Shock Value: The Glossary

The first entry in our Shock Value education series is this extensive glossary. We hope it will serve as a way to demystify the jargon in the stories and reviews you’ll read here at The Radavist. But we also think it functions as a standalone educational tool. There are a lot of systems and concepts at work in our suspension. We’re not just here to explain how they affect your ride but also how they function. So, we invite you to take a leisurely scroll through. You may find it will deepen your understanding of what makes your suspension tick and how to make it tick better. Or, simply use your browser’s search function to find the word you’re looking for.

Shock Value is presented by RockShox

Active

If rear suspension is described as “active,” that means it continues to react to bumpy terrain, even if the rider is pedaling or braking. This is a standout characteristic because, on some bikes, rear suspension motion can be inhibited while pedaling or braking. But depending on terrain and rider preference, <i>less</i> active suspension may actually be ideal.
See also: Anti-squat and anti-rise

Aftermarket

Components that did not come specced as original equipment on a new complete bike. The opposite of OEM.

Air can

The main pressurized chamber, specifically referring to a rear shock. Usually, the larger-diameter part of the shock is the outer surface of its air can.

Air spring

The pressurized chamber that provides support in an air-sprung fork or shock. Air springs are generally a more common alternative to metal coil springs. They are also usually lighter weight and may be more supportive than coil springs, but may not be as sensitive to bumps. This is why some bikes built primarily for downhill performance still use metal coil springs.
See also: Spring curve

Anti-rise

A measure of how little or how much a bike’s rear suspension will tend to extend (or “rise”) under rear-braking force. This is a function of linkage and brake-mount design, but also body position and center of gravity. It is not a concrete, easily quantifiable measurement, but it is usually expressed as a percentage. An anti-rise value of under 100% means the rear suspension is more likely to extend while braking, possibly compromising downhill geometry, but also remaining more active. A value over 100% means it is more likely to compress while braking, optimizing downhill geometry but possibly resulting in less active suspension.
See also: Brake-jack

Anti-squat

A measure of how little or how much a bike’s rear suspension will tend to compress (or “squat”) under pedaling force. This is a function of linkage design, but also drivetrain configuration, gear ratio, and center of gravity. It is not a concrete, easily quantifiable measurement, but it is usually expressed as a percentage. An anti-squat value of under 100% means that pedaling force may be more likely to compress the suspension. This can potentially cost you energy, but the suspension may have an easier time remaining active under pedaling force. An anti-squat value of over 100% means that pedaling force is more likely to extend the suspension. This can potentially save you energy, but the suspension may be less active.
See also: Pedal kickback

Axle path

The shape of the imaginary line drawn by a rear axle as the rear suspension moves through its stroke. Most published axle-path charts are exaggerated to make the relatively minuscule horizontal movement more clear.

Axle-to-crown

Measured parallel to the fork, this is the distance from the center of the front axle up to the base of the fork crown where the lower headset bearing seats. Axle-to-crown varies based on suspension travel, wheel size, and fork design.

Balanced

Referring to a bike whose front and rear suspension characteristics feel matched in a given scenario. Often, a bike’s rear suspension may feel more sluggish than the front, or the front may feel less supportive than the rear. Proper setup can usually solve these issues.

Bob

A catch-all term for unwanted rear-suspension movement while pedaling. Some suspension bob is directly caused by drivetrain force interacting with the suspension linkage, when a bike’s design has particularly high or particularly low anti-squat. But bob can also be caused by a rider’s natural pedaling motion as their weight transfers from saddle to pedal and back. Or as they bounce their bodies during forceful pedaling.
See also: Anti-squat

Bottom-out

When front or rear suspension reaches the end of its travel. There is usually a simple rubber bumper to prevent component damage caused by harsh bottom-out. Sometimes there are measures at play to further soften bottom out. Using volume spacers in an air shock, or a progressive spring on a coil shock may help soften or prevent harsh bottom-outs. Or, some suspension designs have higher-tech built-in measures to manage bottom-outs. Note that the average rider might occasionally bottom out their suspension, even with a proper setup.Tuning suspension to never ever bottom out will result in a harsher ride and poorer traction.

Brake-jack

A misleading term, brake jack is related to anti-rise. It is shorthand for rear suspension not functioning properly under braking force, but there is no universal consensus on what it means. Some say it results from high anti-rise values, some say it results from low anti-rise values.
See also: Anti-rise

Bushings

The low-friction surfaces (usually polyurethane) that support a fork or shock’s internal sliding surfaces. Inside a fork and rear shock, these are the rings which the stanchions slide through during compression and rebound. But also, most rear shock eyelets rotate around replaceable bushings, though some use ball or needle bearings.
See also: Eyelet

Capable

When used in discussing suspension or a suspended bike, this usually refers to its ability to absorb large impacts, as well as to maintain traction, speed and stability on rough terrain.

Cavitation

The expansion and subsequent collapse of air bubbles in damper fluid as a shock or fork compresses and rebounds. This leads to inconsistent damper performance and potential structural damage inside the damper. Cavitation may be caused by air leaking into the damper or a malfunctioning internal floating piston. It can usually be prevented by regular professional damper service.
See also: Hysterisis

Center of mass

Often used when calculating anti-squat and anti-rise, the center of mass is the midpoint of combined rider weight and bike weight.

Chain growth

This concept refers to the “driving” portion of the chain. It’s the top portion that extends from where the chain leaves the top of the rear cog forward to where it meets the top of the front chainring. At various points along a full-suspension bike’s rear travel, this distance may lengthen, shorten, or stay (mostly) the same. Positive chain growth is associated with high anti-squat values, and negative chain-growth is associated with low anti-squat values.
See also: Anti-squat and Pedal kickback

Check valve / Return valve

A simple one-way valve that allows oil to flow freely back through a piston inside a damper.

Circuit

A common term for the paths that oil follows when flowing through a damper. Although the paths are actually a series of three-dimensional shapes, they look like an electronic circuit when viewed in cross-section.
See also: Damper

Compression damping

The system of valves and fluid that manages a fork or shock’s shaft speed during compression. Nearly all forks and shocks feature a mechanism that provides compression damping, though it is not always externally adjustable. Heavier-weight or more aggressive riders tend to want heavier / more compression damping to offer support and keep them high in the travel, while lighter, more conservative riders may want lighter / less compression to keep the suspension sensitive.
See also: High-speed damping, Low-speed damping

Cross-talk

Unwanted interference between one damper circuit and another. For example, in a speed-sensitive damper, slowing down low-speed compression damping could potentially also slow down high-speed compression damping. Many advanced damping systems boast “independent circuits” to limit cross-talk.
See also: High-speed damping, Low-speed damping

Crown

The structure that joins a suspension fork’s steerer tube to its legs.

Dampening

This word has nothing to do with suspension. It only means “to make damp,” and is often confused with the word, “damping.”

Damping

The systems inside a fork or shock that control shaft speed during compression and rebound to balance support, control, and traction. As suspension moves, oil is forced from one chamber to another and back again. It moves through valves of various sizes and designs to allow for optimal suspension movement in a variety of scenarios. “More” or “heavier” or “slower” damping means the damper is doing more to slow down shaft speed, while “less” or “lighter” or “faster” damping means it is doing less to slow down shaft speed. The right damping settings for you depend on your spring rate, body weight, bike design, terrain, and personal preference.

Damper

The assembly inside a fork or rear shock that provides compression and rebound damping. In some European regions, “damper” is also a name for the entire rear shock.

Damper fluid

The oil that is cycled back and forth through a damper.

Damper shaft

The rod that pushes a damper piston back and forth through the damper fluid. The damper shaft takes up oil volume as it enters the damper body, which creates the need for an internal floating piston, bladder, or a simple pocket of air to take up the extra volume.
See also: Internal floating piston

Dropout

The part of a fork or frame that connects to the wheel’s axle.

Dual-crown

A type of suspension fork that supports its legs with two structures, one below the bike frame’s head tube and one above it. Dual-crown forks are used almost exclusively on gravity-focused bikes like those built for downhill racing.

Dual short link

A generic term for a family of rear suspension designs that include VPP, DW Link or CBF. Each of these designs is different, but they all connect a frame’s front triangle and rear triangle via two short links. A frame designer might choose a dual-short-link design for its effect on pedaling and braking characteristics.

Efficient

When referring to a full-suspension bike, this usually means the energy being put into the pedals does not feel like it is being absorbed in the shock. But it does not necessarily mean that the suspension does not move while pedaling. Suspension that is able to absorb uneven terrain while pedaling will add efficiency by maintaining the body’s momentum.

Eyelet

The mounting hole on one end of a rear shock. Some shocks have an eyelet on both ends, other shocks have an eyelet on just one end and a trunnion mount on the other end.
See also: Trunnion

Eye-to-eye

The distance between the center of one eyelet and the center of the opposite eyelet or trunnion mount on a fully extended rear shock.

Factory tune

Also called OEM tune, this refers to the specific “settings” inside the rear shock specced on a given bike. These settings are requested by the bike brand to suit a particular full suspension bike, and that brand’s intentions for it. This includes heavier or lighter damping or larger or smaller air spring volumes. When replacing a rear shock, it is often recommended to replace it with one that has been given the appropriate factory tune.

Flex-stay

An approach to full-suspension bikes where, instead of being handled by a bearing or bushing, the motion of one or more frame members is handled simply by material flex. Most often, this is near the rear dropout, where there is not much motion. It is also most common on light-duty or short-travel bikes.

Flexy

A term that usually refers to a bike’s or fork’s tendency to twist or flex laterally under pedaling, turning, or other load. It does not refer to vertical suspension motion.

Flip chip

A special structure around a pivot point or shock mount that allows for subtle changes in geometry or suspension behavior on a full suspension bike. Some flip chips are designed specifically to accommodate different rear wheel sizes while simultaneously optimizing frame geometry

Fork offset

The distance, measured perpendicular to a fork’s steering axis, between the center of the steerer tube and center of the stanchion. On most bikes made after 2019, forks meant for 29” wheels have 42 – 44 mm offsets and forks meant for 27.5” wheels have 36-38 mm offsets

Four-bar

A generic term for a family of traditional rear suspension designs that consist of the chainstay, the seatstay, and the rocker link, and the seat tube. A Horst Link is a common four-bar design.

Harsh

A term used when a bike’s suspension is not responsive enough to small or high-speed impacts. If harshness did not result from improper setup, it may be caused by things like too much high-speed compression damping in a factory tune, a poorly optimized negative air spring, or rear-linkage kinematics that do not respond well to initial small bumps.

High in its travel

A term used when suspension is supportive under pushing, pedaling, pumping or braking loads, but can still keep extra travel on reserve for sudden bumps. This may be a good thing or a bad thing depending on whether talking about front suspension, rear suspension, uphill or downhill. For instance, it is generally desirable on descents for front suspension to stay high in its travel, but bad for rear suspension.

High pivot

A type of rear suspension linkage where the main pivot (the pivot the rear wheel primarily arches around) is a few inches higher than on a traditional linkage. This angles the axle path rearward, offering better stability and bump sensitivity at speed. High pivot bikes require the chain to run through an idler pulley near the raised pivot.

High-speed damping

Note that this image is only an abstract representation of how a speed-sensitive damper functions.

Most high-end dampers are designed to allow a fork or shock to behave differently depending on shaft speed. Usually, these are not independently adjustable. If there is only one compression damping adjustment, it usually only controls low-speed compression. But some high-end suspension components do offer independent high- and low-speed compression and / or rebound adjustment.
- High-speed compression damping is the system that manages fork or shock motion during rapid compressions like tracking over sharp bumps or absorbing large impacts. The goal is to allow the suspension to react quickly, but not blow through too much of its travel too quickly. Some riders prefer light high-speed compression damping because it makes for better sensitivity, but aggressive riders may sacrifice some of that to keep their suspension from being overwhelmed.

- High-speed rebound damping is the system that manages fork or shock motion while it is rebounding from deep in its travel, where rebound forces are greatest and shaft speeds are highest. The goal is to allow the suspension to quickly return from being near bottom-out so it can continue tracking the ground, but not so quickly that it bucks or destabilizes the rider. Very few suspension components allow the rider to adjust high-speed rebound damping independent from low-speed rebound damping. And some lower-priced suspension components will not even have a high-speed circuit in their rebound damper. Most riders set their high-speed rebound similarly to their low-speed rebound.

Horst link

A very common four-bar linkage design that features a pivot along the chainstay near the dropout. Although frame designers have a lot of freedom to tune the specific suspension behavior they want, Horst-link bikes are often praised for their ability to prevent braking force from inhibiting suspension motion.

Hysteresis

When this term is applied to suspension, it refers to a lag in a damper’s ability to “keep up” with suspension movement. It may stand out as a noticeable gap in the damping. This can be caused by problems like cavitation or the wrong pressure in the internal floating piston.
See also: Cavitation

Instant center

The point (or series of points) around which the rear wheel arches throughout the suspension travel. On a single-pivot bike, the instant center is always the center of the main pivot. But on Horst link, dual-short-link, or other complex designs, the instant center is an imaginary point in space. Sometimes called a “floating” or “virtual” point, these imaginary points will change location throughout the suspension travel.

Internal Floating Piston / IFP

A sliding of “floating” piston at end of many fork or shock dampers that accommodates for the damper fluid displaced by the damper shaft as it enters the system. Most IFP designs use pressurized air, but some use a coil spring. Alternative methods for accommodating that displacement are open-bath dampers or dampers partially contained by a flexible bladder.

Inverted fork

A design that puts the stanchions at the bottom, not the top of the fork. Inverted forks may be lighter because they don’t use as much material as a traditional fork. But they also tend to be more flexy.

Kinematics

The general term for the motion of a rear-suspension frame. This encompases axle path, leverage rate, anti-squat, anti-rise, etc.

Leverage ratio / Leverage rate

Usually expressed in a single number, this represents the ratio of the total rear wheel travel to the total shock stroke. If a bike with 125mm of rear travel is built around a shock with 50 mm of stroke, that bike has an overall leverage ratio of 2.5. But that is only an average. The leverage ratio will change throughout the travel, and that change is expressed as a “leverage curve.”

Leverage curve

The leverage ratio does not stay constant throughout a rear suspension’s entire stroke. So, leverage curves are a way to track how a leverage rate changes as the suspension moves. If you have some knowledge of the shock’s spring curve, knowing its leverage curve can tell you how supportive vs how sensitive your suspension will be at various points in the travel.

Linear

When used as a general term for suspension behavior, “linear” means a fork or shock does not significantly increase its support throughout the travel, but instead remains constant. This can be good for absorbing large bumps, but may result in a sluggish feel. Alternatively, “linear” may refer to a rear linkage’s leverage curve that does not significantly increase support throughout the travel. But what that means for ride feel depends on what spring is used in the shock, which itself may be more linear or more progressive.

Linkage

The term used for the physical frame components, not including the shock, that make up a bike’s rear suspension assembly.

Lockout

An outdated term for the lever or switch featured on some forks and shocks that instantly firm up the damping, usually to help when climbing on relatively smooth surfaces. Most modern “lockouts” don’t totally eliminate flow inside a damper. Instead, they just significantly restrict it. That’s why many suspension brands use words like “firm mode” or “climb switch” instead of “lockout.” Also, as frame geometry and suspension design improves, the need for these levers is not what it used to be. Many climbs, especially technical ones, are more efficient without these switches engaged.

Lowers

The lower portion of suspension fork legs. These are the external legs that slide over the stanchions as suspension moves.

Low-speed damping

Note that this image is only an abstract representation of how a speed-sensitive damper functions.

Most high-end dampers are designed to allow a fork or shock to behave differently depending on shaft speed. Usually, these are not independently adjustable. If there is only one rebound damping adjustment, it usually only controls low-speed rebound. But some high-end suspension components do offer independent high- and low-speed compression and / or rebound adjustment.
- Low-Speed Compression Damping is the system that manages fork or shock motion during slow compressions like pedaling or braking. The goal is to keep the rider supported when they are putting even downward force on the bike. Low-speed compression is not always externally adjustable, but nearly every fork or shock has some mechanism to provide it. Some suspension components offer independant adjustment of high- and low-speed compression damping, but if there is only one external adjustment, it will be for low-speed compression damping.

- Low-Speed Rebound Damping is the system that manages fork or shock motion during rebound. The goal is to allow the suspension to return from being near bottom-out quickly so it can keep tracking the ground, but not so quickly that it bucks or destabilizes the rider. On suspension with speed-sensitive rebound damping, low-speed rebound damping primarily affects return speed in the earlier portion of the stroke when return forces are not particularly high. But many rebound-dampers are not speed-sensitive, and both shallow and deep-stroke rebound are controlled by the low-speed circuit.

Mid-stroke

The segment of suspension travel that is just past sag, but well before bottom-out. Often, you’ll hear praise for “supportive mid-stroke,” which means that a fork or shock does not excessively wallow past its sag point under loads like pedaling, pumping or turning.

Negative air spring

A small pressurized chamber inside most air-sprung forks and rear shocks that actually creates a compressing force, pushing in the opposite direction to the main or “positive” air spring. It helps initial bumps overcome an air spring’s natural resistance to start moving. Most modern negative air springs gain pressure naturally while you compress and release your suspension, but some allow you to change their volume to augment suspension feel.

OEM

Technically meaning “original equipment manufacturer,” this generally refers to components that were originally specced on a complete bike out of the box, not components purchased aftermarket. Some suspension components (especially lower-priced ones) are manufactured in configurations that areexclusively available as OEM product, and only their higher-end counterparts are available aftermarket.

Overdamped

A trait of some suspension components to feel too slow on compression, rebound, or both. Even adjustable dampers sometimes can not be adjusted to offer quick enough shaft speed for some riders. This problem tends to be more common for lighter-weight riders.

Oversprung

A trait of a suspension component whose spring is too stiff. On an air-sprung fork or shock, the solution is simply to decrease pressure. On coil-sprung suspension, the coil itself needs to be replaced.

Pack-up

A problem where a fork or shock is not rebounding quickly enough to properly absorb successive bumps. This leads to a harsh feel because the suspension is stuck deeper into its travel than is ideal, where the spring force is higher and there is less travel available. It also can compromise geometry.

Pedal kickback

A negative side-effect of some full suspension bikes where compressing the suspension pulls back on the pedals. Shallow suspension motion while traveling at reasonable speed will rarely cause pedal kickback. Pedal kickback is usually most noticeable when a relatively large impact occurs while the rider is traveling at a relatively slow speed. This is not a common combination, but it does happen and can cause suspension to feel harsh. Factors that play a role in pedal kickback are suspension kinematics, gear ratio, and hub engagement speed.

Piggyback / Reservoir

An external structure housing damping components commonly featured on longer-travel rear shocks. A suspension manufacturer might use a piggy-back shock to offer more room, either for more complex damping systems or to separate compression damping circuits for less cross-talk. It also allows a shock to hold more damper fluid, which can offer better heat management.

Planted

A term often used for bikes with an aptitude for hugging the ground, even in rough terrain.

Playful

A term often used for bikes that are more maneuverable and responsive. Relating to suspension, this usually means a bike stays supportive when a rider puts their weight into it for a turn or to pump or to jump.

Preload

On an air shock or fork, this is how much air pressure is in the air spring when the bike is at rest. On a coil shock or fork, this is how much the spring has been compressed to achieve the preferred sag during setup. It should be noted that coils are designed to have very little preload. Instead, various spring rates are manufactured to suit your weight and your bike. The spring should be swapped for one with a higher spring rate if you need to use excessive preload.

Progressive

A term usually used to describe front or rear suspension that provides increasing support as it goes through its travel. Progressive suspension tends to offer good small-bump sensitivity, and will resist harsh bottom-outs. But depending on the leverage curve, it may lack mid-stroke support and may make it difficult to use all the travel. On rear suspension, progressivity is a function of both leverage curve and spring curve. On front suspension, it is just a function of spring curve.

Pump

The action of pushing down on a bike to maintain speed through a sharp turn or over a hump in the trail. Similar to the action of pumping up a tire. There, of course, are also shock pumps designed specifically to be accurate and work with high pressures.

Ramp-up

A relatively sudden increase in support at some point in a leverage curve or spring curve. Sometimes there is ramp-up late in the stroke to prevent bottom-out. Sometimes there is ramp-up early in the stroke to reserve the first portion for small-bump sensitivity

Rebound damping

The system that manages a fork or shock’s shaft speed during rebound. By limiting the flow of damper fluid, rebound damping prevents a shock or fork from returning too quickly and bucking or destabilizing the rider. As you increase spring preload to suit your weight, it is recommended to increase rebound damping. It is almost always externally adjustable. Some suspension offers independent high and low-speed rebound damping, but if there is only one knob, it adjusts low-speed rebound damping. See also: High-speed rebound damping

Sag

The amount of front or rear travel you use up simply by sitting or standing on your bike. When referring to the setup process, sag is usually measured on flat ground while out of the saddle with your weight somewhat even between pedals and grips.

Shaft speed

The speed at which a fork or shock is compressing or rebounding. This term is not necessarily related to the speed at which the rider is traveling.

Shim stack

Most speed-sensitive damping involves forcing damper fluid through something called a shim stack when shaft speed is too fast for the primary low-speed port to handle it all. Shims are flexible washers that cover a series of holes aranged in a circle around the damper shaft, and the shims flex out of the way to let oil through once it’s moving fast enough. Shims are often stacked in varying sizes and shapes to achieve the manufacturer’s desired performance. Custom suspension tuning shops might change these shims to suit a rider’s unique demands.

Single-crown

A fork configuration (more common than dual-crown) where the stanchions are connected to the steerer tube by one structure below the head tube

Single pivot

A suspension frame design that arches the rear wheel around one fixed pivot point. Some single-pivot frames compress the shock through a simple one-piece swingarm. But other single-pivot frames compress the shock through a more complex linkage. These “linkage-driven single-pivot” designs still have a simple arched axle path, but frame designers have more control over their leverage curve.

Speed-sensitive damping

A shock or fork’s capability to react differently to slow shaft speeds than to fast shaft speeds. Usually, this is achieved by a secondary valve that opens when damper fluid is moving too fast through the primary port for it to handle it. Sometimes, these ports can be independently adjusted, but adjustment is not necessary for damping to be speed-sensitive.
See also: High-speed rebound damping and High-speed compression damping.

Spring curve

A representation of the increase in support a spring offers. The rate of increase on a coil spring is almost entirely constant, while an air spring’s support tends to increase more steeply late in the stroke. This effect is greater as air volume decreases.

Spring rate

The amount of weight it takes to compress a spring a given amount. On coil springs, it is usually measured in pounds per inch.

Sprung mass

The parts of the bike or the rider that are supported by a bike’s suspension. On a front suspension bike, your arms and your handlebars are sprung mass, while your front wheel and brake caliper are unsprung mass. Adding sprung mass has less of a negative impact on suspension performance than adding unsprung mass because sprung mass is less affected by bumps in the terrain. In fact, adding sprung mass can often make a bike more stable.
See also: Unsprung mass

Stanchion

The smooth tubes that make up a traditional suspension fork’s upper legs, which slide into the lower legs during compression.

Stroke length

Usually used when talking about rear suspension, stroke length is the total amount a shock is able to compress. This differs from actual wheel travel because of the leverage created by the linkage. Full suspension bikes are designed to fit a shock with a particular eye-to-eye and stroke length, but occasionally, a frame can be designed to accommodate small differences in total stroke length to offer increased or decreased wheel travel.

Supportive

A term for suspension that does not sink when you don’t want it to, specifically under smooth loads like pedaling, pumping, or braking. This can be thanks to optimization of damper performance, leverage curve, and/or spring curve, which add support without sacrificing traction or small-bump performance

Technical

Terrain that is not just bumpy, but also unpredictable due to tight turns or sudden steep climbs and descents

Traction

This is the ability for a tire to grip the ground without sliding. But it also refers to the wheel’s ability to “track” along an uneven surface, which relates directly to suspension. Suspension allows the wheel to move up as it hits bumps, and the impact is not disrupting your body’s momentum. When those impacts are unsuspended, they are more likely to unweight the wheel and cause loss of traction. Also, after a wheel hits a bump, the suspension allows it to return to the ground quickly so it can maintain grip, without bouncing or skipping.

Trail

The horizontal distance between where the front tire touches the ground, and the point in front of it where an imaginary line through the steering axis intersects the ground. Trail is determined by several factors including head tube angle, wheel size, and fork offset. But it changes as a suspension fork moves through its travel. Put simply, shorter trail measurements tend to make a bike easier to control at slow speeds and less stable at high speeds, and longer trail measurements tend to make a bike harder to control at slow speeds but more stable at high speeds.

Travel

The amount that a wheel moves on a front- or rear-suspended bike, measured along the axle path.

Trunnion

A rear-shock mounting method used on one end of some models. Instead of through a traditional eyelet, bolts are threaded directly into the shock body itself. This allows frame manufacturers to fit a longer shock into a smaller space. But it can translate more frame flex directly into the shock, which some say reduces shock longevity.

Undamped

A type of front or rear suspension that consists of only a spring, with no hydraulic damper to control the motion. Inexpensive bikes are often undamped to save cost, but it can also be done on the high-end in specialty situations to achieve ultimate simplicity or light weight.

Underdamped

A trait of some suspension components to feel too fast on compression, rebound, or both. Even adjustable dampers sometimes can not be adjusted to offer slow enough shaft speed for some riders. This problem tends to be more common on more aggressive or heavier-weight riders who tend to require more or “heavier” damping.

Undersprung

A trait of a suspension component whose spring is too soft. On an air-sprung fork or shock, the solution is simply to increase pressure. On coil-sprung suspension, if the desired spring rate can’t be achieved with a reasonable amount of preload, the coil itself needs to be replaced with a heavier spring.

Unsprung mass

The parts of the bike and rider that are not supported by a bike’s suspension. On a front suspension bike, your front wheel and brake caliper are unsprung mass, while your arms and your handlebars are sprung mass. Adding unsprung mass can have a negative impact on ride quality, regardless of suspension, because it is impacted directly by uneven terrain.
See also: Sprung mass

Volume spacer / Volume reducer

A specially designed plastic object inserted into a fork or rear shock’s air spring to reduce overall air volume, thereby augmenting the spring curve to increase bottom-out resistance. Many bikes will come with some amount of volume reduction chosen by the designer.
See also: Spring curve

Wiper seal / Dust wiper

The outward-most rubber seals on a fork or rear shock that is the first line of defense against contamination. Dust wipers are often easily user-serviceable.