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Sheldon Brown's Bicycle Glossary/D
- Dampening
- Damping
- Death Cleats
- Death Fork
- Death Grips
- Demultiplier (Démultiplicateur in French)
- Delta Brakes (Campagnolo)
- Deore → Group
- Department Store Bicycles
- Derailer, Dérailleur
- Derny
- Detent
- Development
- Devil Take the Hindmost
- D.H.
- Dia Compe ®
- Diamond Frame
- Die
- Direct-Pull cantilever
- Dish
- Dish Stick
- Disc Brake
- Disc wheel
- Domed and Slotted
- Domestique
- Donkey-Back
- Double
- Double-Butted
- Double-groove Handlebars
- Double-Pivot → Dual-Pivot
- Double Shifting
- Double-sided Hub
- Down Tube
- Downhill Racing
- Downshift
- Drag Brake
- Draft
- Drainpipe
- Draisine
- Driver
- Drivetrain
- Drop
- Drops
- Drop Bolt
- Drop Handlebar
- Dropout
- Drum Brake
- Dry Rot
- D.S., N.D.S.
- Dual-Pivot
- DT ®
- Dual Suspension
- Dunlop
- Dura Ace
- Duralumin, Dural
- Dustcap
- Dyna Drive ®
- Dynamo
Dampening
The act of making something damp. A common malapropism for "damping"
Damping
Causing vibrations to stop, usually by the use of friction. In suspension systems, this is commonly done either by direct rubbing friction, or by pistons forcing fluids through small openings.
Death Cleats
Clipless pedals that require a manual release before the rider can disengage the shoes from the pedals. This term refers mainly to the Cinelli M71 pedal system, the first clipless binding system.
Death Fork
The aluminum fork used on Lambert and Viscount bicycles in the 1970's. Don't ride on one of these!
Death Grips
Slang term for Extension levers.
Demultiplier (Démultiplicateur in French)
A bell-crank-like device formerly marketed by Simplex as an accessory to bar-end shifters. It attached to the seat tube just above the bottom bracket. It served the function of a cable guide, but had two separate cables attached to it. The cables attached to a pivoting part at different radii, so the mechanical advantage was altered by this unit. This made it possible to shift reasonably well with the bar-end shifters, even though there was a stone-age Simplex derailer at the other end.
The cable from the shifter connects to point "1", acting on radius "A".
The cable to the derailer connects to point "2" acting on radius "B".
The cable travel at the upper section is increased by the ratio A/B.
Cable tension on the segment between the shifter and the demultiplier is reduced by the ratio B/A.
The Jtek ShiftMate is a similar device, used to match indexing when shift controls are mismatched with a different derailer.
Since the popularization of direct-pull cantilevers, such as Shimano's V-Brake, several companies have introduced new versions of the demultiplier, for example the Quality Bicycle Products Travel Agent ®, to permit conventional levers to work with these brakes.
Mark Bulgier Photo https://www.flickr.com/photos/61312162@N02/
Delta Brakes (Campagnolo)
Early '80s "ærodynamic brake calipers from Campagnolo. These used a four-bar linkage which resulted in a change in mechanical advantage as the brake shoes wore.
See Jobst Brandt's analysis of this design.
Department Store Bicycles
There are two entirely separate bicycle industries. Bicycles intended for real use are sold primarily in bicycle shops, and also, to some extent, in sporting-goods stores. Bicycles sold through this side of the industry are well made and sturdy, and are sold fully assembled, tested and guaranteed.
A parallel business uses department stores and discount stores for distribution. They concentrate on a much lower price segment, and sell a drastically inferior product. The bicycles sold in department stores are made as cheaply as possible, from the poorest materials available. The average department-store bicycle is ridden about 75 miles in its lifespan from showroom floor to landfill. The manufacturers know this, and build them accordingly. Department-store bicycles are most commonly sold in a partially disassembled and un-adjusted condition. ******
Derailer, Dérailleur
A mechanism for moving the chain from one sprocket to another to change gears on a multi-speed bicycle.
A typical derailer consists of a parallelogram which moves a cage. In the case of a rear derailer, the cage has two chain pulleys, a jockey pulley and a tension pulley. Different derailers have different capacities to handle different gear ranges. Also commonly spelled in the French style "Derailleur."
An extensive article on Derailer Adjustment is available on this site.
Britain's Cyclists' Touring Club Website has a good article on derailer gearing.
Derny
A special motorcycle designed for use in motor-paced track racing events, as well as some road events and for training. (Named after Roger Derny, founder of a French company that made small motorcycles, but also in this special case a pun on "dernière", which means "last". Also see motorpace and Wikipedia article)
Detent
A click stop, a place where a mechanism is designed to fall into one or another specific settings. This usually consists of one of several valleys in a track, along which a spring-loaded part slides. When the spring-loaded part is released, it tends to fall into one of the valleys. This is commonly used in bicycles in indexed shifting systems.
Development
Development (also known as rollout), is one of the three comprehensive systems for numbering the gear values for bicycle gears. Development is the distance the bicycle travels for one crank revolution, and is usually measured in meters. Development can be calculated by dividing the chainwheel size by the rear sprocket size, multiplying the result by the wheel diameter and by pi (3.1416). See also gear inches and gain ratios.
You can calculate gain ratios., gear inches or meters development with my Online Gear Calculator or with your slide rule
Devil Take the Hindmost
D.H.
Down Hill, specifically, down hill racing. This activity goes against the spirit of cycling more than any other branch of the sport, since it is the only branch of cycling which is not powered by the riders' muscles. This sport should, perhaps, be considered a branch of motorcycling, not cycling.
Dia Compe ®
The leading Japanese brake supplier before Shimano acquired a near monopoly on the Japanese parts business. Dia Compe used to have a working relationship with Sun Tour, and made the brakes labeled "Sun Tour." Dia Compe components have a well-deserved reputation for quality.
Dia Compe first made a major impression on the bicycle industry in the late '60's, by inventing extension levers for drop-bar brakes. At that time, Weinmann was the leading brake manufacturer. Dia Compe's extension levers were so popular that Weinmann entered into a licensing agreement with Dia Compe, allowing Dia Compe to copy Weinmann's brakes in return for letting Weinmann copy Dia Compe's extensions.
More recently, Dia Compe has revolutionized the design of headsets, with its "AheadSet" threadless headsets.
Diamond Frame
This is the standard design for a bicycle frame, and has been for over a hundred years, since it supplanted the cross frame. It is one of the most nearly perfect pieces of design known, due to the extreme amount of refinement it has undergone over the last century, and its purity of form. It is unlikely that the diamond frame will ever be surpassed as a way to build a rigid-frame bicycle using joined tubes as a construction medium.
This is not to say that the diamond frame is the end-all and be-all of bicycle design. Monocoque construction with suitable materials has real merit, and the design of bicycles with rear suspension is at a stage where many different designs appear viable.
Die
- A tool for cutting external threads. It takes the form of a nut with flutes cut in the threads and usually has a taper at the end that is intended to start the thread. There are only a few standard sizes used on bicycles:
The corresponding bolt-like tool for cutting internal threads is called a tap.Size Application System 6 mm Brake center bolts 25.0 x 1.0 mm Steering columns French 1" x 24 tpi Steering columns British, Italian, I.S.O. 1 1/8" (28.6 mm) x 26 tpi Steering columns oversized 1 1/4"(31.8 mm) x 26 tpi Steering columns oversized - The mould-like forms used for forging are called tools and dies. (The bottom, stationary half is the die, the upper, moveable part is the tool.)
Direct-Pull cantilever
A cantilever brake in which the housing stop is on one arm, and the inner cable crosses straight across to an anchor bolt on the other arm. The best-known direct-pull brakes are made by Shimano, using their trademark "V-brake."
This type of cantilever does not use a separate transverse cable. It has two tall arms, one of which has a housing stop and the other the anchor bolt. The exposed part of the cable runs horizontally from one arm to the other.
Direct-pull cantilevers have more mechanical advantage than other brakes, so they require special hand levers with less-than-average mechanical advantage to keep the overall mechanical advantage in a useful range.
See my article on Direct-Pull Cantilevers.
Dish
A bicycle wheel should have the rim centered directly in line with the frame. The forkends are symmetrical with respect to the frame, and the hub axle locknuts (or equivalent surfaces) press against the insides of the dropouts.
Wheels should be built so that the rim is centered exactly between the axle ends on the hub. In rear wheels, the spokes attach to flanges which are not symmetrical about the centerline...the right flange is usually closer to the centerline than the left flange, to make room for the sprocket(s).
When rear wheels are built properly, the spokes on the right side are made tighter than those on the left side, pulling the rim to the right, so that it is centered with respect to the axle (and to the frame.) Viewed edgewise, a rear wheel built this way resembles a dish, or bowl, since the left spokes form a broad cone, while the right spokes are more nearly flat.
By extension, the term "dish" is used as a general synonym for accurate centering, even in the case of symmetrical wheels.
See also my Wheelbuilding article.
Dish Stick
A tool for checking the dish of a wheel. It has the form of a curved stick with an adjustable feeler near the middle. The two ends of the stick rest on the side of the rim, 180 degrees apart, and the feeler is adjusted to just touch the locknut or other locating surface at the axle end. The wheel is then inverted, and, if it is correctly "dished" the three points will all contact the corresponding points on the second side of the wheel.
Disc Brake
A hub brake, similar to an automotive disc brake, consisting of a disc which bolts or threads onto the hub and a caliper attached to the frame or fork which squeezes on the disc. Disc brakes are better able to dissipate heat than rim brakes, making them popular for downhill events and for tandems.
Some early disc brakes had a reliability problem, in that outer part of the disc could break away from the part that attached to the hub, causing complete failure with no warning whatever. When the rider would squeeze the brake lever, it would feel solid, as the caliper was gripping the disc securely...unfortunately, it would do nothing to stop the bicycle!
Disc brakes are becoming increasingly common, partly because they work in wet conditions when rim brakes don't, partly because they don't cause wear to rims, and partly because of fashion.
See our article about disc brakes.
There have been concerns about the safety of front disc brakes in conjunction with quick-release skewers. See James Annan's article on this topic.
Disc wheel
A disc wheel is a wheel with solid sides, instead of spokes. Although disc wheels are heavier than spoked wheels, they have less air resistance, and permit a cyclist to go noticeably faster. They are not usually used at the front, because they can cause severe handling problems in crosswinds. They are not usually used for hilly conditions, because the added weight is too much of a disadvantage on the climbs.
The illustration is from Archibald Sharp's Bicycles and Tricycles, originally published in 1896, republished by the M.I.T. Press in 1977.
The front wheel has cutouts to reduce steering problems that result from crosswinds when disc wheels are used on the front.
Domed and Slotted
Refers to fork blades, chainstays and seatstays which are tapered in a rounded (domed) shape at the end which receives the dropout, and slotted for insertion of the dropout's tang. The dropout is then brazed into place. ****
Domestique
In a racing team, a "domestique" (French for domestic servant) would be a "foot soldier" of the team. Domestiques are in the race only to assist the team leaders. This assistance can take many forms:
- Providing a draft when a leader needs help keeping/catching up.
- Carrying extra water bottles and food for the leaders.
- Blocking opposing riders from passing.
- Giving up a bike to a leader who has had a crash or other mechanical difficulty.
Donkey-Back
A "donkey-back" is a setup for a multi-rider tandem, where the rearmost stoker's crankset is concentric with the rear hub. This stoker's saddle is mounted on an extension that resembles a pannier rack.
It requires a very special rear hub with an axle within an axle. There is a sync chain running from the donkey back's cranks forward to the penultimate stoker's crankset.
Donkey backs were used primarily around the turn of the century as pacing vehicles (usually quads) for track races (a task later taken over by special motorcycles, such as the Derny). The donkey-back design placed the rear stoker back over the wheel, to give the racer on the solo the best possible draft. Some donkey-backs have been sold as utility tandems.
Double
- A crankset having two chainwheels.
- A double century; 200 miles.
Double-Butted
Butted at both ends. This term is commonly used to refer to frame tubes and spokes, although some prefer the term "swaged" when discussing spokes.
Double-groove Handlebars
Many newer drop handlebars have an indented groove or grooves in the curved section above the brake levers.
- Single-groove handlebars have such a groove along the front edge only, to accommodate the brake cable running from a modern "æro" brake lever.
- Double-groove handlebars have, in addition, a groove on the rear edge of the bar, to accommodate the shift cables from Campagnolo (or Sachs) Ergo shifters. If a double-groove handlebar is used without Ergo shifters, it is a good idea to tape a short length of housing into the groove, or to use a special rubber filler piece made for the purpose.
Double Shifting
The act of shifting both the front and rear derailer at the same time. This is fundamental to the use of half-step or alpine gearing, unnecessary with crossover gearing.
Double-sided Hub
A hub which can be fitted with a sprocket on each side, so that a one-speed bicycle can have two different gears, which are selected by removing the wheel and turning it around so that the other sprocket may be used. Also known as a "flip-flop" hub.
The most common application for double-sided hubs is for fixed-gear bicycles. Many fixed-gear fans have a fixed sprocket on one side, and a freewheel on the other, using one or the other as conditions change. This is discussed at more length in my article on Fixed Gear Road Bicycles.
Down Tube
The frame tube that runs diagonally up from the front of the bottom bracket up to the lower end of the head tube.
Downhill Racing
I consider this fad to be bad for cycling, and contrary to the spirit of cycling. It is effectively just a variant form of motorcycle racing, since most of the power is provided by the machinery that carries the rider and bike to the top of the run. Bicycling should be a human-powered activity, or it is not bicycling to me.
Downshift
The act of shifting to a lower gear. In the case of derailer gearing, this means shifting to a larger rear sprocket, or a smaller chainwheel in front.
Drag Brake
A brake that can be set so that it will stay on even when the rider lets go of the control lever. This is usually a drum brake operated by a friction-type shift lever. Tandems are often equipped with a drag brake when they are to be used for touring in mountainous terrain. Descending with a heavily-laden tandem using only rim brakes can cause the rims and tires to overheat, leading to blowouts.
See my article on Tandem Brakes.
Draft
To follow another cyclist (or motor vehicle) so closely that the leading vehicle takes the brunt of the wind resistance, and acts as a windbreak for the drafting cyclist.
Since air resistance is the major limitation on bicycle speed, many of the tactics used in bicycle racing are based on exploiting this effect.
Drainpipe
British term for a tandem's Keel tube.
Draisine
Before the invention of the bicycle, a German nobleman named von Drais invented the "draisine" which is like a bicycle without pedals. The rider would use his feet to push along the ground. The draisine walking enhancer, permitting the user to cover more ground with each stride, and to coast down hills.
When Pierre Lallement added pedals to a draisine in the 1850s, the bicycle was born.
Draisines are still made for small children, intended as a transitional vehicle between a tricycle and a bicycle, but I don't recommend buying these, because you can acheive the same effect by unscrewing the pedals from a real bicycle.
See my article on Teaching Children to Ride.
Driver
The part of an internal-geared hub or coaster brake that the sprocket attaches to, either by threads or splines.
See also threaded driver.
Drivetrain
The parts of a bicycle which have to do with generating forward motion. These include the pedals, cranks, chainwheels, bottom bracket, chain, derailers, rear sprocket(s) and rear hub.
The drivetrain area of a frame consists of those parts of the frame that are directly stressed by the drive train parts, specifically the chainstays, down tube, and seat tube.
Drop
- Frame geometry: the difference between the height of the fork ends and the height of the bottom bracket. Smaller drop = a higher bottom bracket. This dimension is often preferred to the bottom-bracket height dimension, because it is the same whatever tires are installed on the bicycle.
A bicycle with a shorter drop (higher bottom bracket) will be less at risk of striking a pedal on the ground during high-speed cornering or obstacle jumping.
A bicycle with a longer drop (lower bottom bracket) will be slightly faster, and easier to mount/dismount. - Handlebars: the vertical dimension of a drop handlebar, from the horizontal part to the level of the drops.
Drops
The lower parts of a drop handlebar, the area below the brake levers.
Drop Bolt
An offset mounting bolt, to allow a short-reach brake caliper to be used where a long-reach one would otherwise be required. See my Home Made Drop Bolts article.
Drop Handlebar
A drop handlebar is one in which the middle of the bar is the highest point, or nearly. Most bicycles built for fast or long-distance riding have drop handlebars, which provide a range of different grip positions, allowing the rider to change positions for variety and to accommodate different road/wind conditions.
The most common style of drop handlebar is the "Mæs" bend. Variations include the "randonneur" and "anatomic" bends.
 Mæs |
 Randonneur |
|---|
The main advantage of drop handlebars is that they offer several different hand positions. For longer rides, the ability to change positions is very desirable. Riding for a long time in any one position tends to be uncomfortable.
People who think they don't like drop handlebars are often actually objecting to the position of the bars on the drop-bar bikes they have tried.
Bikes with drop bars often have the bars mounted rather low and far forward, so that the rider has to lean forward quite a lot to reach the bars, especially the lower "drop " position. If these people tried a bike where the drop bars were placed higher, and closer to the saddle, they might find they really liked them.
I have an article on this topic, called "Hands Up."
Most newer drop handlebars come in either single-groove or double-groove versions, with grooves along the upper section to acommodate brake (and shift) cables running under the handlebar tape.
These grooves are totally unnecessary. Indeed, the double-groove variety is often rather uncomfortable due to the rear groove's causing sharp ridges against the rider's hands.
Dropout
A type of forkend that allows the rear wheel to be removed without derailing the chain first.
Track and BMX bicycles do not have rear dropouts; they use fork ends that open to the rear.
A current fad has led to the revival of this inferior forkend style for single speed bikes.
Rear dropouts come in two styles:
- Horizontal dropouts have a longish slot for the rear axle to fit into, which runs more-or-less horizontally along the dropout. They permit the wheel to be placed in various positions front to rear. Horizontal dropouts are necessary for bicycles which don't have derailers, because the axle must be moveable to adjust the chain tension. With horizontal dropouts, it is possible to mis-align the wheel in the frame if it is installed carelessly. The axle nuts or quick-release must be tightened quite securely, or the chain tension may pull the axle askew.
- Vertical dropouts have a vertical notch for the axle to go up into, and the axle's position is not adjustable. With vertical dropouts, the axle cannot be pulled out of position, even if it is not properly secured. Vertical dropouts are generally intended for use with derailer gearing, and do not permit any adjustment of the position of the rear wheel, so there's no way to regulate chain tension if you don't have a derailer or pulley type chain tensioner.
A few single-speed or internal-hub gear bikes use vertical dropouts with an eccentric bottom bracket to permit chain tension adjustment.
White Industries makes a special hub with an eccentric axle, also to permit vertical dropouts to be used with a straight chain run.
On derailer-equipped bicycles, the rear derailer is attached to the right rear dropout, either directly to a hanger that is part of the drop out, or by way of an adaptor claw.
Dropout spacing varies among different styles of bicycles
| Forged Dropouts | |||
|---|---|---|---|
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| Horizontal Dropout Campagnolo 1010 |
Horizontal Dropout Short |
Semi-Vertical Dropout | Vertical Dropout |
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| Stamped Dropouts | Investment Cast | ||
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| With Hanger | Without Hanger | Raleigh 3-speed | Track Forkend Not a dropout! |
Drum Brake
A drum brake is a hand-operated brake which is built into, or attached to the hub of a wheel, with shoes that press against the inside of a cylindrical drum.
The drum may be the inside of an oversized hub shell, or may be a separate unit which screws on to the side of the hub, by threads like those to which freewheels attach.
Drum brakes are common on automobiles and motorcycles, but fairly rare on bicycles, mainly due to their weight. The greatest advantage of a drum brake is that it is unaffected by rain. Drum brakes are commonly used as drag brakes on tandems. Also see the articles on Drum Brakes and on Tandem Brakes.
Dry Rot
"Dry rot" is a fungus that infects cellulose-based materials: wood, paper, cotton and the like.
Sometimes people speak of bicycle tires as if they suffer from dry rot, but this is not generally correct. (The exception would be for cotton-cord tires, but those pretty much disappeared by the mid 1960s, at least as far as clinchers are concerned.)
What people commonly call "dry rot" is a deterioration of the rubber, usually on the sidewalls. This is particularly common with gumwall tires that have been exposed to ozone damage. (A common cause of this is storing a bicycle near a household furnace. The brush-type motors on such furnaces often create sparks, which in turn create ozone.)
This type of damage is ugly, but not structurally significant, as long as the cords (fabric) of the tire are intact.
Generally, if a tire isn't lumpy/misshapen when inflated, and has not had the tread area worn too thin, there is no reason to replace it, no matter how ugly the sidewalls get.
D.S., N.D.S.
For some obscure reason, some writers on bicycle matters seem to have a problem with the terms "right" and "left."
Instead of using these easily understood common English words, they have invented the terms "drive-side" for "right" and "non-drive-side" for left. (This relates to the fact that the chain drive is on the right side.)
As if this silly jargon were't confusing enough, they sometimes further muddy the waters by abbreviating these phrases as "D.S." and "N.D.S."
Dual-Pivot
A type of sidepull brake caliper. The dual-pivot design was originated by Altenburger in the 1960's, and popularized by Shimano in the 1990's.
The main feature of dual-pivot brakes is that they are easier to keep centered, due to the way the arms are linked together. They can have more mechanical advantage (and a resulting rest position closer to the rim) than conventional sidepulls. Newer designs permit fine tuning the centering of the arms by simply turning a screw.
The principal disadvantage of dual-pivot brakes is that they don't track imperfect rims as well as single-pivot sidepulls, possibly causing pulsating braking.
Thanks to Mark McMaster for his help with this entry.
DT ®
Swiss DT is the leading manufacturer of spokes. When DT spokes first became available in the U.S. market in the late 1970's, they revolutionized wheel building. Although stainless spokes had been available previously, the quality of the threading on DT spokes and nipples was quite a lot better than that of brands that had previously been available, allowing wheels to be built at considerably higher spoke tensions than had previously been possible.
"DT" stands for "Drahtwerke Tréfilerie." "Drahtwerke" means "wire works" in German; Tréfilerie means the same thing in French.
Dual Suspension
Refers to a bicycle with suspension for both wheels.
Dunlop
John Boyd Dunlop was born in Ayreshire, Scotland, in 1840. He studied veterinary science at the University of Edinburgh. In 1888,he invented the pneumatic tire, probably the most revolutionary and important invention to come out of the bicycle industry. J. K. Starley's chain-driven "safety" bicycle had been invented three years earlier, but was not fully practical due to the harsh ride of the smaller wheels with solid tires. With Dunlop's pneumatic tire, the modern bicycle was basically complete. No development in bicycle technology since then has been more than a minor refinement on the work of Starley and Dunlop.
Because an earlier patent for an inflatable tire had been taken out in France, his 1888 patent was invalid in Scotland, so he moved to Belfast, Northern Ireland, and started manufacturing tires in 1890.
The Woods valve is also sometimes referred to as a "Dunlop" valve.
The Dunlop tire company which he started still exists, but stopped making bicycle tires in the 1960's. This caused a crisis among cyclists for a couple of years, because Dunlop bicycle tires were incontestibly the finest available. The Dunlop "HPRR" (High Pressure Road Racing) tire was the high-performance "clincher"
Dura Ace
Shimano's top-of-the-line parts group for road racing bikes. See Shimano Models and Buzzwords.
There are interchangeability issues with older Dura-Ace parts, and I have an article on Dura-Ace interchangeability.
Duralumin, Dural
Duralumin is a trade mark name for an early popular structural aluminium (aluminum) alloy, and 'dural' is slang for it. Dural has a poor corrosion resistance, and (I hope) isn't used much for cycle parts nowadays. It needs a paint or lacquer finish if used out of doors in dirty conditions. (Thanks to Mark Irving)
Dustcap
- A thin metal, plastic or rubber shield that covers the bearing balls of a conventional cup-and-cone hub.
- A plastic or metal cap that screws or snaps into the extactor threads of a cotterless crank.
Dyna Drive ®
In the early '80's, Shimano introduced a special crank/pedal set, which used much larger diameter threading where the pedal screwed into the crank. This allowed the bearing to be built into the inside of the pedal thread, eliminating the need for a pedal axle. The purposwas to improve the biomechanics of the pedal by placing the bottom of the foot below the pedal axis.
The threading chosen was 1" x 24 tpi, same as a standard 1 inch headset, except that the left side was a left thread.
This was rather a good idea, but never caught on.
Dynamo
British term for generator. Technically, the term "generator" is preferred, because "dynamo" primarily refers to a generator of direct current, while bicycle generators all produce alternating current.
