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Bicycle Glossary Sa - So

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-- Sheldon (d. 2008), Harriet, John.
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Sachs was a European conglomerate that bought up many of the formerly independent French parts makers, including Atom/Maillard/Normandy (hubs, pedals, freewheels) Huret (derailers) and Sedis (chains.)

Sachs also made multi-speed internal-gear hubs in 3-, 5-, 7- and 12-speed versions. Their "3 x 7" hub was a hybrid system, a 3-speed internal hub that took a 7-sprocket cassette, providing 21 speeds with only one chainwheel.

Sachs formerly also made kick-back hubs and a "2 x 6" hybrid hub, the "Orbit". The one clear area of domination for Sachs was its chains, which were generally acknowledged to be the finest available.

Sachs was the major European competitor to Shimano for the general bicycle parts market. Their parts in general were quite good, and stand up well in comparison with Shimano equivalents, although exchange rate problems sometimes make them less affordable. The bicycle division was sold to the SRAM Corporation, in November 1997. Most of the products formerly called "Sachs" are now called "SRAM." Up-to-date information is on the SRAM site.

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 molds 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. There is a more extensive article on Leather Saddles on this site.

Most cyclists have never experienced the comfort of a well broken-in leather saddle, because most modern bicycles come with plastic saddles which require no break in or other maintenance. Plastic saddles are also lighter and cheaper than leather ones. There is a general, major article on saddles on this site, covering: Adjustment, Angle, Front/Back, Gel, Hard or Soft?, Height, Impotency, Leather, Pads, Plastic, Posting, Prostate, Recumbents, Springs, Seatposts, Suspension, Wide or Narrow?

A touring bag, which is attached to the rear of a bicycle saddle. "Touring bag" is less confusing, because the saddlebags used on a horse look much like bicycle pannier bags, which sit to either side of a bicycle wheel.
Society of Automotive Engineers, a quasi-official trade association which establishes standards for materials and parts used in the automotive industry. This body has jurisdiction over screw threads and wrench sizes based on the inch system, so inch-based fasteners are sometimes referred to as S.A.E. sizes.
Safety Bicycle
A conventional bicycle, with wheels of similar size and chain drive. When the modern style of bicycle was replacing the high wheeler, in the late 1880's, the new style was mainly noted for its greater safety compared to the older design.

The two breakthroughs that allowed the safety bicycle to obsolete the high wheeler were Dunlop's pneumatic tire and chain drive.

Safety Levers
Extension levers.
Sag Wagon
A car or truck that picks up or otherwise assists riders who have had to stop riding due to fatigue, injury, or mechanical failure. This is primarily a touring term, racers call the corresponding vehicle the "broom wagon."

Some people believe that the term derives from the verb "sag", others maintain that it is an acronym for "Support And Gear."

Santana ®
Santana is the world's leading manufacturer of high-end tandems. Starting in the late 1970s under the leadership of Bill McCready, Santana virtually re-invented the tandem, which had been in decline since the Second World War. Before Santana came onto the scene, there had been low-quality nass-produced American tandems, mediocre mass-produced French ones and a few high-grade custom ones from English and European makers. Santana undertook a major rethinking of tandem design. A major contribution was to discard the idea that a tandem should be as much like a solo bike as possible, with a short wheelbase for good handling. By increasing the room for the stoker, Santana made the tandem much more pleasant to ride. Also, Santana placed a premium on torsional frame stiffness, which is heavily tested in a tandem, and pioneered in assembling top-quality components and sourcing special items such as 48-spoke hubs and rims that made for reliable wheels.

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Standard automotive-style air valve. The other, skinny kind is called "Presta".

There is a third type of valve, very rarely seen in the U.S., which has a bottom similar to a Schrader and necks down to about the size of a Presta. This is a Woods valve, formerly popular in the British Isles and Asia.

Schrader Presta Woods
Schrader valve Presta valve Woods valve
If you want to convert a rim drilled for Presta valves to accept Schrader valves, drill it out with a 21/64" drill bit.

The external threaded part of a Schrader valve is 7.7 mm (.302") x 32 T.P.I.

A colloquial term for free samples of parts, clothing, etc. provided to bike-shop employees, usually at manufacturers' clinics or trade shows.

This term probably originated as a comical mispronunciation of "swag."

A fastener with male threads, usually with a slotted or recessed head. Strictly speaking, it's only a screw if the threads extend the full length of the shaft.

If the threads do not extend full length, technically it is a "bolt" but only pedants insist on this distinction.

Sealed bearingsbearing types
A "sealed" bearing is one which has rubber or plastic gaskets to prevent the entry of dirt. In the bicycle industry, the term "sealed bearing" is often used colloquially to refer to a cartridge bearing. This can be confusing to a consumer who may think that a hub is a high-tech cartridge-bearing unit, when it is actually a normal cup-and-cone bearing with a plastic dustcap.
The chair-like fitting the rider of a recumbent sits on; also a device for carrying small children on a bicycle. See also "saddle."
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 seatpost binder bolt that clamps the seat tube or seat lug tight around the seat post to secure it.
Metal tubing used in bicycle frames can be manufactured in two different ways:
Seat Lug
The lug at the seat cluster of a lugged frame.
Seat Pin
British term for seat post, particularly the simple "pipe" type seat post which uses a separate saddle clamp.
Seat Pillar
British term for seat post
The tubular support that holds the saddle. The seatpost 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 the seat tube.

Older seatposts, and those on cheap 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 seatpost.

Modern, high-quality seatposts have the saddle 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 have seatposts between 25.4 (1") and 27.2 (1.07") in diameter. Seatposts 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 seatpost size is often an indicator of a lighter, fancier frame.

I have a Database of Seat Post Sizes for various bicycles available on this site.

More information on seatposts is available in my article on Saddles.

Seatpost Bolt
The binder bolt that secures the seatpost in the frame. It may be a conventional bolt with a nut, or an Allen bolt, or a quick release.
Seat Mast
Seat post, or in the case of a Bike Friday folding bicycle, the upper part of the seat tube, which is hinged and folds down.
Seat Sandwich ®
An adaptor to allow a saddle with four frame rails to mount onto a standard one-bolt "microadjust" type seat post.

The adaptor consists of a grooved brass plate which fits between the upper and lower rails, so that the vertical clamp bolt doesn't distort them by squeezing them together. This accessory includes a longer than normal bolt, and is primarily used for mounting wider Brooks leather saddles, such as the B-72 and B-66.

The thin frame tubes that run from the rear forkends up to the seat cluster.
Seat Tube
The frame tube running from the bottom bracket up to the seat cluster. See also Seat Mast.
Selecta ®
Selecta was an early Shimano ® attempt at a splined crank/bottom bracket system, dating from the late '70s or early '80s.

The spline pattern was chosen to permit the spindle to fit through a Front-Freewheel bearing set, because a standard-sized square-tapered bottom bracket spindle would not fit.

This design turned out to be rather unreliable, due to the small diameter of the splines, and Shimano abandoned the system. Shimano did continue to supply spare parts for many years thereafter, but these are no longer available.

See the 1982 Shimano Catalogue on this site.

Self-energizing Brakes
Self-energizing brakes use some of the braking force to provide a "power assist" to the brakes. The best-known self-energizing brake is the Scott-Peterson (Sun Tour)cantilever, which has a steep, helical thread as its pivot, so that the forward force exerted by the rim against the pads helps cause the pads to press harder than they would from hand effort alone.

Self-energizing brakes are quite controversial, because they can have a non-linear response, which may lead to wheel lock-up.

"Selle" is Italian for "saddles." It is the plural of "sella," saddle.

There are several Italian saddle makers whose corporate name begins with "Selle", including Selle Italia, Selle Royal, Selle San Marco and others. Sometimes people try to shorten these names and say "Selle saddle", which actually makes no sense.

The most common spoke pattern, used on the vast majority of bicycles. See my wheelbuilding article.
Equipped with serrations ("teeth", from the Latin word for "saw" ) to improve grip. Cone locknuts, washers, jaws of vise grips, pliers, pipe wrenches, saddle clamps are serrated.
Italian for "silk". The finest tubular tires are made using silk fabric.

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Set Screw
A screw or bolt threaded into a ring or collar, designed to press against the shaft that the collar surrounds, so that the ring is held solidly against the shaft.

Rings with set screws are used to hold some cartridge bearing hubs and bottom bracket assemblies together.

Some tandem eccentric bottom brackets use set screws to hold the eccentric in position. A very few (mostly antique) bicycles also use set screws to secure the seatpost in the frame.

Tubular tire.
Small flange (hub)
Superglide ®
Shaft drive
An alternative drive system, replacing the chain and sprockets with right-angle bevel gears and a shaft running inside the right hand "chainstay."

Shaft drive was briefly popular around 1900, and occasional attempts are made to revive the design. Unfortunately, shaft drive turns out to have more problems than advantages.

A shaft drive requires heavier frame construction around the bevel gears to maintain their precise alignment under load. The drive system is heavier and less efficient than a good chain drive.

For reasons of clearance, the bevel gears of a shaft drive bicycle must be considerably smaller than the typical sprockets used with a chain drive. The smaller size of the gears causes an increase in the stresses on the whole support system for the shaft. This problem is exacerbated because the stresses from the shaft drive are not perpendicular the triangulated structure of a bicycle frame, and so are not well-resisted. .

Most of the advantages touted by proponents of shaft drive are only advantages compared with open-chain, derailer gear systems. Many proponents of shaft drive use specious (if not dishonest) arguments "comparing" shaft drive systems with derailer gear systems. Any such comparisons are meaningless, it's like comparing apples and locomotives.

A valid comparison of shaft vs. chain drives can only be made if both bikes use the same type of gearing, whether single-speed or with an internal gear system.

These same advantages can be obtained with chain drive using a fully-enclosing chain case, as with old English roadsters and many current Dutch bikes.

Shaft drive proponents also often compare sealed, enclosed shaft drive systems with open, exposed chain drive systems. This is also a misleading comparison. All of the advantages claimed for shaft drive can be realized by the use of a chain case.

Shark Fin ®
Shimano trademark for a chainstay protector with a projection near the front that was intended to keep the chain from getting jammed up if it overshifted the small chainring. This projection was triangular and resembled a shark's dorsal fin, hence the name.

This product was made of black plastic, with a peel-and-stick backing and a zip tie to hold it to the chainstay.

Shark Tooth ®
During the late '80s when there was a fad for mounting U-brakes under the chainstays. Shimano's Shark Tooth was a small plastic part that mounted to the right hand U-brake boss as an anti-chain-suck device.
Sheldon fender nut
A brake bolt nut for recessed brake mounting and which is extended and threaded all the way through so a bolt can be inserted from the outer end to support a fender. The term has become generic.

Conventional fender nut

Sheldon fender nut

conventional nut for recessed brake mounting Sheldon fender nut

The hand control for a gear shifting system. I used to object to this term, because it is actually the derailer or the internal hub that does the real shifting, and the part commonly called the "shifter" is only the control mechanism. I preferred the term "shift lever".

Because of the increased popularity of twist-grip type controls, which are not levers, I have reluctantly come to accept the common usage of the term "shifter" to refer to the hand control.

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The leading manufacturer of bicycle parts. Shimano has come to dominate the industry, and to have a near monopoly on many parts categories. Shimano gets a lot of bad press, being perceived as the Goliath of the industry.

Shimano achieved this position because it has the most successful research and development program in the industry. Shimano pioneered many key technologies:

Unfortunately, Shimano's pursuit of high performance has been somewhat at the expense of versatility. For example, to reap the benefits of Hyperglide or Superglide, you need to use one of the specific combinations of sprocket sizes designed to work together. While Shimano offers a pretty good selection, it doesn't have the perfect combination for every rider.

Shimano Date Codes:

Many Shimano parts feature a two-letter date code, indicating the year and month of manufacture. More information on specific Shimano models and technologies is on a separate Shimano Page. The date codes are explained here on the Vintage Trek site.
Shimmy is a term for a harmonic shaking of the bicycle, which usually occurs at a fairly high speed. Shimmy can be very scary, and can lead to loss of control.

All bicycles are subject to shimmy under the right (wrong) circumstances, but it is more pronounced in some than in others.

Also see our article on shimmy.

Sidepull Brake
A brake caliper that has one arm pulled by the inner cable, the other pushed by the cable housing. Usually, the cable runs down one side and both cable arms are on the same side of the caliper. Some sidepull brakes such as the Scott Superbrake, however, have both cable arms above the pivot, so the cable approaches from one side.
Silent Clutch
Shimano's term for a roller clutch
The finest tubular tires are made of silk fabric. Sometimes the term "silk" is used as a noun to refer to such tubulars.
Defunct French component manufacturer, one of the earliest makers of derailers. They are best known in the U.S. for the cheap plastic derailers supplied on millions of Bike Boom ten speeds.

Simplex also made a "Rétrofriction " down-tube shift lever that is considered by many to be the finest pre-index shift lever ever.

See also my page on French bicycles.

Single-groove Handlebars
Many newer drop handlebars have an indented groove or grooves in the curved section above the brake levers.
The traditional type of side-pull brake caliper The same bolt that holds the caliper to the frame acts as the pivot for the brake arms.
While any bike that doesn't have multiple gears is technically a "single-speed" bike, current use of the joined word "singlespeed" generally refers to a bike with a one-speed freewheel and hand brakes, distinct from both one-speed cruisers (these have coaster brakes, not freewheels) and fixed-gear machines.

See my Article on Singlespeed Mountain Bikes

(As far as I know, I was the first to deliberately remove the multiple-speed gearing from a mountain bike to make it simpler, lighter and more reliable...if I do say so myself!)

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A trail, such as a hiking trail, consisting of a single rut or path; this is as distinct from doubletrack, which refers to dirt roads or other routes made by and accessible to four-wheel vehicles.
Single Tube
An obsolete type of tubeless tire. Similar to a tubular, but made like a loop of garden hose. They were held on to wooden rims by shellac. This type of tire was obsolete by the end of the 1920's. The most common size was 28 x 1 1/2. A flat could only be repaired by inserting a plug from the outside; damage to the fabric required professional repair in a bicycle shop.

The rim diameter is about the same as standard tubulars , though few tubulars are as wide as the typical single tube. Reportedly, however, tubulars can be mounted on singletube rims. I haven't actually tried it, can't guarantee that it will work.

Single-tube tires were forced on the U.S. market by a monopoly that excluded the better European clincher tires. Because single-tube tires were so difficult to repair, they drastically reduced the appeal of bicycling in the USA -- as is clear from a comparison of levels of bicycle use in the USA and Canada, where good European tires were available.

See article by Paul Rubenson.

Siping is the use of narrow grooves in the tread of a tire. The purpose of this is to allow water to escape instead of being trapped between the tire and the road, causing "hydroplaning."

Bicycle tires have such a small contact patch and run at such high pressures that hydroplaning is an imaginary problem, even with completely slick tires.

Shimano Indexing System ®.
Ski Bend
A fairly long style of bar end, with a bend halfway along it causing the front part to bend inward and a bit upward.
Skid Patch

Fixed-gear riders who make a habit of doing "skip stops" wear the rear tire out considerably faster than those who use a brake. This problem is exacerbated by certain gear ratios, because they may tend to repeatedly skid on the same section of the tire.

Riders who plan to do a lot of skip stops should consider the ratio when selecting their chainring and rear sprocket. The mathematics of this is actually fairly simple:


48/12 simplifies to 4/1, so there will be only 1 skid patch

45/15 simplifies to 3/1 so there will only be 1 skid patch, or 2 if you are an ambidextrous skidder.

42/15 simplifies to 14/5, so there will be 5 skid patches.

44/16 simplifies to 11/4, so there will be 4 skid patches, or 8 if you are an ambidextrous skidder.

43/15 can't be further simplified, so there will be 15 skid patches, or 30 if you are an ambidextrous skidder.

Explanation: let's look at 45/15, or 3/1. The rear wheel turns exactly 3 times for each turn of the cranks -- so, if the same foot is forward, the same place on the rear tire is always down. 1/2 turn of the cranks places the other foot forward, and turns the rear wheel 1 1/2 times. Then, the opposite place on the tire is down. Similarly for higher numbers, if the numerator of the reduced fraction is even, skid patches will be in the same places with either crank forward, but if the numerator is odd, the number of skid patches with each crank forward will be odd, and skid patches with one crank forward will interleave with those with the other crank forward. John Allen's Excel spreadsheet calculates the number of skid patches for any sprocket combination.

A rear brake also leaves skid patches. The front wheel does not skid in normal braking. A front brake also can stop the bicycle much shorter, but requires care in use to avoid pitching the rider forward: see my article on braking and turning.

Skinwall Tire
A tire in which the cord of the sidewalls is only covered with a very thin coat of rubber, if any. This makes the tire more flexible, for lower rolling resistance, but the sidewalls are more easily damaged than those of blackwalls or gumwalls.
Skip Link
Older style of chain, with 1" pitch. This type of chain has the same number of rollers as a similar length of normal 1/2" pitch chain, but they are spaced alternately close together and far apart. Every other roller engages a sprocket tooth. This type of chain was in common use up until around World War II. See also block chain.

8 equals 16

An 8-tooth sprocket for 1" pitch "skip link" chain (left) is equivalent to a 16 for standard 1/2" chain.

Skip Stop
Fixed-gear riders generally need to master a technique called the "skip stop." This is a way that you can actually lock up the rear wheel using your legs alone. Since sliding friction is less than sticking friction, once the tire starts to skid, you will generally be able to maintain the skid until you've stopped or at least slowed down as much as you want to.

You have to really want to do it, you can't be tentative! It's easier when you're going faster.

The lower your gear , the more effectively you can "brake" by resisting with your legs.

Despite what some folks will tell you, you can not stop nearly as short this way as you can by using a good front brake.

See my article on Braking and Turning for a detailed explanation of this.


See the entry for skid patch in this glossary for how to choose sprockets to increase wear life of the rear tire if you use skip stops.

"Slick" or "bald" tires, those with no tread pattern, or perhaps just a bit of siping, provide the best performance for bicycles which are used on pavement.

Slick tires are smooth and silent-running, and have excellent traction. They have the lowest rolling resistance of all tire styles. Many people reject them because they look slippery, but in practice, they are not. Tread patterns on road tires are purely cosmetic, and have no practical value on hard, paved surfaces.

SLR Brakes
Shimano Linear Response, a series of friction-reducing modifications introduced in the late 1980's in the Shimano 105 group. The 105 SLR brakes (the best sidepull calipers ever made, in my opinion) incorporated: This system was replaced by "Super SLR" which is Shimano's name for double-pivot brakes.
Snake Bite
A colloquial term for a pinch flat, or rim cut, taken from the resemblance between the pair of holes in the tube and the puncture wound made by the fangs of a snake.
Snowflake Wheel
A novelty spoke pattern in which the spokes wrap around one another where they cross.
A rare type of bicycle for two riders sitting side-by-side. Not technically a "tandem" since that term implies one rider in front of the other.
Solid Axle
A plain hub axle, as opposed to a quick-release axle, which has a hole drilled through it for the quick-release skewer. A solid axle is secured to the frame by nuts.
A bicycle for one rider, as opposed to a tandem; a normal bicycle.

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