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Sheldon Brown's Bicycle Glossary Sa-So

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Stack bolt
The stack bolts are the small bolts that hold the chainwheels to the spider of a crank.
Stack Height
The stack height is the vertical space taken up by the headset. With a conventional threaded fork, the steerer tube is longer than the head tube by some amount. If a headset is chosen with a stack height greater than this difference, there may not be enough of the steerer free above the upper bearing race for the keyed washer and lock nut to be installed. In the case of thread less headsets, the stack height also includes the height of the part of the handlebar stem that clamps to the steerer.
Stainless Steel
A family of steel alloys, usually containing 10-20% chromium, among other alloying elements. Stainless steel is rust-resistant, and very tough, but is generally not the best choice in applications where surface hardness is of primary importance, such as bearings. Stainless steel also has somewhat lower yield strength than steel alloys optimized for that characteristic, and is somewhat more difficult to weld, so it has only rarely been used for frame tubes. [Last sentence added by John Allen]

The primary bicycle application for stainless steel is for spokes. Virtually all modern high-quality spoked wheels have stainless-steel spokes.

Stainless steel is also used for high quality control cables.

Standover Height
One of the prime dimensions of a bicycle, this refers to the height of the top tube above the ground. If the standover height is too tall for a given rider, mounting and dismounting are awkward and dangerous.

Conventional wisdom is that the standover height should permit 1-3 inches (2-8 cm) of clearance between the top tube and the crotch of a rider straddling the frame, for road use. For off-road riding, considerably more clearance is required. See my article on Frame Sizing.

Two members of the Starley family in England were great pioneers in the early days of cycling. James Starley was instrumental in the development of the high-wheeler bicycle. He produced the first all-metal bicycle, and invented the tangent-spoked wheel, which is used to this day. His nephew J. K. Starley designed and built the "Rover," the first commercially successful rear-drive "safety" bicycle, which is the ancestor of all modern diamond-frame bicycles.
Star Nut
Star Fangled ® Nut
A special nut that is designed to be hammered into the steerer of a bicycle with a thread less headset, such as a Dia Compe "Aheadset" ®. The adjusting bolt screws into the "Star Fangled Nut."

The star-fangled nut has two barbed steel flanges that allow it to be forced downward into the steerer, but which prevent it from moving upward.

If you ever need to remove a star nut, the easiest way is by driving it down and out the bottom of the steerer with a hammer and punch.

Star nuts are only for use on metal steerers and should never be used on carbon steerers. Forks with carbon steerers generally come with special expansion plugs that serve the function of a star nut, without the sharp edges that might damage the fragile carbon steerer.

Star nuts are available in several diameters to fit different types of forks.

A thin, usually straight, structural member: Seatstay, chainstay, fender stay, mixte stay.
A bicycle used for motor-paced racing, usually behind a motorcycle.
An alloy of iron and carbon, usually containing between 0.2 and 1.5 percent carbon, often with other constituents such as manganese, chromium, nickel, molybdenum, copper, tungsten, vanadium or other metals, depending on the characteristics desired. Steels used in bicycle construction are commonly alloyed with chromium or manganese and molybdenum. Chromium-molybdenum or "cromoly" (CrMo) steel, also known by the numerical designation 4130, is particularly popular for high-quality bicycles.

Although steel is used for most high-quality bicycle frames, the use of steel instead of aluminum for many parts is often the result of penny pinching. Nobody should have to ride a modern bicycle with steel rims, brakes or handlebars. The only reason steel is now used for these parts is to scrimp on costs.

This was not always the case. As recently as the 1960's, steel was favored for many of these parts, particularly by the British. Indeed, for many years, Raleigh's slogan was "The All-Steel Bicycle". Steel parts of this era were often high in quality.

British term for the Captain of a tandem.
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, headset and a thread less or pinch-bolt type stem if one is used.
Steering Axis
The centerline of the head tube/headset, the axis about which the handlebars and fork turn for steering and balancing.
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.

  • "Thread less"-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 "thread less" 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 or quick release. These are most often seen on folding bicycles, because this design permits the use of a quick release.

  • "Adjustable" stems, (also known as "Major Taylor outriggers", after the cyclist who popularized them and possibly invented them), have the handlebar clamp unit mounted on a moveable part, permitting setting different amounts of forward extension.
Stem->Steerer fitting dimensions
Nominal size Stem diameter
Outside diameter
(Thread less stem size)
Inside diameter
(Wedge-bolt stem size)
1" Standard (25.4 mm) 7/8"(22.2 mm)
1 1/8" (28.6 mm) 1" (25.4 mm)
1 1/4" (31.8 mm) 1 1/8" (28.6 mm)
BMX/ O.P.C. bikes .833"(21.15 mm)
French 25 mm (obsolete) 22mm
Stem->Handlebar fitting dimensions
Size Application
22.2 mm 7/8" Steel bars. Mainly BMX, older Mountain bike bars.
23.8 mm 15/16" Obsolete British size for steel handlebars, common on older 3-speeds. This size was also used for steel drop bars.
25 mm Obsolete French size.
25.4 mm 1" Standard I.S.O. size, used on the vast majority of newer bicycles.
This is sometimes incorrectly called "mountain bike" size.
25.8 mm Unofficial in-between size used by some Italian handlebar makers for handlebars designed to be usable in either ISO (25.4) or Italian (26.0) size stems.
26.0 mm Italian standard for drop bars, other bars made to fit Italian stems and some high-end aftermarket drop bars.
This is sometimes incorrectly called "road" size.
26.4 mm Older Cinelli and Cinelli copies. Cinelli changed over to 26.0 in 1998.
27 mm Titan (obsolete).
31.8 mm 1 1/4" Road oversized.
"Road" vs "MTB." A common, misunderstanding makes a false distinction between "road" and "mountain" size stem/handlebar fitting. The vast majority of bicycles use the standard ISO 25.4 mm/1" size, whatever style of handlebar is used. High-end road bikes assembled with custom parts groups often use expensive aftermarket bars and stems, which do predominantly come in the Italian size, since the major makers of expensive bars/stems for road bikes are Italian. Non-Italian parts makers attempting to compete for the high end market often offer both sizes.

Height / Angle / Reach

The range of handlebar positions available from a given stem depends on its height, angle and reach (extension.) Unfortunately, measurement procedures for determining these dimensions are not well-standardized in the industry, making it difficult to compare one stem with another based on the dimensions.

  • The height dimension is normally the overall height, measured along the line of the column.

  • Angle / rise may be measured either from the steering axis or perpendicular to it. Thus, a stem with the extension at a right angle to the column may be described either as a 90° or 0° stem.

  • Reach / extension is normally measured center-to-center along the direction of the extension.

The custom of measuring reach along the line of the extension means that two stems of the same nominal reach will provide a different distance between the steering axis and the handlebar center, if they have different angles.

"Pop Top " Stems

Many newer stems use the "pop-top" attachment system for the handlebars, permitting the stem to be swapped without disturbing the handlebar grips/tape or brake/shift controls.


See also Hands Up! Adjusting Handlebar Height

Note: Steerers are butted at the bottom, so the hole in the steerer is constant-diameter until near the bottom, then the walls taper inward in the butted section.

It is vitally important that the stem extender (or stem) not be inserted so far that the wedge is installed where the steerer is narrowing, or it could come loose unpredictably.

When this happens, only the edge/corner of the quill or wedge contacts the steerer, and it is trying to "grab" a slanted surface.

This is sometimes a problem on smaller frames if you try to insert the stem or a stem riser too far down into the steerer.

Stem Inserted Too Far

Illustration by Nicholas Flower

The term "stem" is sometimes also used to refer to a valve.

Stem Shifter
A type of shift lever which mounts on the shaft of the handlebar stem. These were popular in the late '70's and early '80's because they permitted shifting without having to lean down to reach down-tube mounted shift levers. Stem shifters, along with brake extension levers, encouraged riding using only the top of drop handlebars. This riding style was popular at the time, because many casual cyclists bought bicycles with drop bars for reasons of fashion and style, even though drop bars were not suited to their low-intensity riding style.

Unfortunately, this riding position gives rather poor control of the bicycle, mainly because the hands are too close together for good steering control. Also, stem shifters are difficult to shift precisely, because with the shifters behind the stem, there is nothing against which to rest the hand. Most stem shifters are friction shifters, worsening the problem.

Stem shifters also present a danger in a collision. Depending on what gear you have selected, stem shifters can be like having a dull knife aimed at your groin!

If your bike has stem shifters, consider upgrading to something safer and more convenient.


A Shimano buzzword standing for "System Total Integration". This normally is used to refer to Shimano's combined brake lever/shift lever systems, particularly those designed for drop handlebars. S.T.I. is similar to Campagnolo's Ergo system. S.T.I. uses the main brake lever, pushed inward, to select larger sprockets, and a smaller, auxiliary lever inside the brake lever to select smaller sprockets. [S.T.I has the advantage that it is not necessary to remove a hand from a brake lever to shift, but the disadvantage that the lever returns to the same position after every shift, so you can't tell by feel which sprockets you have selected until you get to the last one. And then you may have shifted to a crossover gear with a bad chain angle. An alternative for drop bars is bar-end shifters, which keep the hands on the handlebars, though not on the brake levers, and change position with each shift. Bar-end shifters are much less expensive, and less complicated, too. -- This comment added by John Allen]

See also the article on this site about repair of STI levers.

Sting-Ray ®
Schwinn trademark for a family of wheelie bikes. These have become quite valuable to collectors.
A tandem rider who is not responsible for steering, usually the rear rider(s), as opposed to the captain. The term comes from the workers who shoveled coal to power steam trains and steamships.
Stoker Lever
A dummy brake lever hood assembly. These are designed to act as a hand rest for a tandem stoker as the brake lever hoods do on a solo with drop handlebars.

On fixed-gear bicycles that only have a single brake, some riders install a stoker lever on the other side of the handlebar for symmetry.

A child stoker, particularly one using a kidback tandem. I coined this term in November, 1995.
Italian for "road."
Straight gauge
Not butted, i.e., a tube which has the same wall thickness from end to end, or a spoke which has the same thickness from end to end.
Straight Spokes
Originally, spokes didn't have the elbow, and they were straight from one end to the other. They required a special type of hub, which was harder to manufacture than conventional hubs. Straight spokes are also harder to lace up, and tend to revolve when the nipple is turned.

The modern bent design supplanted"straight pull" spokes in the 1890's. Since no bicycle technology ever disappears entirely, straight spokes get re-invented from time to time, but have not met with much commercial success in the last hundred years. They are seen on some "boutique" wheels.

Stress Relieving
New spokes have residual stresses manufactured into them when they are bent at the elbow. It is impossible to build a reliable wheel without neutralizing these stresses. This is accomplished by bending or otherwise applying extra tension to the spokes. For more detail on this see the stress-relieving section of my Wheelbuilding article.
Stress Riser
A stress riser is a notch, crack or other irregularity in the surface of a part which creates a starting part for a crack or tear. A familiar household example of stress risers is cellophane: It is fairly difficult to start a tear in a straight edge of a piece of cellophane, but once a tear has started it is almost impossible to stop.

A similar effect occurs with other materials, including those used to build bicycle frames. Good design avoids placing stress risers in heavily loaded areas of the frame.

Sturmey-Archer ®
The best-known manufacturer of internal-gear hubs. See my article on English 3-Speeds.

This site also features a commemorative brochure celebrating the first fifty years of Sturmey-Archer 1902-1952, and a page on the ASC three-speed fixed gear hub.

Jane Thomas originated and I have re-posted excerpts from the 1956 Sturmey-Archer service manual.

  • A steel post sticking out from the tread of a tire to provide traction on ice.
  • Alternate term for cantilever boss.
See Shimano Models
Originally a Japanese company, the first manufacturer of inexpensive cotterless cranks , and for many years Japan's leading manufacturer of cranks. Sugino cranks are generally of very good quality, like most Japanese products.
Suicide Hub
A rather alarmist and silly name for a freewheel hub used as a fixed-gear hub.

Any standard-thread freewheel type hub will also accept a fixed-gear ("track ") sprocket . This is a common technique for converting an older bike to fixed gear on the cheap.

Despite the silly name, this is no more dangerous than using a freewheel, as long as you keep front and rear hand brakes installed.

Suicide Levers
Extension levers.
Sun Pinion
The middle gear wheel in a planetary gear system.
Sun Tour ®
From the early '70s to the mid '80s, Sun Tour (Maeda) was the most important Japanese maker of bicycle parts. Sun Tour invented the slant-parallelogram design for rear derailers, and made the best-shifting derailers in the world for many years, until the patent ran out.

Other major Sun Tour innovations included:

  • "Power Ratchet" shift levers, which used a ratchet mechanism to disengage the friction mechanism from the lever when it was being pulled against the tension of the derailer's return spring. This created a lighter lever action than other friction-type shift levers.
  • The first widely distributed freewheels using splined sprockets.
  • Asymmetrical sprocket teeth to improve shifting.
  • Thumb shifters.
Sun Tour also marketed several technologies licensed from other companies: Unfortunately, Sun Tour failed to maintain the inventive spirit that put it in the lead in bicycle components, and Shimano's success with indexed shifting left Sun Tour playing catch-up. Sun tour never caught up, and it became almost impossible to sell a bicycle that didn't feature Shimano shifting systems. As a result of this, along with poor customer service, Sun Tour went bankrupt in the early 1990s. For details of this story, you may read Frank Berto's article "Sunset for Sun Tour"

The Sun Tour name has been purchased and revived by Sakae Ringyo, though the new SR/Suntour parts are not compatible with the original Japanese SunTour parts.

For more, see the page about SunTour history.

S.U.P. ®
Soudé Usine Procès, (Welded Machined Process) Mavic's name for rims which have a welded seam, with the braking surfaces turned on a lathe after welding.

See also Machined Rim Sidewalls

See: BSX/Supercross
Superglide ®
Shimano's system for improving front shifting. It consists of specially-shaped teeth and ramps on the sides of some chainwheels. Superglide chainwheels, like Hyperglide sprockets, come in sets designed to work together, so you won't get the full benefit of the system if you substitute individual chainwheels.
Superman Position
A novel riding position, invented by Grahme Obree, using special handlebars which stretch the hands straight out in front of the rider.
Super Record
The Top-of-the-line Campagnolo parts group of the mid '80s. It shared many parts with the Nuovo Record group, but was lightened by the use of titanium fasteners and cut-away chainrings, etc. Super Record is the most sought-after group by collectors and restorers of classic racing bicycles.
A Bianchi trademark. In the 1980s, Bianchi used a "Superset" design, where the down tube and chainstays were supposed to be a bit heavier-gauge than normal, and the upper parts of the frame a bit lighter. The idea was to stiffen up the drivetrain. This was based on standard diameter round tubing, to fit standard lugs.

The later (1990s) "Superset II" design required special lugs, because it used an oversized down tube, ovalized at the bottom, also oversized oval chainstays. Bianchi was unique in using oversized and ovalized tubing with lugged construction, because the tooling for the special lugs was quite expensive.

"Suspension" refers to devices using some kind of spring to protect the rider and/or the bicycle from the effects of riding on rough surfaces. Modern suspensions usually include some sort of damping mechanism.

In addition to adding to the comfort of the rider, suspension systems improve traction on bumpy surfaces, by keeping the tires in more nearly constant contact with the surface. (See sprung/unsprung weight) They also help protect the wheels from damage, by allowing them to spring out of the way when they hit something forcefully.

Suspension-Corrected (Fork)
Suspension forks have more room above the top of the tire, to allow the suspension to move. Frames built for suspension forks are designed so that the bottom end of the head tube will normally be higher up to make room for the suspension fork's travel.

Suspension-corrected rigid forks mimic this geometry: they have longer blades to hold the head tube up to the same height a suspension fork would. If you desire to replace a suspension fork with a rigid fork, you should opt for a "suspension-corrected' rigid fork to preserve the frame's normal geometry.

Sutherland's Handbook for Bicycle Mechanics
Sutherland's Handbook for Bicycle Mechanics by by Howard Sutherland, is the technical reference par excellence for bicycle mechanics. It is the source of much of the information included in this glossary, and much more. Every bicycle shop should have at least one copy of this indispensable reference work. It is available through bicycle distributors.

It is published by Sutherland Publications, Box 9061, Berkeley, California 94709.

Swaging is the process of shaping metal by impact, particularly as making a thin part thicker. For instance, the heads on bicycle spokes are produced by "swaging" the end of the spoke wire. Swaging, unlike forging, does not usually involve heating the metal to a high temperature.

Swaged Cranks

Cheaper cranks use swaging as a means of attaching the spider or chainwheel to the right crank.

Better-quality cranks are made with the right crank and spider a single forging or casting, with no joint to fail. Forged cranks are not only more durable, but the chainrings tend to run straighter, providing better shifting performance.

Swaged Crank Forged Crank

Swaged cranks were formerly common, but are now seen mainly on low-end bicycles. A swaged crank is an iffy proposition on a tandem, a fixed-gear bicycle, or a bicycle with a coaster brake, because applying force in both directions runs a substantial risk of loosening the chainwheel so it freewheels in both directions.

Short Wheel Base (recumbent)
Linear recumbent
A Linear SWB recumbent
Swiss bottom bracket threading is the same diameter and pitch as French, but differs in that Swiss fixed cups are left (reverse) threaded, while French fixed cups, like the adjustable cups, are right threaded.

See my Bottom Bracket "Crib Sheet."

Symmetric ® (SunTour) Shift Levers
These shifters are mainly seen on Japanese "road " bikes from the 1982 model year. They use an "aero" mount where the shifters attach just above the top tube, instead of on the sides of it. Most of them used a special proprietary braze-on mount that isn't interchangeable with anything else.

These shifters are a bit problematical. Like other "friction " shifters, the lever friction is regulated by the bolt the lever pivots around. If you tighten that bolt a bit, the derailer will more or less stay in position. If you tighten it too much, it will be hard to move the lever. .

Unfortunately, these levers are a fundamentally flawed design. SunTour built in a special cam mechanism to make the front derailer move slightly to "trim " its position as you shifted the rear. This was a good idea -- it is a wonder that nobody else has taken it up -- but poorly executed.

The automatic "trimming" mechanism generally only works in one direction. Which direction that will be depends on the relative friction settings of the front and rear levers. Theoretically there's a particular balance point where it works right, but in practice this never works.

Sync chain
The sync, or "timing" chain on a tandem connects one bottom bracket to another. There is a synch chain for each stoker, so, for instance, a triplet has two synch chains.

Sync chains generally connect equal-sized chainwheels, so the mechanical advantage is 1:1. This is true for all sizes of sync chainwheels, as long as they are both the same size. Smaller sync chainwheels, however, put a greater stress on the sync chain, the frame, and the bottom bracket bearings, so it is a mistake to make them too small in an attempt to save weight. Typical sizes are in the range of 38 teeth and up.

See also my article on Tandem Sync Chains.

Synchro ®
In the late 1980's, Campagnolo needed to respond to Shimano's S.I.S. indexed shifting system. Campagnolo's first attempt was called "Synchro ®."

It was Campagnolo's wish to make a system that would be compatible with its older derailers and other products, to provide an easy upgrade path for existing customers. This was a laudable goal, but turned out to be impractical.

The Synchro (and Synchro 2) down tube shift levers had replaceable, color-coded "indexing discs" with detent notches at different spacings. There were quite a few different indexing discs available for different freewheel models and spacings.

The problem that sank Synchro was cable travel. Campagnolo derailers had always used a very short cable travel from gear to gear. The shorter travel came with higher tension, and these two factors exacerbated issues of cable friction and stretch. As Shimano also discovered, a key to good indexing is long-travel, low-tension cable setups. Shimano also made a misstep with this: its original 1984 Dura-Ace S.I.S. system used a fairly short cable travel, requiring unusually-high precision in associated parts. When Shimano "trickled down" S.I.S. to the 600EX group in 1986, it went with a longer cable travel, which became the standard for the rest of the Shimano line. This led to a decade of incompatibility between Dura-Ace and the rest of the Shimano line, only resolved in 1997 when Dura-Ace went to 9-speed and lengthened the cable travel to match the rest of the line.

Currently, Campagnolo's shifters and derailers use an even longer cable travel than Shimano does.

Synchro derailers and shift levers are incompatible with anything else, and the Synchro system worked so poorly that it is not a good idea to try to set the system up on a bike you intend to actually ride.

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