As time went on, the Bicycle Glossary has grown, and many of the pages became inconveniently large.I have split the larger pages into smaller ones, but I realize that there may be external links pointing to the older pages. For this reason, I have maintained copies of the older pages at the same location.
This is one of the older pages, and the newer pages that were derived from it are liable to be more complete and up to date, so please follow the links below to the current version. Sorry for any inconvenience.
If one of my own pages had a link that took you to this page, it would be helpful if you would send me an email with the URL of the page that had the bad link, so I can update it.
Sheldon Brown
This does not pretend to be an objective document.
All 42s are "A"s; All 39s are "B"s by definition.
There are two kinds of 53s:
If you have poor shifting skills, matching the chainrings by the letters will give slightly better shifting, but if you're a reasonably skilled cyclist, it really doesn't matter.
The bearings of a cup-and-cone bottom bracket are adjusted by screwing the adjustable cup in or out of the bottom bracket shell, and the adjustment is secured by the lock ring.
See also the Bottom Bracket Glossary Entry and my Tool Tips article on Bottom Bracket Adjustment.
Probably the oldest "ærodynamic" part is the drop handlebar. Many other bicycle parts are available in "æro" versions, including:
Æro bars make possible a significant improvement in speed, but with less secure control of the bicycle. They also eliminate most of the shock absorbency normally provided by the cyclist's bent elbows, so they are not suitable for rough surfaces. They are not usually allowed in mass-start racing.
Æro bars originated from an attempt to duplicate the "tuck" of a downhill skiier. They first appeared in 1986 when Pete Penseyres introduced them in the Race Across America (RAAM).
Although they were an instant hit with triathletes and time-trialists, professional racers were slow to accept this innovation. When Greg Lemond rode Scott æro clip-ons to victory in the decisive final time trial of the 1989 Tour de France, the ice was broken, and few racers will now ride time-trial stages without them.
Although æro bars originated as racing equipment, and are particularly associated with triathlons, they have also become quite popular with touring cyclists and randonneurs, as much for the relief that they give to the hands and wrists as for their ærodynamic qualities.
Æro levers are generally an improvement over the older type. The pivots are located differently, making it possible to get fairly serious braking from the position where the rider's hand is on top of the lever hood. Non-æro levers would permit the use of this position for gentle deceleration only.
Æro brake levers usually have more mechanical advantage, which is good in general, but may cause problems when they are used with cantilever or drum brakes that require more cable than conventional calipers.
In France, exposed brake cables remained popular longer than elsewhere, because French cylcists sometimes like to transport baguettes home from the boulangerie by resting them crosswise across the brake hoods. The cables help hold the loaves in position.
Airless tires have been obsolete for over a century, but crackpot "inventors" keep trying to bring them back. They are heavy and slow. They give a harsh ride and poor high-speed cornering on rough surfaces. They are also likely to cause wheel damage, due to their poor cushioning ability. A pneumatic tire uses all of the air in the whole tube as a shock absorber, while foam-type "airless" tires/tubes only use the air in the immediate area of impact.
Airless tires are either made of elastomers (rubbery materials) or closed cell foams, which are rubbery materials with lots of tiny air bubbles. The better ones are foam type, becausle solid elastomers have hardly any shockabsorbency.
This sort of material has a non-linear response to compression loads: as apply a compressive load, the stiffness of the material increases as it gets squashed thinner and thinner. The beauty of pneumatic tires is that the compression is nearly linear.
A basic fact of physics is that pressure is inversely proportional to volume.
Imagine a pneumatic tire that is divided into lots of little segments so that each inch or so of tire is effectively a separate "balloon." Let's say it's 1 inch thick, and when a rider sits on the bike, the tire compresses 1/4 inch. That means the volume of the localized "baloon" is now 75% of what it was before the rider got on, so the pressure in the bubble is going to become 133% of what it was.
If the rider hits a bump that compresses the tire another 1/4 inch, the volume will be half the static value, so the pressure will be double the starting pressure.
If the rider hits a bump that compresses the tire 1/2 inch (plus the static 1/4 inch) the volume will have been reduced to 25% of the base volume, and the pressure will now be 4 times the base pressure!
"Airless" tires that use foam derive their resiliency from the bubbles in the foam, so this describes their general functioning. The bubbles are only part of the mix, though, so a 1 inch thick tire doesn't actually have an inch of air to play with before the bubbles are all compressed as far as they can go. You can only compress the bubbles so much, and the more you compress them, the harder they press back, in geometric progression.
Contrast this with a pneumatic tire, where the whole volume of air in the tire is being compressed as a unit. When you sit on the bike, the bottom part of the tire flattens out, say 1/4 inch, but this only reduces the total air volume by a fraction of a percent. Thus the pressure is nearly constant under all conditions, and the tire can be equally shock-absorbent for the full "travel" of its thickness.
It is this property of providing nearly linear response to external pressure that is the unique feature of pneumatic tires, and it is not possible for any system that doesn't have this feature to give as good ride as pneumatics do. This is why every vehicle designed for road use in the last hundred years has used pneumatic tires.
The near-linear response of pneumatic tires is not just a matter of comfort. It also improves traction at higher speeds, because they don't tend to bounce as much as harder tires do. Bouncing can cause loss of traction in high speed corners, because when the tire is airborne, it can't have any traction.
Airless tires do have their applications. They can work well either where speeds are very slow, or where surfaces are very smooth. Thus, they're pretty satisfactory for wheelchairs, especially those mainly used indoors, and also for railroad trains, roller skates, furniture casters, children's riding toys and wagons.
This tool is sometimes confusingly called a "hex wrench," "Allen key" or "hex key."
The terms involving "hex" can be confusing, because normal cap screws also commonly have (male) hexagonal heads, and hexagonal box or socket wrenches fit them.
I prefer not to use the term "key" for such a tool. Many languages use the same word for "wrench" and "key", but I believe that it is one of the richnesses of the American English language that it makes this distinction. Since "wrench" is not used in this context in British usage, "Allen key" is acceptable if the appropriate accent is used.
One of the nice things about Allen wrenches is that they can be sharpened very easily, just grind the worn part off with a bench grinder, and an old tired Allen wrench becomes as good as new, so long as you don't let it get too hot while you are grinding it.
In common bicycle usage, "alloy" is usually a synonym for aluminum.
For instance, my 1957 OTB came with a 14/16/19/26 freewheel. The 14/16/19 gave a pretty good cruising range with the 48 tooth chainwheel, the 26 was for climbing hills (there was also a 30 tooth chainwheel for climbing serious hills).
Sometime in the early '70's, advertisers co-opted the term "alpine" and started to apply it to the 40/52-14//28 setups common on mass-produced 10-speeds of the '70's bike boom. As a result, the term became essentially meaningless.
On virtually all good quality bicycles, aluminum is used for cranks, chainwheels, rims, handlebars, stems, brake parts and derailer parts.
Aluminum is not suitable for spokes, cables, or highly stressed threaded fasteners in general.
In most English speaking countries outside of North America, they stick an extra syllable into the word, and call it "aluminium".
See also the excellent article by Scott Nicol on the Velo-News Tech Site.
Different aluminum alloys and treatments are designated by a numerical code, as explained by Jeff Del Papa:
The first digit tells what "family" it belongs to:
If you see things like -T6, following the alloy series, those describe
any heat treating the stuff got after it was made. Getting this done
correctly, is critical to the strength of the frame. For most
aluminum frames, it is done after the frame is welded, as the heat
from the welder will change the metal (usually makes aluminum alloys
softer) Heat treating typically involves heating to near melting
(900-1000F, it melts around 1100F, your oven self cleans at 800-850),
holding it there for some amount of time (for thin tube, 1/2-2 hours or
so) cooling suddenly (dunk in water), then a long bake (8 or more
hours) at a lower temprature (like 350F).
The different alloys vary in tensile strength, corrosion resistance,
welding compatibility, ductility, and machineability. The density of
aluminum alloys don't vary much at all (under 5%) and the stiffness,
doesn't change.
Each alloy has good points, and bad points. What counts as good, and
what is bad depends on what you are going to do with it. Some very
strong alloys can't be welded, so they make bad frames, and great
chainrings. Another might give up some absolute strength, but gain
some resistance to cracking. One may cost more, but the heat treating
process is cheaper. If you are bolting or bonding things together,
you can mix alloys. If you are going to weld, all the welded parts
have to use identical filler material, and heat treating schedule.
(so you can't mix 6061, and 7005 in the same welded structure)
It's the designers job to chose correctly amoung the various tradeoffs.
If the desinger chose well, even a not particularly exotic material
can do the job just fine. Pick wrong, and even exotic super-alloys
will break.
In general, bicycles with shallower, "slack", "relaxed" angles (lower numbers) tend to be more stable and comfortable. Bicycles with steeper, more upright angles (higher numbers) tend to be manuverable, but less comfortable on rough surfaces. Shallower frames tend to have longer wheel bases than more upright frames; bicycles with shallower head angles normally have more fork rake. All of these factors contribute to the riding characteristics cited.
This practice is pretty much discredited these days. If carried to an extreme, it can cause injury. This happened to me when I was a teen-ager; I had read about ankling, and had just acquired my first pair of toe clips, just before setting out on my first overnight tour. I ankled for about the first 30-40 miles, when there was a sudden sharp pain in one of my Achilles tendons. I had to lower the saddle, remove the toe clips, and finish out the 4 day tour pedaling on my arches, because I couldn't bear the slightest load on the front of my foot, pulling on the Achilles tendons. For about a month thereafter, I would need to massage my Achilles tendons for about 5 minutes each morning before I would be able to walk. 40 years later, I've still not completely recovered from this injury.
Some rims are "hard" anodized, which produces a hard surface, harder than the natural aluminum, usually in a dark brown or black. This process was popular in the 1980s, as it was presumed to improve the durability of the rim's braking surface, and to make the rim more resistant to cracking around the spoke holes.
Unfortunately, the anodized braking surfaces did not provide as good a grip as natural aluminum, and they presented an unsightly appearance as the dark coating wore off of the sides of the rim.
Even more unfortunately, it developed that the harder surface was also more brittle, causing more problems with cracking around the spoke holes.
The term "brake arch" does legitimately apply to the part of a suspension fork that links the sliders and contains the cable housing stop.
It uses a standard derailer operated by a system of weights and springs in the rear wheel.
As the speed increases, the weights move outward due to "centrifugal force", pushing a ring that rubs on the derailer outward, causing the derailer to shift to a higher gear.
There is no provision for the rider to have any control over the gear shifting.
Avocet is best known for cyclecomputers, tires and saddles.
The Avocet 20 cyclecomputer was the first to sell for less than $40. Unfortunately, it was widely advertised, with a price of $24.95, for almost two years before it was actually ready to ship. This "vaporware" did great harm to the developement of the cyclecomputer market for a couple of years. Avocet cyclcomputers work on an entirley different principle from all other makes.
Avocet was the first to market tires with perfectly smooth tread for road use. They are extremely good, but it is hard to convince people that they get good traction (they do!)
Avocet's first claim to fame was its saddles, which were the first serious alternative to traditional leather saddles. They were the first to use the "two-bump" design to reduce pressure on the perineum.
Avocet also used to market hubs and cranks made by Ofmega in Italy.
The name "Avocet" is pronounced "A-vo-cette". Despite appearances, it is an English word, not French, and refers to a particular shorebird species.
Acera-X
Acorn nut
Adaptor claw
A claw-shaped metal stamping for attaching a rear derailer to a frame that does not have a built-in derailer hanger. It is secured to the dropout by a small bolt with a special-shaped nut that fits in the back of the dropout's axle slot, and also by the rear axle nut or quick release skewer.
Adjusting barrel
A hollow bolt, designed so that a gear or brake cable can run down through the center of it, but the housing stops inside the head of the barrel. This allows fine adjustment of cable tension without requiring the use of any tools. Adjusting barrels may be located at the end of any run of cable housing. On brakes, their primary function is to permit easy adjustment to take up the slack as the brake shoes wear down. On gear shifting cables, they help fine tune the indexing.
Adjustable Cup
Ærial
Ærodynamic
Æro Bars
Æro brake levers
Aftermarket
Aheadset ®
Airless Tires
Alignment
Alivio
Allen Wrench
Alloy
All Rounder
Alpine gearing
Aluminum
They indicate what other stuff is mixed in with the aluminum. Pure
aluminum isn't all that strong. Add some silcon, magneisum, zinc,
copper, and other things, and the result will be far stronger.
1xxx Commercial aluminium (more than 99 per cent Al)
2xxx Copper
3xxx Manganese
4xxx Silicon
5xxx Magnesium
6xxx Magnesiun and silicon
7xxx Zinc
8xxx Other elements
Anatomic
Anchor bolt
Angles
Ankling
Anodized, anodizing
Arch (brake)
ASS
ATB
Ashtabula ® crank
Audax
Autobike ®
Autoshifting
Avocet ®
Axle
Axle set
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