(The primary, more correct meaning of "pitch circle " is the circle running through the centers of the chain rollers of a chain engaged with the sprocket.)

I believe this was first used on Santana tandems.

Pacman Braze-on	Arai cable Quick-release

Contrary to popular belief, "pannier" is not a French word, and should not be pronounced as one. The normal English pronunciation is: "PAN-yer".

"Pannier" is, in fact derived from a French word: "panier", a basket (more specifically, a bread basket, from "pain", the French word for "bread."

A pantograph with an engraving tool is commonly used to engrave names in bicycle parts. High-end bikes, particularly Italian ones, sometimes have the frame builder's name "pantographed" on the handlebar stem, cranks/chainrings, lugs, etc.

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.

This type of linkage is also used in some V brakes to provide a more nearly horizontal motion to the brake shoe, and to keep the shoe angle constant.

To be eligible to ride in major randonnées, a rider must qualify by riding a series of shorter randonnées called "brevets.". This is widely considered the most challenging non-racing event in cycling.

• Paris Brest Paris official site
• Harriet Fell, 1975 PBP
• Emily O'Brien, 2007 PBP

The name derives from the fact that racers on a tight budget would often have to make due with peanut-butter sandwiches while on the road, and in the abscense of kitchen facilities, they would use the handle of this wrench to spread the peanut butter on their bread.

Pedal Threading

Direction

The right pedal has a normal thread, but the left pedal has a left (reverse) thread.

The reason for this is not obvious: The force from bearing friction would, in fact, tend to unscrew pedals threaded in this manner. The fact is, however, that it is not the bearing friction that makes pedals unscrew themselves, but a phenomenon called "precession".

You can demonstrate this to yourself by performing a simple experiment. Hold a pencil loosely in one fist, and move the end of it in a circle. You will see that the pencil, as it rubs against the inside of your fist, rotates in the opposite direction.

Ignorant people outside the bike industry sometimes make the astonishing discovery that the way it has been done for 100 years is "wrong." "Look at these fools, they go to the trouble of using a left thread on one pedal, then the bozos go and put the left thread on the wrong side! Shows that bicycle designers have no idea what they are doing..."

Another popular theory of armchair engineers is that the threads are done this way so that, if the pedal bearing locks up, the pedal will unscrew itself instead of breaking the rider's ankle.

The left threaded left pedal was not the result of armchair theorizing, it was a solution to a real problem: people's left pedals kept unscrewing! I have read that this was invented by the Wright brothers, but I am not sure of this.

Note! The precession effect doesn't substitute for screwing your pedals in good and tight. It is very important to do so. The threads (like virtually all threads on a bicycle) should be lubricated with grease, or at least with oil.

Thread Sizes

• Most pedals have 9/16" x 20 tpi threads.

• Pedals for one-piece cranks are 1/2" x 20 tpi.

• Older French bicycles used a 14 mm x 1.25 mm thread, but these are quite rare.

• In the early 1980s, Shimano attempted to popularize a very large thread size, which they called "Dyna Drive." This system was designed to place the pedal bearing inside of the crank, so that the foot could be slightly below the pivot point of the pedal bearing. This was believed to offer biomechanical advantages, but the system was not a commercial success, and has been abandoned.

Pedal Types

• Plain pedals rely on the rider's coordination to keep the foot properly located on the pedal. This type of pedal is most popular with beginner or unsophisticated riders, who fear being unable to put a foot down in a hurry.

• Toe-clippable pedals (sometimes known as "rat trap" or "quill" pedals) which work with stirrup-like clips and adjustable straps to hold the foot in place. These were the near-universal choice of knowledgeable cyclists until the 1980's. Toe-clip pedals, especially "platform" pedals, may be used either with normal street shoes or with special cleated shoes. The use of cleated shoes with toe clips, however, was made obsolete by the development of:

• Clipless pedals, which provide a positive connection between the shoe and the pedal, without the constriction of straps.

Tandemists sometimes like to experiment with different phasing of the cranks. One alternative is "90 degrees out of phase", where one set of cranks is horizontal while the other is vertical. This produces a smoother power flow, although it is a debatable whether this matters. Out of phase cranks complicate high-speed cornering, since both riders cannot have their cranks horizontal at the same time.

Out-of-phase cranks disrupt the unity of a tandem team, since the two riders are not moving in the same direction at the same time. As Osman Isvan says:

"There are essentially three entities riding a tandem:
The captain, the stoker, and the spirit.
It is the spirit who likes in-phase cranks."

Some tandemists prefer a setup that is only slightly out-of-phase, typically with the pilot's chainwheel one or two teeth ahead of the stoker's.

See also my article on Tandem Synch Chains.

The company also supplies an excellent grease and oil.

The Phil Wood spoke machine is an all mechanical machine that cuts and threads spokes to any desired length in a single operation, by simply pulling a lever. This machine is in a class by itself.

Formerly, Phil Wood also made pedals and one of the first disc brakes ever designed for bicycles. These products were less successful than those mentioned above. The disc brake, in particular, is considered quite dangerous by some. They were prone to fracture of the disc, which would cause abrupt, total brake failure, with no warning. There are no parts available for the disc brakes. They were designed an asbestos-based disc, and the use of this material for brakes is no longer legal.

The major bicycle application for pillow blocks is for handlebar stems . Most decent-quality BMX bicycles use pillow-block type stems, and this is another term for what is known as a "pop-top" stem.

The bolt may fit through "ears" that are attached to the outside of the outer part, or it may close the gap of a split collar which surrounds the upper part of the seat tube.

A few older bicycles used a collar and pinch bolt to secure a handlebar stem inside of the steerer. This system is particularly common on folding bicycles to allow the use of a quick-release for the handlebar stem. This required a compression slot to be cut into the steerer, which could constitute a stress riser.

These pins and ramps help catch the chain to help it climb from a smaller to a larger chainring. The smallest chainring will usually not have these features, because you never upshift to the smallest ring.

Steel pins are used in aluminum chainrings for improved wear resistance. The pins do the actual lifting of the chain, and take the most stress. The ramps just provide a smooth path for the chain to climb once it has been lifted by the pins.

Hyperglide type rear sprockets have similar ramps, but don't need pins, because the sprockets are hardened steel.

These features help improve shifting, and make rider skill less important in shifting, but none of these features is actually essential to the functioning of any system.

Pinch flats (also known as "snakebites" because there are usually two small holes in the tube, as if made by the fangs of a snake) are usually caused by carelessness or riding under-inflated tires. They can also be caused by the use of a tire which is too narrow for the weight it is asked to carry.

If the tire is too soft, or too narrow, it is easy for it to bottom out when striking an obstruction.

If the tire is hard enough and plump enough to carry the weight, the air will keep the tube from being pinched between the rim and the road hazard.

In British usage, the term "Pitch Circle Diameter" ("PCD") is also sometimes used as a synonym for what is more properly called "Bolt Circle Diameter" ("BCD")

If the drive sprocket is connected to the gear ring, and the cage that holds the planet gears is used to turn the wheel, the wheel will turn slower than the sprocket, thus providing a lower gear, compared with a simple hub driven by the same size sprockets.

If the drive sprocket is connected to the planet cage, and the gear ring drives the wheel, the result is a higher gear. Most three-speed internally-geared hubs use these two configurations, along with the direct drive to provide the three speeds.

Internally-geared hubs with more than three speeds use multiple sun pinions and sometimes multiple planet gears in the same manner.

You could make a case that "planetary gearing" is the earliest use of space technology in vehicle design...

See also my articles on English 3-speeds and Sachs/Shimano 7-speed hubs.

Platform pedals have superior ground clearance to double-sided pedals, and provide easier, faster entry to the toe clip than other styles.

Pliers have very limited use for bicycle work, and many bicycle parts are damaged by incompetents who try to use pliers for a job that really calls for a wrench. This commonly results in damage to the surfaces of the nuts or bolts so abused, as the serrated jaws slip around.

Many accidents are caused by people attempting to secure axle nuts with pliers. This cannot be done by people of normal hand strength, the nuts will not be tight, and the wheel is liable to fall out. Never use pliers to tighten nuts or bolts!

Locking pliers, such as Vise-Grips ® can grip a nut or bolt hard enough, but will ruin the driving surface so that it will be unusable with the correct tool.

In general usage, "pneumatic" refers to any device which operates by air pressure.

Pop-top stems permit much easier stem removal/replacement, because they permit the handlebar to be detached from the stem without removal of grips, tape or brake/shift controls. Most newer bikes come with this type of stem.

Traditional aluminum stems are forged or cast, and the horizontal section is solid. The horizontal section is kept relatively thin to keep weight down, but as a result it's less stiff than might be desired.

With a pop-top stem, the manufacturer can use a considerably larger diameter for the horizontal section, and then bore out the middle for lightness. (With a traditional pinch-bolt type stem, there's no access to drill out the horizontal section.)

Most other indexing systems place the detents in the control lever.

See the 1982 Shimano Catalogue on this site.

As a result, some manufacturers have taken to adding devices that deliberately sabotage the functionality of the front brake, out of fear that an unskilled rider will take a header as a result of improper use of the front brake.

These sabotage devices are commonly called "power modulators" and sometimes are marketed as if they were a version of ABS braking as used on newer cars.

This is a very foolish approach, probably driven by the common superstition that the use of the front brake is inherently dangerous. The result is increased stopping distance. This is a "safety" feature that is actually more likely to be a detriment to safety.

See also my article on Braking and Turning

With a pure friction lever, the friction has to at least equal the maximum pull of the derailer spring. When these are close, it takes almost no effort to push the lever forward (loosening the cable and the spring,) because the spring is helping you push the lever forward.

However, when you pull backward on the lever, tightening the cable, you are working against both the resistance of the friction clutch in the shift lever and the spring tension.

This creates an asymmetry of lever force between upshifting and downshifting.

With a "Power Ratchet" system, the ratchet disengages the friction clutch as you pull the lever backward, so you're only working against the spring. This gives a notably nicer feel to the shifter.

Other brands have solved this problem different ways. Shimano used to use a spring in the shifter that opposed the derailer's spring. This avoided the slightly "granular" feel created by the ratchet.

The legendary Simplex "Retrofriction " levers did something similar, using a pawl-less ratchet. As a result the Simplex design didn't have the "micro clicks" of the Sun Tour design.

See the Pedals entry in this Glossary, and Jobst Brandt's article on Left Hand Threads on this site for a detailed explanation of precession.

• Bearings are commonly supplied with a slight pre-load, that is, they are made to be slightly tighter than would permit the freest possible motion. This is to prevent slop in the bearing, and to ensure that the stresses are shared by multiple balls or rollers.

• Some suspension parts, particularly suspension stems and seatposts are designed with an adjustable pre-load. This is adjusted so that in carrying the rider's steady-state weight, the part is pressed up against a stop, so that it doesn't bounce up and down with minor road irregularities or body movements. When a more serious bump is hit, the suspension will respond to the greater load thus applied.

Small changes in tire pressure can have major effects on the ride quality and performance of a bicycle. It is best to experiment with different pressures to find out what works best for your particular combination of tire width, weight and surface conditions.

Tire pressure is much more important than, for instance, frame material in determining how your bike will ride.

For details, see the article on Tires on this site.

See also the article on Flat Tires on this site.

Presta valves have built-in valve caps, which must be opened before you can pump them up. These caps are "captive" nuts, which cannot be removed. Since there is no spring in a Presta valve, this knurled nut must be retightened after inflating the tire, or the valve may leak slowly.

Presta valves are light, and don't require as large a hole in the rim. Since the don't use a spring, they can be easier to pump with a hand pump.

Separate valve caps are not needed with Presta valves. The caps that come with Presta tubes and tubulars are there so that the pointy end of the valve won't puncture your spare tube or tubular while it is rolled up. There's no reason to use them in actual riding

Presta valve closed	Presta valve open	Presta valve with adaptor

Schrader valve	Woods valve

In addition to the primary chain, a tandem will have one or more "timing" or "synch" chains, connecting the bottom brackets

• Crank pullers

• Freewheel pullers

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 (as on most SWB recumbents, where the front wheel gets in the way of a straight chain run.)

  • ...adjust the tension on a chain (as with tandem synch chains.)

  • ...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.