Motorcycle Suspension Terms Glossary

Welcome to my Motorcycle Suspension Terms Glossary.

I have been thinking a lot recently about swapping out the stock front-end of “Cal” for a springer front-end.  You know when sometimes you see a custom-bike on the road or even a factory-bike and you just like the “look.”  Well, that is what the springer front-end has always been for me – a “look” that I just inherently like and have always wanted.
Motorcycle Suspension Terms Glossary

When I built my first Harley Davidson Shovelhead a good 20 years ago, I didn’t have the money to do everything I wanted.  I am not saying that I am rolling in it now by any means; but I am working A LOT smarter not harder during my restorations. 

For example, I do a lot of my own rust removal and custom painting – really all my blog posts are geared at the DIY motorcycle repair person who is on a budget.  The first shovelhead was simply a chrome monster – I can admit that now, while “Cal” is more the product of elbow-grease and love.

Anyways, total digression there, but the point is that I thought I would share some lingo regarding motorcycle suspension.  There are a lot of terms that go along with the simple process of dampening bumps in the road, and it is fun to know all the terminology.  The sortable and searchable table below is a combinations of resources I have found around the web.  Check the references below the table for original sources.

TermDefinition
ANTI-SQUAT RATIOA formula that calculates the relation between the drive sprocket, rear tire contact patch, swinging arm pivot height, and the chain force lines. In order to determine the rear suspension’s characteristic to squatting under acceleration.
AXLEThe spin axis of a wheel.
BASE-VALVEThe compression piston and valving that fits onto the compression bolt assembly.
BLADDERA closed-end, thick rubber, cylindrical shaped piece that contains the nitrogen gas in a rear shock. The bladder works like an extra cushion on HSC.
BOTTOMING or BOTTOMING OUTA riding situation whereby all the suspension travel is utilized.
BUMPERA taper shaped dense foam piece that fits on the shock shaft.
BUSHINGA bronze or plastic ring used as a load bearing surface in forks or shocks.
CENTER OF GRAVITY/MASS CENTERThe center point of the motorcycle’s mass. Normally located somewhere behind the cylinder and below the carburetor of a dirt bike.
CHASSISThe frame, swing arm, suspension, and wheels of a motorcycle.
CLEVISA fork shaped piece of aluminum used as the bottom mount for most shocks.
CLICKERSThe knobs or screws that control the LSC & LCR circuits of the forks or shock.
COMPRESSION BOLT ASSEMBLYA large diameter bolt that houses the low speed compression adjusting screw and the compression valve assembly.
COMPRESSION DAMPINGThe damping circuit that absorbs the energy of compression forces on the damper.
COUNTER STEERINGWhen the rider applies steering pressure in the opposite direction of the turn.
DAMPERA fluid chamber with a means of regulating the fluid flow to restrain the speed of the moving end of the damper during the compression or rebound strokes. A set of forks and a rear shock are considered dampers.
DAMPER ASSEMBLY The parts of a shock comprised of the clevis, shaft, bumper, piston, and shims.
DAMPER RODThe large diameter aluminum tube in the lower leg of telescopic forks.
DAMPER SPEEDThe relative speed in which the moving end of a damper compresses or rebounds. The two different speeds are high and low.
DAMPINGThe process of absorbing the energy of impacts transmitted through the forks or rear shock on the compression stroke, and the process of absorbing the energy of the spring on the rebound stroke.
DAMPING CIRCUITSThere are normally four damping circuits which affect the damper’s speed. There is both a low and high speed circuit for the compression and rebound strokes.
DAMPING ROD FORKA simple type of fork that utilizes a tube with holes in it to create compression and rebound damping, delivering an extremely progressive damping curve. 
DIVEDuring heavy braking the front fork will compress due to the weight transfer. The term "dive" refers to the horizontal movement of the bike.
FLICKINGThe action of putting the bike into a full lean position quickly.
FORK OIL LEVELThe level of oil within the fork as measured when fully compressed without the spring installed. It is used in tuning the amount of air contained inside the fork.
FREE SAGThe amount the bike settles under its own weight.
FRONT END DIVINGThis is what happens when the front forks compress quickly. It usually occurs when braking for turns.
GEOMETRYThe term geometry refers here to a motorcycles overall geometry. A motorcycles geometry is a combination of rake, trail, etc.
HANDLINGThe quality of response from the chassis of a motorcycle, while riding through a variety of obstacles like turns, jumps, hills, whoops and bumps.
HARSHNESSA word used to describe the quality of the damping.
HEAD SHAKINGA term that describes the high speed oscillation of the forks when braking for a bend at the end of a fast straight-away. Every motorcycle has a certain frequency band when it oscillates. This frequency can be tuned to a higher vehicle speed with a sacrifice in the bike’s ability to turn.
HIGH SIDINGA term that describes what happens when a bike falls to the outside of a turn.
HIGH-SPEED DAMPINGDamping to control fast vertical movements of suspension components caused by road characteristics such as square-edged bumps
HOPPINGWheel hopping is when the tire bounces up off the ground due to a reaction from a bump.
HSCHigh Speed Compression damping circuit is affected most when riding fast over square-edged bumps.
HSRHigh Speed Rebound damping is affected in the same riding circumstances as HSC.
KICKINGA word often used to describe both "Pogoing" and "Packing".
LOW SIDINGA term that describes what happens when a motorcycle falls to the inside of a turn.
LOW-SPEED DAMINGDamping to control slow vertical suspension movements such as those caused by ripples in pavement.
LSCLow Speed Compression damping circuit is affected most when riding through turns.
LSRLow Speed Rebound damping circuit is affected in the same riding circumstances as LSC.
MID TURN WOBBLEWhen the bike wobbles or weaves near the apex of a turn.
NITROGENAn inert gas used to pressurize the bladder or reservoir of shocks. Some also fill tires with this due to its stability at varying heats.
PACKINGWhen the rear shock is compressed by the wheel hitting one bump and cannot rebound quickly enough to absorb the impact of the second or third bump.
PISTONA cylindrical shaped piece of steel with several ports arranged around the periphery so as to direct oil towards the face of shocks.
PISTON RING A ring that fits around the piston and prevents oil from by-passing the piston and shims.
PISTON RODA small diameter steel rod that fits into the upper legs of cartridge forks. It fastens to the fork cap on one end and holds the rebound piston and shims on the other end.
PITCHA motion fore or aft, when the front end dives or when the rear end squats.
PIVOTA fixed point at which a lever rotates. Example: swinging arm or suspension linkage.
POGOINGWhen the rear shock rebounds so quickly that the rear wheel leaves the ground.
PRE-LOADPre-load is applied to the fork and shock springs in order to bring the bike to the proper ride height or race sag dimension. The pre-load can be biased to change the bike’s steering geometry. High pre-load/less sag in the front forks, will make the steering heavy/slow and more stable at high speed.
PRE-LOAD SPACERMaterial used to adjust a fork's preload internally. Typically, thin-walled aluminum or PVC tubing is used
RACE SAGThis term refers to number of millimeters that the forks or shock sag with the rider on the bike in full riding gear. This is essential to proper suspension tuning but is often overlooked or adjusted incorrectly.
RAKEThe angle between the steering axis and a vertical line.
REAR END SQUATTINGSquatting occurs when you accelerate the motorcycle. The chain forces push down on the rear wheel. The resultant forces are transferred up the swinging arm into the main frame causing a lifting force which extends the front end causing a weight shift backwards.
REBOUND DAMPINGThe damping circuit that affects the stored energy release of the compressed spring in order to reduce the rebounding speed of the damper.
RESERVOIRA cylindrical shaped device that contains oil and nitrogen gas.
RE-VALVINGA term used to describe a fine-tuning service for altering the compression and rebound shims in order to affect a certain damping characteristic that keeps the motorcycle’s wheels following the terrain in many riding situations
RIDE HEIGHTSuspension adjustments (raising or lowering the fork or lengthening or shortening the shock) to alter the chassis attitude of the motorcycle.
ROLLA motion where the motorcycle leans left or right from straight-up riding.
S.A. ANGLEThe angle of rotational motion about the swinging arm pivot axis.
S.A. PIVOT AXISThe point where the swinging arm mounts to the frame and rotates.
SAGThe amount the front or rear of the bike compresses between fully topped out and fully loaded with a rider (and all of his riding gear) on board in the riding position
SEALA rubber or plastic cylindrical shaped piece that prevents oil from being lost from the damper.
SHAFTThe chrome rod on the rear shock that has a clevis on one end and the piston and shims fastened to the other end.
SHIMSA thin, steel, round, flat washer used to exert resistance on the oil flow through a piston. A series of shims (valve stack or valving) with varying outer diameters and thicknesses are arranged in sequence to provide a damping affect.
SHOCK BODYThe aluminum cylinder which contains the damper assembly.
SHOCK DYNOA machine that cycles a shock absorber at different damper speeds and measures the resistance posed by the four damping circuits.
SHOCK FADEA condition that occurs when the shock oilbecomes so hot that it loses it’s transmitability. The damping affect is reduced and the shock compresses easily and rebounds quickly.
SPEED WOBBLEWhen a motorcycle wavers back and forth rapidly at high speeds.
SPIKINGA word used to describe how the forks work when the damping is too stiff/slow. This is also associated with "Arm Pump". The feeling in your arms when your forks aren’t absorbing the energy of impacts to the wheel but instead transfer them to your arms.
SPRINGA steel wire that is wound into a coil shape and tempered in order to provide resistance to compression forces and store energy for release to the extended position.
SPRING RATEA motorcycle suspension springs stiffness, expressed in kg/mm, N/mm or lb/in.
SQUATCompression of the rear suspension as a reaction of weight transfer and/or chain pull. Squat occurs especially usually under rapid acceleration.
STEERING ANGLEThe angle of the handle bars as you rotate them left or right about the steering axis.
STEERING AXISThe axis where the forks rotate in the frame.
STICTIONA combination of the words static and friction. This word is used to describe the tension exerted on the moving damper parts by the stationary parts like the bushings, seals, and wipers. Low stiction is desirable because it has less of an affect on the damping.
STIFF/SLOW SOFT/FASTThese words are used to describe the damping quality of the forks or shock. With regard to the "Clickers", these words refer to the direction of rotation that you will turn the clickers in order to improve the damping. Turning the clickers clockwise will make the damping stiff/slow. Turning the clickers counter-clockwise will make the damping soft/fast.
SUSPENSION FLUIDUsed inside a shock absorber to create damping when forced through orifices or valving. The fluid is also used for lubrication and should be incompressible.
SWAPPINGWhen the rear end of the bike pivots around from side to side very quickly.
SWINGARMThe rear fork that connects the rear wheel to the frame.
TANK SLAPPERWhen the forks rotate from stop to stop rapidly and your arms and body slap back and forth against the motorcycle’s gas tank.
TOPPING OUTOccurs when the suspension extends to its limit. A shock with a spring of the proper rate mounted should have just enough force to top out without a rider on board.
TRAILOn the front end, the horizontal distance between the steering axis at the road surface, to the tire contact point. Generally forks with off-set axles have more trail than forks with straight through axles.
TRANSITION SHIMSThese are shims with very small outer diameters that are used to separate the normal shims of the low and high speed valve stacks.
TRANSMITABILITYThis term refers to the suspension oil’s ability to transmit shock loads. As the oil’s temperature rises, the transmitability falls. Example: With every increase in temperature of 18 degrees Fahrenheit the transmitability of the oil falls 50%.
TRAPPED AIR SPACE The height of the air space that forms in the top of the fork tube between the fork cap and the oil.
TRIPLE-CLAMP ASSEMBLYIncludes the steering stem bottom clamp, and top clamp. The triple clamp assembly connects the forks to the frame.
TRIPLE-CLAMP OFFSETThe distance from the center of the fork tubes to the steering stem center. The greater the offset, the smaller the trail dimension.
UNLADEN SAGThe number of millimeters that the bike sags under it’s own weight without a rider.
UNSPRUNG/SPRUNG WEIGHTThe unsprung weight of the motorcycle are parts like the wheels, brakes, swingarm and suspension linkage, and the lower front fork legs. The sprung weight is all the parts of the motorcycle that are supported by the suspension.
VALVESA term that refers to a series of shims either for the compression or the rebound damping.
VISCOSITYA rating system for oils that measures the oil’s flow rate through a fixed orifice at a certain temperature. Also known as the oil’s weight. Example: SAE 30 Wt.
VISCOSITY INDEXThe flow rate characteristic of the oil over a range of temperatures. The VI rating of an oil is directly linked to the oil’s transmitability. Cartridge fork oil has a VI# of 115. Shock oil normally has a much higher average operating temperature so its VI# is 300.
WASHOUTA term used to describe what happens when the bike and rider fall to the inside of a turn.
WEAVEInstability of the rear of the motorcycle, a side ways movement of the rear end from one side to the other. 
WEIGHT BIASAlso called weight distribution. The amount of weight on each wheel of the motorcycle.
WHEELBASEThe distance between the front and rear axle centers.
WHEELIEA word used to describe a motorcycle in motion with the front wheel off the ground.
WOBBLEInstability of the front end of the motorcycle, a very fast oscillation from side to side of the front end. 
YAWA motion that veers left or right from the motorcycle’s heading angle.

References:  This table is a combination of various internet resources I have found covering the issue, including three primary sources.  The URLs for these sites are here – (1) http://www.twowheelforum.com/37-technical-help-maintenance-tuning/11584-suspension-definitions-other-terminology.html#/topics/11584 (2) http://www.sportrider.com/suspension-tuning-guide-learning-lingo#page-8 (3) http://www.lustracing.co.uk/suspension/motorcycle-set-up-glossary.html

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