number as an answer, without specifying a particular make and model group, you are not getting good advice.
Gear
The "gear" of a bicycle relates to the mechanical advantage of the whole drive system. In a low gear, the pedals are easy to turn, but you have to spin very fast to get any speed up. In a high gear, the pedals are hard to turn, but you don't have to make them turn very fast to make the bicycle go fast.
The gear of a bicycle depends on the ratio between the sizes of the front and rear sprockets, and the size of the drive wheel.
Headset
The bearing assembly that connects the front fork to the frame, and permits the fork to turn for steering and balancing.
Head Tube
The front tube of the frame, through which the steerer passes. The length of the head tube gives a quick visual indication of frame size, because it varies more, proportionally, with frame size than any of the other tubes.
High (Gear)
A high gear is one in which the pedals move slowly compared to the speed of the wheels. High gears are achieved by using large chainwheels and small rear sprockets.
High gears are for going fast, when the terrain permits. The rider must push much harder on the pedals in a high gear, so high gears are not suitable for lower-speed riding, due to the great strain that hard, slow pedaling puts on the joints.
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, disc or roller brake. Some rear hubs also incorporate internal planetary gearing.
Idler
An idler is a pulley or roller that does not produce any mechanical advantage, nor transmit power to a shaft. Idlers are used to lead a chain around a bend, or to take up slack in a drive chain
Jockey Pulley
The upper pulley on a rear derailer. This is the pulley that actually guides the chain from one sprocket to another. Shimano jockey pulleys are designed with a "Centeron®" mechanism that allows a small amount of sidewards motion to compensate for imprecise index adjustment.
Low (Gear)
A low gear is one in which the pedals move rapidly compared to the speed of the wheels.
Low gears make the pedals easy to push, but you need to turn them faster to get the bike to move at a good speed.
Low gears are achieved by using small chainwheels and large rear sprockets.
Low gears are used for climbing hills, or for starting up from a stop.
Mechanical Advantage
Every linkage that transmits power has a particular mechanical advantage. This is a ratio between the amount of force applied and the amount delivered. "Work" is defined as a force applied through a distance. When work is transmitted through a mechanism that has a mechanical advantage other than 1:1, the force can be increased at the expense of acting throught a reduced distance (as in the case of bicycle brakes, or gear shift levers) or the distance can be increased at the expense of reducing the amount of force transmitted (as in the case of the chain drive where the driving sprocket is larger than the driven sprocket.)
Mountain Bike
"Mountain bike" (MTB) is the currently preferred term for bicycles made for off-road use. Mountain bikes use 559 mm wheels, have at least 15 speeds, and usually have cantilever brakes. There was an attempt to make a copyright out of "MountainBike", but the term has become generic. Some have tried to promote the term "All Terrain Bike" (ATB) as an alternative, or to designate some subtle variant of the mountain bike, but this term has largely fallen into disuse.
The mountain bike is in many ways a hybrid design, a cross between a BMX bicycle and a touring bicycle.
Paralellogram
A parallelogram is a four sided geometric form, in which opposite sides are of equal length. A rectangle is a paralellogram in which the angles are 90 degrees.
A parallelogram linkage with pivots at the four corners will allow the angles to change as it flexes, but the facing sides always remain parallel to one another. This is a very useful mechanism for derailers, because it allows the derailer cage to move sideways while remaining parallel to the chain, and without the friction that would result from a sliding motion, as used on older plunger-type derailers.
Pinch Bolt
When a round part is held inside another round part, but adjustability is desired, the outer part will often have a slot or gap. This gap will be bridged by a bolt that can squeeze or "pinch" the outer part so that it will clamp onto the inner part. Such a bolt is called a pinch bolt. Most bicycles use pinch bolts to secure the seatpost into the seat tube of the frame, and to secure the handlebars to the stem. Threadless stems usually use pinch bolts to secure the stem to the steerer.
Pulley
Bicycles use pulleys both for chains and for cables.
Chain pulleys
- Most rear derailers use two pulleys in a spring-loaded cage to regulate the tension of the chain as it runs over different sized sprockets. The upper pulley is called the "jockey" pulley, the lower one is the "tension" pulley.
- Idler pulleys are used to:
...lead a chain around an obstruction
...adjust the tension on a chain
...apply extra tension and guidance to prevent accidental derailment on downhill bicycles.
Cable pulleys
- Pulleys have traditionally been used on 3-speeds to lead the cable where it crosses the seat tube, either at the top (following the top tube/seat stay) or the bottom (following the down tube/chain stay) of the seat tube.
- Many early '90s mountain bikes used a pulley at the bottom of the seat tube, to permit top-pull cable routing with bottom-pull front derailers. Since top-pull front derailers became readily available, this system has been obsolete.
- Accessory cable pulleys, such as the Avid Rollamajig ® are sometimes used in place of the traditional loop of cable housing where the cable enters the rear derailer.
- Pulleys are also used on brake cables:
...for center-pull/cantilever rear brakes on ladys' bicycles, where the cable has to make a sharp bend after it runs up the back of the seat tube.
...in some mountain-bike handlebar stems, where the housing enters in line with the stem extension, and the bare cable runs around a roller toward the cantilever. (Some people believe that this is dangerous, due to potentially higher risk of breaking the cable due to repeated flexing of the cable.)
Eccentric pulleys are sometimes used to change the mechanical advantage of a cable. This is most commonly done to permit the use of direct-pull cantilevers with conventional levers.
Rim
The outer metal hoop of a bicycle wheel. The rim does not include the spokes, nor the hub.
Roller Chain
Standard bicycle chain has rollers that smooth the engagement of the chain with the sprockets.
Seat Cluster
The junction between the seat tube, the top tube and the seat stays of a frame. The seat cluster usually also incorporates the seat-post binder bolt that clamps the seat tube or seat lug tight around the seat post to secure it.
Seat Post
The tubular support that holds the seat. 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.
Seat Stays
The thin frame tubes that run from the rear fork ends up to the seat cluster.
Seat Tube
The frame tube running from the bottom bracket up to the seat cluster.
Serrated
Equipped with serrations ("teeth") to improve grip. Cone locknuts, washers, jaws of vise grips, pliers, pipe wrenches, saddle clamps.
Spoke
One of the wires connecting the rim to the hub of a bicycle wheel.
Sprocket
A toothed wheel or gear that is part of a chain drive.
Steerer
The steerer, or "steering column" is the upper part of a front fork, to which the handlebar stem and the turning parts of the headset attach. The steerer is not visible on an assembled bicycle, being entirely concealed inside the head tube.
Stem
The part that connects the handlebars to the steerer of the fork.
Tension Pulley
The lower pulley on a rear derailer. So called because its main function is to adjust the tension on the chain as different-sized sprockets are selected.
Toe Clips
Toe Clips are stirrup-like devices that attach to pedals. They are normally used with leather or fabric straps. Actually, the straps are more important than the clips, but without the clips it is nearly impossible to get into the straps, because the clips hold the straps open, allowing the rider to slip into them.
Top Tube
The frame tube that runs horizontally from the top of the head tube to the seat cluster. Up until the 1980's, most high quality bicycles were built with the top tube exactly horizontal. Newer frame designs commonly have sloping top tubes, higher at the front. This is particularly common in smaller frame sizes.
Transverse Cable
The horizontal cable linking the two arms of a cantilever or center-pull brake. Also called a "straddle" or "crossover" cable.
Yoke
A fitting used on center-pull caliper and cantilever brakes which use a transverse cable. The yoke is the part that connects the main cable to the transverse cable. |