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Sheldon Brown's Bicycle Glossary Sa-So

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Spacing(Dropout/Axle)
Frame spacing is the inside distance between the two fork ends (drop outs), where the wheel fits in. This can easily be measured just by removing the wheel and holding a ruler up to the space where the wheel came out.

Hubs come with various length axles, but the axle length is not as critical as the overlocknut distance, since it is the locknuts that actually contact the frame ends. Overlocknut distance can't be measured directly without a caliper of some sort.

measure spacing

This frame has a spacing of 125 mm

The dropout spacing of a frame must match the overlocknut distance of the wheels that are to fit it.

Some standard spacings:

91 mm Low-end front hubs.
96 mm Older front hubs, especially French.
100 mm Modern front hubs.
110 mm Rear older track, coaster brake and other single-speed hubs. Also, front hubs for Downhill bikes with 20 mm axles.
114 mm Rear 3-4-speed .
120 mm Rear 5-speed, Ultra 6, newer track hubs.
126 mm Rear 6- and 7-speed (road).
130 mm Rear 7-speed (MTB) and 8- 9- and 10-speed (road).
135 mm Rear 7- 8- and 9-speed (MTB)
140 mm Rear tandem.
145 mm Rear tandem (newer models.)
150 mm Retro-Choppers, some Downhill and Freeride models.
160 mm Rear tandem (new Santana proposed standard.)
Overall axle length for quick release hubs is commonly 11 mm longer than the overlocknut distance listed, 5.5 mm on each side.

In practice, the axle can be quite a bit shorter than this...even 1-2 mm protrusion past the locknuts will suffice to locate the axle properly, so, when converting a hub to the next wider spacing, it is usually not necessary to replace the axle.

In the case of steel-based frames, it is a fairly minor matter to re-adjust the spacing of a frame to make it fit a different width hub. This process is commonly referred to as "cold setting."

Re-spacing is not generally feasible with aluminum, carbon fiber or titanium frames.

See also my Article on Frame Spacing

Spacing (Cassette/Freewheel Sprockets)
Center-to-center
Spacing
Sprocket Thickness Spacer Thickness Total Width
"Regular"
5-/6-speed
5.3 mm 1.85 mm 3.5 mm
Sun Tour "Ultra"
6-speed
5.0 mm 1.85 mm 3.15 mm
The above dimensions are approximate.
Before indexed shifting, spacing was not standardized.
Sun Tour
"Accushift" 6-speed
5.5 mm 2.0 mm 3.5 mm 30 mm
Shimano HG
7-speed
5.0 mm 1.85 mm 3.15 mm
Shimano IG
7-speed
5.0 mm 2.35 mm 2.65 mm
SRAM Freewheel
7-speed
5.0 mm 1.8 mm 3.2 mm
Sun Tour
7-speed
4.8/5.0 mm 2.0 mm 3 x 2.8 mm(L)
3 x 3.0 mm(H)
31.5 mm
Campagnolo
8-speed
5.0 mm 1.9 mm 3.1 mm
Sachs 7-speed &
1997 8-speed
5.0 mm 1.8 mm 3.2 mm
Sachs 1998+
8-speed
4.8 mm 1.8 mm 3.0 mm
Shimano
8-speed
4.8 mm 1.8 mm 3.0 mm
SRAM Cassette
8-speed
4.8 mm 1.8 mm 3.0 mm
SRAM Freewheel
8-speed
5.0 mm 1.8 mm 3.2 mm
Sun Tour
8-speed
4.8/5.0 mm 2.0 mm 3 x 2.8 mm(L)
4 x 3.0 mm(H)
36.5 mm
Campagnolo
9-speed
4.55 mm 1.75 mm 2.8 mm
Shimano
9-speed
4.34 mm 1.78 mm 2.56 mm
SRAM
9-speed
4.34 mm 1.8 mm 2.54 mm
Campagnolo
10-speed
4.12 mm 1.7 mm 2.42 mm
Shimano
10-speed
3.95 mm 1.6 mm 2.35 mm
Spanner
SPD pedals
"Shimano Pedaling Dynamics." See Shimano Models
SpearpointSpearpoint
A triangular extension of a lug, intended as an extra reinforcement. A spearpoint may be part of the lug, or may be welded on to the lug.
Speeds
Bikes with gear shifts commonly have anywhere from two to 30 different "speeds" altogether. The nomenclature for designating the number of speeds is confusing and somewhat inconsistent.

For bikes with only one gear shift, it's pretty simple. The number of gears is the number of positions.

When there are two separate gear shifters, it gets confusing. Most newer adult bikes have two derailers and shifters, one for selecting among the sprockets on the rear wheel, the other for selecting the chainwheel in front.

The traditional way for designating the number of speeds with such bikes is to multiply the number of rear positions (sprockets) by the number of front positions (chainwheels.)

  • Thus, a bike with 4 rear sprockets and 2 chainwheels was always called an "8 speed" (4 x 2)
  • In the late '50s, 5 speed rear clusters became the norm, and these bikes were typically called "10 speeds." For much of the '60s and '70s "10 speed" was practically a synonym for "bicycle."
  • In the early 1980s, a 6th rear sprocket became common, so those bikes would be "12 speed." If they had 3 chainrings instead of 2, they would be "18 speed."
Then it started to get confusing!
  • In the late 1980s, bikes started to come with 7 sprockets in back, so they would technically be either 14 speed or 21 speed, depending on whether they had 2 or 3 chainwheels. However, it was not unusual for cyclists to refer to these as "7 speed" systems, with the number of chainrings ignored.
  • In the early '90s, when the move to 8 sprockets in back occurred, "road" cyclists, who used two chainwheels, commonly referred to their bikes as "8-speed" (nobody remembered the 4 x 2 "8 speeds" from the early '50s.) These bikes could have been called "16 speed" but nobody did.

    However, touring and mountain cyclists, with 3 chainrings commonly referred to them as "24 speed."

  • This pattern seems to have largely continued: Bikes with two chainrings are commonly referred to by just the number in back, these days 9 or 10. Bikes with three chainwheels are more often referred to by the total multiplied number, i.e., 27 speed or 30 speed. Although a bike with 9 in back and two in front could technically be called an "18 speed", nobody does, so as not to cause confusion with 6 x 3 "18 speeds."
It is important to realize that the theoretical number of gears is not the same as the usable number of gears on a dual-derailer system, because there are some gear combinations where the chain angle is so extreme that those gears should not be used. In addition, there are often duplicated gear ratios, so a "27 speed" bike may actually only have 20 distinct, usable gears or so.

See also my article on Gear Shifting and my Gear Calculator Page. and my Speeds Page.

Speedway
Cycle Speedway is a type of dirt-track racing mainly popular in Britain and Australia. Riders race on a flat dirt track, usually two teams of two riders at a time. The bikes are generally fixed-gear machines with mountain-bike type wheels.

Here's a link to a Speedway Web site

Spider
A spider is multi-armed part of a crank to which one or more chainrings are attached.

Forged Crank

With most good quality cranks, the spider is an integral part of the right crank. Older, cheaper cranks commonly have a separate spider swaged to the right crank. Some newer cassettes also use a spider to connect the sprockets to the freehub body. This is done primarily to save weight.
Spline
A ridge on a surface of a part, usually used to prevent an otherwise circular part from turning. Commonly used on freewheels and cassettes where the sprockets attach.

Many newer bottom brackets use splines where the cranks attach to the bottom bracket spindle. Cartridge-type bottom brackets also use a splined wrench to install and remove the bottom bracket unit.

Square Taper, Octalink V1 and V2, ISIS Bottom Brackets

Some frame tubing has internal ribs to reinforce the tube; these are sometimes also referred to as splines.

Spin
  • Noun: a short bicycle ride for pleasure or exercise
  • Verb: to pedal at a rapid cadence
Spindle
See axle
Spinner
A cyclist who habitually pedals at a rapid cadence, as opposed to a "masher."
Spinning
  • Pedaling at a rapid cadence in a lowish gear.
  • A program of indoor exercising. "Spinning ®" uses stationary cycles, with a fixed gear and a heavy flywheel. A trainer guides a group of "cyclists" using loud music to regulate cadence.

    In this specific context, but only in this context, "Spinning ®" is a registered trademark.

Spoke
One of the wires connecting the rim to the hub of a bicycle wheel. See my article on wheelbuilding.

A conventional spoke has a swaged head, like the head of a nail, to keep it from pulling through the flange of the hub. Immediately after the head the spoke takes a right-angle bend, also known as the "elbow" of the spoke. (See also straight spokes) The outer end of the spoke is threaded, and a special nut called a nipple fits through the rim and screws onto the spoke threads.

Traditionally, most bicycles have had 36 spokes in each wheel. British bicycles, for years, used to use 40 spokes in the rear, and 32 in the front. This was a better system for the consumer, because the strength of the wheels was in better proportion to the stresses on them. It makes things easier for the manufacturers, however, to use the same number of spokes front and rear. This results in a front wheel that is needlessly heavy, and/or a rear wheel that is not as strong as it should be.

In the last decade of the 20th century, 32-spoke wheels became increasingly common. Manufacturers tout this as an advantage, because it saves a very small amount of weight (they don't mention that it is also cheaper!) For most cyclists, the reduced strength and reparability of 32 spoke rear wheels is a greater detriment than the very tiny improvement in performance they offer.

Formerly, spoke diameters were specified in terms of wire gauge, but the trend is toward specifying the diameter in millimeters.

Spoke length is measured from the inside of the elbow to the very end of the threads, most usually in millimeters.

Spoke weights

(courtesy of )
Brand Model Material Diameter Length
(MM)
Count Weight
(Grams)
Litespeed titanium 2.0 267 32 122
DT Revolution stainless 2.0/1.55 266 32 134
Wheelsmith 1.8DB stainless 1.8/1.55 266 32 135
FiberFlight Æro plastic   266 32 136
Wheelsmith 1.8DB stainless 1.8/1.55 267 32 146
DT 1.8DB stainless 1.8/1.6 266 32 156
DT 1.8 stainless 1.8 266 32 179
Wheelsmith 2.0DB stainless 2.0/1.7 273 28 159
Wheelsmith 2.0DB stainless 2.0/1.7 298 32 182
DT 2.0DB stainless 2.0/1.8 266 32 193
DT 1.8 stainless 1.8 291 16 97
Wheelsmith 2.0 stainless 2.0 264 16 107
Wheelsmith 2.0 stainless 2.0 266 16 109
Wheelsmith 2.0 stainless 2.0 267 32 218
DT 2.0 stainless 2.0 266 32 221
DT 2.0 stainless 2.0 289 16 120

Warning: Fiberflight spokes break and wheels fail catastrophically -- John Allen

Nipple weights

(courtesy of )
Brand Gauge/
Diameter
Material Weight Comments
Hi-E 15/1.8 aluminum 0.235 requires special socket wrench
Wheelsmith 14/2.0 aluminum 0.344
DT 15/1.8 brass 0.850 old-style disc-shaped
DT 14/2.0 brass 1.000 new-style trumpet-shape
Wheelsmith 14/2.0 brass 1.063
DT 15/1.8 brass 1.100 new-style trumpet-shape
DT 14/2.0 brass 1.140 old-style disc-shaped
Fiber Flight 14/2.0 plastic 7g/36 (claimed weight)

Warning: Fiberflight spokes break and wheels fail catastrophically -- John Allen

Spoke Numbers
See: 32-Spoke Wheels
Spoke Patterns
Spoked wheels may be laced in several different patterns. Most wheels use the semi-tangent pattern, less common is "direct" or "radial" spoking. Some rear wheels are laced "half radial".

There are also "novelty" or fad lacing patterns, including the "crow's foot" and "snowflake" designs. These patterns are eye-catching, but have no practical advantage.

Spoke patterns are discussed at some length in my wheelbuilding article.

Spoke Protector
A plastic or sheet-metal disc that fits between the cluster and the right-side spokes of a rear wheel. This is intended to prevent the derailer or chain from getting caught in the spokes, possibly causing very extensive/expensive damage/destruction to the wheel, the derailer, and the frame.

A spoke protector is not a necessity on a bike that is well treated, because the derailer can't go into the spokes if it's properly adjusted and if it is not bent. Bicycles which are subjected to rough handling, however, are prone to getting the rear derailer bashed in, and in such a case, the spoke protector can prevent very serious damage.

Spoon Brake
The earliest type of bicycle brake consisted of a lever which pushed a metal shoe against the tread of the tire. The part that pressed on the tire was shaped like a flat spoon, hence the name. Spoon brakes became obsolete with the invention of pneumatic tires, although spoon brakes on the front wheel, as an emergency back-up to a coaster brake, were still in production in less-developed countries as late as the 1980's.
Sport-touring Bicycle
Sport touring bicycles occupy a middle ground between touring and road racing bicycles. The meaning of this term has been changing:
  • Older "sport-touring" bikes, the typical 10 speeds of the 1970's bike boom,were solid, sturdy machines that differed from touring bicycles mainly in that they didn't have as wide a gear range. They could be used for moderately-loaded touring by riders strong enough to get along without serious low gears.
  • Current "sport-touring" bikes are more like road-racing bicycles which have had a triple crankset added. These bicycles have low enough gearing to let aging baby-boomers still get up the hills. Most bikes in this category are not well-suited for serious touring, because their wheels are too fragile, and they often are poorly designed so that there is not adequate frame clearance for fenders and touring-width tires.
Springer Fork
An early type of suspension front fork, usually using a linkage design with a simple steel coil spring, with no damping mechanism.
Sprint
  1. An all-out burst of speed, usually at the end of a race.
  2. A match sprint.
  3. British: a rim designed for tubular tires.
Sprocket
A toothed wheel or gear that is part of a chain drive.

The front sprockets are also commonly called chainwheels or chainrings. The term "sprocket" is perfectly correct to refer to either front or rear, but most adult cyclists use this term mainly to refer to the rear sprockets. The use of "sprocket" to refer specifically to a chainwheel is mainly confined to BMX usage.

The rear sprockets individually are also commonly called cogs or gears; as a group they are referred to as a block, cassette, cluster or freewheel.

Sprung/Unsprung Weight
The sprung/unsprung weight ratio is a critical factor in determining how well any vehicle will hold the road on rough surfaces.

The "sprung" weight is the weight of the part of the vehicle and its payload which is held up by the springs. In the case of a suspension-equipped bicycle, the sprung weight includes most of the frame, and the rider. In the case of a rigid-frame bicycle, the "sprung" weight consists of the rider's trunk and head while the rider is off the saddle, carrying his or her weight on bent knees/elbows.

The "unsprung" weight is the weight of the wheels and the parts of the suspension that move up and down with the wheels as they track over bumps.

When a bump lifts a wheel up, the spring compresses. After the wheel passes over the bump, the spring pushes the wheel back down into contact with the ground. In the case of a vehicle with a low sprung/unsprung weight ratio, such as one with heavy wheels and a light rider, the spring will not be able to push it back into contact with the ground as fast as the same spring could push a lighter wheel.

If the rider is light, the spring force will also be light, so it will not be able to push the wheel back down as fast as the stronger spring that would be used with a heavier rider could push the same wheel.

If the rider is light, but the spring is strong, the rider will not get enough benefit from the suspension, and the strong spring will lift the rider as well as the wheel.

Squirm
When a knobby tire is used on a hard surface, the knobs can bend sideways under load. This effect can cause poor cornering traction, especially on tires with tall knobs at the sides of the tread. Squirm can cause a sudden and abrupt loss of cornering traction, with little warning.
S.R. ®
A slippery abbreviation, with two different meanings:
  • As a trade name, it is an alternate form of Sakae Ringyo, a major Japanese maker of aluminum parts, particularly cranks and seat posts. In the 1990's, S. R. bought what was left of the bankrupt Sun Tour, and the combined companies are now known as SR-Sun Tour.
  • The abbreviation "S.R." is also commonly used in want ads for older racing bicycles, where it refers to the old top-of-the-line Campagnolo Super Record gruppo.
SRAM ®
Based in Chicago Illinois, the SRAM Corporation is best known as the manufacturer of GripShift twist-grip shifters. SRAM also manufactures derailers, and purchased the bicycle division of Sachs, manufacturer of internal-gear hubs and bicycle chains.

The name "SRAM" is an acronym from the initials of the founding partners.

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