MOTO - GLOSSARY: A translation guide for newcomers-and maybe even some old hands, too


For the uninitiated, a maiden voyage into the kingdom of two wheels can be like a trip through some mysterious, alien land. It’s a place where everyone communicates in a language that sounds familiar at first, but you soon realize that all the important words seem to be encrypted in some secret code-and you left your decoder ring on the bus. You feel completely out of your element, like a computer-illiterate trying to make small-talk at a Geek Squad convention.

One of the first things you encounter is an alphabet soup capitalized initials—EFI. ABS, TDC, CV. Okay, Vanna, can I buy a vowel? Equally confusing is the recurring use of terms such as “done.” Geez. what’s that, a misspelling of “doohickey?” Even many of the words you do recognize seem totally out of place. Rake and trail? Sounds like something you’d read in Better Homes & Gardens. Floating discs? Sorry, the UFO convention was last week. A rear end that needs more rebound? Hey, is this a review of a motorcycle or a profile of John Goodman? No wonder newcomers feel like they’re trapped in the Land of the Lost.

But don’t panic: Help is on the way. As motorcycle journalists, we are not only quite familiar with the terminology of two wheels, we probably helped create some of it. Sorry; it’s a hazard of the trade. But to help you get up to speed as you begin your Ride of Passage into motorcycling, we’ve assembled a collection of the terms you’re most likely to bump into along the way, and given them clear, concise definitions in lay language.

It is not our intention, though, to define the entire lexicon of motorcycling; so, you won’t find every conceivable technical term or example of industry jargon here. To contain that volume of information, this magazine would have to be thicker than the phone book your Aunt Sophie sits on when she drives the Buick. But by the time you get to the end of the list, you’ll know that “piggyback reservoir” has nothing to do with the water supply, and that “tail trunk” is not a body part on a deformed elephant.

Enjoy the read. And especially the ride.

ABS Abbreviation for Anti-lock Braking System, a technology that prevents the wheels from skidding when the brakes are applied, regardless of the condition of the road surface.

Afterfire Often mistakenly referred to as a “backfire,” this is the loud “pop” that emanates from the exhaust system of some bikes, usually when the throttle is closed and the engine is returning from higher rpm to idle. Afterfire is most common on engines with performance and exhaust modifications, and it is caused by a small accumulation of unburned fuel in the exhaust that is ignited by the departing hot gases.

Aftermarket The segment of the motorcycle industry that is devoted to the manufacture, distribution and sale of parts and accessories. The term stems from the fact that this is the part of the motorcycle “market” that comes into play “after” the sale of the motorcycle.

Airbox An enclosure that houses the air-cleaner element and is connected to the intake mouth of the carburetors or the fuel-injection throttle bodies. It consists primarily of the fresh-air intake opening, the air-filter clement and any tubes needed to route air into the individual intakes.

Alloy A metallurgical description of a material that results from the mixture of two or more metals (not always aluminum), or of a metal and some other element.

Apex The point at which a bike (or car) reaches the inside-most part of the turn when following the optimum line through a corner.

Aspect ratio The relationship between a tire’s width (measured across the widest part of its tread) in proportion to its carcass height (measured from the inside diameter of the bead to the point where the tread touches the ground). In the sizing designation of most modern tires, the first dimension is the width, and the second dimension is the aspect ratio. A 180/55 tire, for example, is 180mm wide and has a 55-pereenl aspect ratio, which means its carcass height is 99mm (55 percent of 180).

Backbone frame A type of frame in which the main structural member is a large, usually single round, square or rectangular tube-not unlike a back-bone-that runs from the steering head, under the gas tank, to a junction somewhere between the front of the seat and the lower frame rails.

Backfire The popping sound made when the combustion in a cylinder or cylinders occurs before the affected intake valves can completely close. This allows part of the combustion to travel past the valve, up through the intake tract and out through the airbox.

BDC Abbreviation for Bottom Dead Center, the precise point of crankshaft rotation at which the piston has descended to its absolute lowest point in the cylinder.

Bern A relatively firm buildup of dirt, either deliberate or accidental, on the outside of a corner in various forms of off-road racing. Berms are particularly beneficial in motocross, where riders regularly use them to make faster and more abrupt directional changes.

 

Bias-ply tire A tire in which the carcass (the main body of the tire) is constructed of layers of fabric that has its woven grain placed at angles relative to one another.

Billet A large bar or block of metal (often but not necessarily aluminum) from which a component is machined.

Black box A slang term used to describe a sealed, solid-state electronic module that controls the ignition, the fuel-injection system or both. Often called the ECU (Engine Control Unit) or ECM (Engine Control Module).

Bobber A type of modified bike that gained popularity after WWII when riders began stripping bikes down to the bare minimum, often for competi­tion purposes, giving them a “bobbed” appearance.

Cafe-racer A motorcycle cither modified or built for twisty-road performance. The term was coined in England during the Sixties to describe bikes ridden by groups of riders who would race from cafe to cafe.

Cartridge fork A type of telescopic front fork in which damping is con­trolled by oil forced through a stra­tegically placed valve body, called a cartridge, inside each fork tube.

Chopper A style of stripped-down custom bike, popularized by the movie Easy Rider, that involves radically raked-out forks, tiny gas tanks, high handlebars and, frequently, hardtail rear ends.

Chrome-moly Shortened name for a very strong steel that contains chro­mium, molybdenum, carbon and iron. The most popular type of chrome-moly steel is called 4130, the categorization given it by the American Iron and Steel Institute (AISI).

Clip-ons Separate right- and left-side, roadracing-style low handlebars, each of which attaches to the fork by clamping around its respective fork tube rather than bolting to the top triple-clamp.

Contact patch (footprint) The total area and shape of the point where a tire touches the ground.

Continuously Variable Transmission (CVT) A type of automatic transmis­sion in which the effective gear ratios change infinitely and without notice­able steps between maximum and minimum designed-in ratios.

Counterbalancer A crankshaft-driven weight or set of weights in an engine which create an imbalance equal to, but in the opposite direction of, the imbal­ances inherent in many engine configu­rations. The vibrations caused by these opposing imbalances largely cancel one another, resulting in a very smooth-running engine.

Countersteering The means by which a motorcycle turns at any speed much above a walking pace. To turn the motorcycle left, the rider must push the handlebar to the right, and vice versa.

Cruiser A broad category of motorcy­cles that more or less exude traditional American-bike styling, with a riding position and a performance profile that make them more conducive to casual cruising than to aggressive, sporty riding.

CV carburetor A type of carburetor that uses a twistgrip-controlled but­terfly valve and a vacuum-regulated neoprene diaphragm atop the slide. The twistgrip moves the butterfly, but the actual slide opening is dictated by the differential in vacuum above and below the diaphragm. This tends to keep the speed of the intake air through the carburetor fairly constant, giving the carb its “constant velocity” (CV) designation.

Damping The slowing down of a spring’s natural tendency to compress and extend very quickly. On a motor­cycle, damping is provided by either a shock absorber or the damper unit in a fork assembly. Damping that prevents the suspension from compressing too quickly when it hits a bump is called compression damping; damping that prevents it from returning to its normal position too quickly is called rebound damping.

Desmodromic A type of valve-actua­tion system exclusive to Ducati that eliminates valve float by using two cam lobes per valve and no valve springs; one lobe mechanically pushes the valve open and the other lobe mechanically pushes it closed.

Double overhead cams (dohc) A cylinder-head arrangement that locates two camshafts-one intake and one ex­haust-in the uppermost portion of the head, above the combustion chamber.

Dry sump A type of engine-oiling system so named because the bottom of the engine’s crankcase (the “sump”) is not used as a reservoir for the oil; the oil instead is pumped back and forth from a remote container called an oil tank.

Dual-purpose (or dual-sport) bike A type of motorcycle designed to perform capably as both a road bike and an off-road bike.

ECU (Electronic Control Unit) or ECM (Electronic Control Mod­ule) The computerized “black box” that controls the fuel metering of a fucl-injcctcd engine as well as spark timing. On certain other models, it also controls other functions, including throttle-body butterfly opening, exhaust powervalve operation and even brake-force proportioning.

EFI Abbreviation for Electronic Fuel Injection

Enduro (1) A form of off-road compe­tition in which riders must cover a pre­determined course while maintaining an exact average speed, with penalties incurred for being either late or early; (2) a type of motorcycle specifically designed for this form of competition.

Ergonomics The science of designing a proper relationship between people and their workplace. In motorcycling, the term is commonly used to refer to a bike’s overall scaling position and control layout.

Exhaust powervalve (two-stroke) A movable valve in a two-stroke engine’s exhaust port. The valve adjusts accord­ing to rpm, thereby helping the engine produce a broader range of power by varying the exhaust-port timing. In most cases, the valve is adjusted by mechanical means, but a few bikes do it electronically.

Exhaust powervalve (four-stroke) An electronically controlled valve in a four-stroke engine’s exhaust system that opens and closes according to rpm, thereby changing the resonant tuning of the system to improve performance in a given rpm range.

Expansion chamber A type of exhaust system used on a two-stroke engine. It routes exhaust gases into a header pipe that opens up into a large-volume chamber (hence, the “expan­sion chamber” name), then funnels back down into a small-diameter pipe. The length, location and diameter of an expansion chamber’s various sections have a critical effect on engine perfor­mance by affecting the action of the exhaust pulses.

Fairing The wind-deflecting bodywork on the front of a motorcycle.

Final drive The means by which engine power is delivered from the transmission to the rear wheel. The most popular types are chain drive, belt drive and shaft drive.

Fly-by-wire A term, borrowed from the aviation industry, to describe throttle butterflies that are opened elec­tronically rather than by a conventional throttle cable. A few motorcycles even have braking systems whose stopping is regulated electronically.

Fork gaiters The accordion-type rub­ber boots that cover the exposed tubes of some motorcycle forks.

Four-stroke A type of engine that re­quires two full revolutions of the crank­shaft (hence, four separate up/down strokes of the piston) to accomplish one complete power-producing cycle.

Fuel-injection A system that sprays fuel into the intake system via elec­tronically operated nozzles whose duration of opening is controlled by the ECU. The amount of fuel sprayed at any given moment is determined by the ECU’s interpretation of the data sent to it by numerous sensors (rpm, throttle position, engine temperature, air density and others) that are located on or around the engine.

Hanging off A roadracer’s method of changing a bike’s effective center of gravity for faster cornering by sliding as far off the seat as possible toward the inside of the turn. He usually hangs off far enough to drag his inside knee.

Hardtail A type of motorcycle chassis that has no rear suspension whatsoever.

Hydraulic lash adjusters Small de­vices, much like hydraulic valve lifters, mated to the cam followers of some engines and that use engine oil pressure to automatically maintain zero valve clearance, thereby eliminating the need for periodic valve adjustments.

Injection mapping The programming in an ECU that determines the desired fuel mixture under all operating condi­tions based on input from the various sensors on the engine. Some OEM injection systems can be adjusted, but most have a limited range of adjustment to prevent the mixture from exceeding the legal emissions parameters. For per­formance-modified engines, numerous aftermarket devices are available that allow a greater range of adjustment.

Knee sliders The hard plastic pucks that attach via velcro to the knees of roadracing leathers. The pucks allow the rider’s knees to glide easily over the track surface when he hangs off and drags them in the corners.

Megaphone Either a muffler or an unmuflled exhaust outlet shaped like a funnel or a megaphone. The mega­phone’s length, degree of divergence and diameter of its final opening can have great effect on engine tuning.

O-ring chain A type of final-drive chain in which the individual rollers are scaled (to keep dirt out and lubricant in) by little rubber O-shaped rings between the sideplates.

Monoblock brake caliper A caliper machined from a solid block of metal, as opposed to two-piece calipers that boll together. The monoblock style is stronger by virtue of being a single piece. Brembo’s version of the monob­lock caliper is spelled “Monobloc.”

Overhead valve (ohv) A cylinder-head design in which the valves enter the combustion chambers from above, but the camshaft is located below the cylinders and the valves are actuated via pushrods and rocker arms.

Oversquare A term used in reference to an engine that has a bore dimension larger than its stroke dimension.

Perimeter frame A frame design built around two large, main members that make the crucial steering-head-to-swingarm pivot connection in a straighter line by bending slightly around the outside of the cylinder head(s) rather than looping around the entire engine from above.

 

Piggyback reservoir A type of shock absorber on which a separate fluid res­ervoir is attached directly to the body of the shock itself—thus earning the name *’piggyback”-rather than mounted re­motely at the end of a hydraulic hose.

Pillion The term sometimes used to describe the passenger’s seat on a motorcycle.

Powdercoat A method of painting that applies paint electrostatically in a dry powder form instead of via a spray gun as a liquid. The object to be painted is electrically grounded, and the powder is sprayed with a positive charge, which causes the powder to stick to the object. The object is then heated in an oven at a temperature sufficient to make the powder melt, causing it to bond firmly to the object.

Powcrband The rpm range in which an engine makes its strongest and most consistent power.

Power-to-weight ratio The relation­ship between the amount of horsepower any given engine produces and the amount of weight that power must propel. A motorcycle that weighs 500 pounds and has a 100-horscpowcr engine, for example, has a 5-lo-l (or, more accurately, a 1 -lo-5) power-to-weight ratio.

Preload The compressive force applied to a spring that is captured within a sus­pension component before that spring is compressed any farther by normal use. The preload on most shocks and many forks can be adjusted to compen­sate for load and riding conditions.

Primary drive The means by which power is delivered from the crankshaft to the transmission. Primary drive can be via gears, a chain, a belt or a gear-chain combination.

Radial tire A type of lire in which the carcass (the main body of the tire) is constructed of layers of fabric that has its woven grain placed at a 90-degrcc angle relative to the tire’s direction of travel. In other words, the grain runs from one side of the tire to the other in the shortest possible distance, which is directly from one bead to the other.

Radial-mount brakes A front-brake mounting that attaches the caliper with mounts at both ends rather than at the trailing edge, and with bolts oriented parallel to the rotor instead of perpen­dicular to it. This system reduces cali­per flex and also makes for easy changes in rotor diameter while retaining the same caliper.

Radial-mount master cylinder A design that positions the master-cylinder piston perpendicular to the handlebar rather than parallel to it. This reduces flex at the master-cylinder mounting point, providing more-positive braking feel.

Rake A more informal term for steer­ing-head angle.

Rearsets Foot controls mounted rather high and rearward to allow sufficient cornering clearance and provide ideal lower-body positioning for roadracing and serious sport riding.

Redline The maximum safe rpm of an engine, generally indicated by red markings on the tachometer at engine speeds above that limit.

Remote reservoir A type of shock absorber on which a separate fluid reservoir is attached to the main body by a hose, allowing the reservoir to be mounted somewhere other than on the shock body itself.

Repli-racer (or racer-replica) A type of motorcycle specifically designed to look (and usually function) like a roadracing bike.

Rev limiter A device that restricts an engine’s maximum speed by cutting the electrical supply to the ignition coils at a predetermined rpm. On some fuel-injected motorcycles, the rcv-limitcr system also cuts off the supply of fuel to the cylinders.

Roll-on The acceleration produced by simply rolling the throttle wide-open in any given gear without downshifting.

Secondary butterflies A second set of butterfly valves placed in the throttle bodies of a fuel-injection system. The primary butterflies open in exact pro­portion to the movement of the twist-grip by the rider, but the opening of the secondaries is controlled electronically by the ECU Since the secondaries are upstream of the primaries, they effectively control the actual throttle opening, not the primaries. This design is intended to provide smoother, more controllable rates of acceleration under some conditions as well as allow the engine to meet all applicable emissions standards.

Shift drum The barrel-shaped device in the transmission cluster that moves the shift forks side-to-side to engage the appropriate gears as the rider oper­ates the shift lever.

Single in-head cam (sihe) A type of cylinder head used by BMW and Moto Guzzi in which the camshaft is located in the lower part of the head, below the combustion chamber, and operates the valves via very short pushrods and traditional rocker arms.

Single overhead cam (sohc) A cyl­inder-head arrangement that locates a single camshaft in the upper portion of the head above the combustion cham­ber and that usually operates the valves through rocker-type cam followers.

Slipper clutch A type of clutch that is designed to slip slightly when the transmission is downshifted and engine rpm is significantly below the correct road speed for the selected gear. This slippage helps prevent rear-wheel hop and chatter during hard braking.

Spark arrestor A device that fits on the end of an off-road or dual-purpose bike’s exhaust system and eliminates the likelihood of exhaust-ignited forest fires by preventing hot, glowing pieces of carbon from being expelled from the exhaust.

Steering damper A small hydraulic cylinder that looks and operates much like a miniature, springless shock absorber and that mounts between the front fork and the frame. The damper reduces the tendency of some forks to oscillate back-and-forth at higher speeds. Some bikes also have electronic steering dampers that arc controlled by the ECU and regulate damping force according to the motorcycle’s speed.

Steering geometry A term used to describe the geometric relationship of several critical dimensions (steer­ing-head angle, front wheel trail, triple-clamp offset and angle, etc.) that determine a motorcycle’s overall steer­ing characteristics.

Steering-head angle The exact angle of the steering head, which is the large, short piece of tubing located at the very front of a motorcycle frame, and in which the entire fork assembly pivots to steer the motorcycle. Steering-head angle is usually measured in degrees from vertical.

 

Stiction A combination of the words “stick” and “friction.” It describes the tendency of friction to cause certain components to stick slightly as they try to slide against one another, such as a front-fork tube sliding within its fork leg.

Stoppie (or nose wheelie) Riding a motorcycle only on its front wheel. This occurs when the rider applies enough front-brake force, usually deliberately, to a moving motorcycle to make the rear wheel lift off the ground. When this is done as a stunt, the rider con­stantly modulates front-brake pressure to keep the rear wheel in the air as long as possible.

Stroke The exact distance a piston travels as it moves from Top Dead Cen­ter to Bottom Dead Center.

Swingarm The long chassis member that connects the rear wheel to the frame, and that pivots at its forward end lo allow rear suspension movement.

TDC Ab­breviation ofTop Dead Center, which is the precise point of crankshaft rotation at which the piston has ascended to its highest position in the cylinder.

Terminal speed The maximum speed reached during a standing-start quarter-mile acceleration run.

Thumper Expression commonly used to describe a large-displacement, four-stroke, single-cylinder engine.

Tail trunk (or tour trunk or top trunk) The large storage trunk mounted behind the passenger seat on many touring-oriented motorcycles.

Traction control A system by which a motorcycle’s ECU detects excessive slippage of the rear wheel and curtails that slippage by either retarding the ig­nition system’s spark, the fuel-injection system’s delivery of fuel, or both.

Trail Often called front-wheel trail, this is the dimension of a motorcycle’s steering geometry that gives the front wheel its self-centering effect. Trail is measured by drawing an imaginary line through the center of the steering head until it intersects with the ground, then drawing another imaginary line in a vertical plane from the center of the front axle to the ground. The distance between the points where those two imaginary lines intersect the ground is the trail.

Trail-braking The practice of apply­ing the front brake as a bike is being leaned into a corner. The farther the bike enters the corner and the greater the lean angle, the less braking force should be applied to reduce the pos­sibility of the front tire losing traction and causing a fall.

Trellis frame A type of frame design composed of a number of short, some­times curved tubes welded together in a way that forms a very rigid, triangu­lated structure that looks somewhat like a trellis.

Triple-clamps (or triple-trees) The two strong, usually similar supports on a telescopic fork that clamp to three key parts of the fork (both fork tubes and the steering stem) just above and below the steering head.

Two-stroke A type of engine that re­quires only one revolution of the crank­shaft (and hence, just two up/down strokes of the piston) to complete one set of power-producing events. Such an engine is often called a “two-cycle,” but that appellation is incorrect; both two-stroke and four-stroke engines require four separate cycles (intake, combus­tion, power, exhaust) to make power, and reciprocating engines are classi­fied according to the number of piston strokes required to complete all four of those cycles.

Undersquare A term used in reference to an engine that has a bore dimension smaller than its stroke dimension.

Unsprung weight Any part of a vehicle’s weight that is not supported by the suspension’s springs. The wheels and tires are unsprung weight, as are the brakes and the parts of the suspen­sion that move up-and-down with the wheels.

Upside-down fork A type of tele­scopic front suspension in which the fork tubes are mounted where the slider legs would normally be located (attached to and moving up-and-down with the front wheel) on a conventional fork, and with the slider legs positioned where the tubes traditionally are found (held firmly inside the triple-clamps). This role reversal led to this fork design being labeled “upside-down.” They also are sometimes also called “male-slider” or “inverted” forks.

Valanced fender A fender with very tall sides that wrap around the tire far enough that no daylight is visible between the top of the tire and the sides of the fender.

Wet sump (1) A type of engine-oil­ing system in which the bottom of the engine’s crankcase (the “sump”) serves as the reservoir for the oil supply; (2) a description of the action that takes place when a dry-sump system mal­functions and allows oil to accumulate in the crankcase.

Wheelbase The exact distance be­tween the centers of a motorcycle’s two wheel axles, measured with the front wheel aimed directly forward.

X-ring chain A type of chain very similar to the O-ring type except that its rubber sealing rings are X-shaped in cross-section rather than circular. This design allows the rings to flex more easily for reduced wear, and it also provides two sealing edges and captured lubrication pools instead of just one. A variation is the XW-ring, which is W-shaped in cross-section to provide three scaling edges.