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Acronyms, Terms & Definitions

ABS	Anti-lock Braking System
APRC	Aprilia Performance Ride Control
ASC	Automatic Stability Control
Auto Blipper
Bore and Stroke	Relationship between the diameter of a cylinder and the length the piston travels
Brake Calipers	Fixed and Floating Calipers
Camshaft	Single or Double Overhead Camshaft (SOHC or DOHC), Pushrod
Carburetor	Blends air and fuel for an internal combustion engine.
Catalytic Converter	Converts harmful emissions to harmless compounds
Cellasto	Microcellular polyurethane elastomers that enhance driving comfort
Clutch	Multi-plate, wet, dry
Compression Ratio	Ratio of the volume of a combustion chamber from its largest capacity to its smallest capacity
Counter Steering	"Steer left to turn right"
Crankshaft	Transforms the energy from the pistons (lineary) into a rotary motion
CVT	Continuous Variable Transmission
CDI	Capacitor discharge ignition

Desmodromic Valve	A reciprocating engine valve that is positively closed by a cam and leverage system
Disc Brakes	Difference between fixed and floating disc brakes
DOHC	Double Overhead Camshaft
Drum brakes	Single or twin leading shoe
DSS	Ducati Skyhook System
ECU	Electronic Control Unit
EFI	Electronic Fuel Injection
ESA	Electronic Suspension Adjustment
EXUP	Exhaust Ultimate Power Valve
Floating Sprocket	To help keep the sprocket properly aligned
Four Stroke Engine	Most popular modern motorcycle engines
Gear Ratios	Explaining the relationship between various components and how it impacts on power delivery
GVWR	Gross Vehicle Weight Ratio
High Side	Losing control as a result of extraordinary power added to the rear wheel
Hub-center steering	An alternative front-end steering/suspension system
Knucklehead Engine	Harley-Davidson motorcycle engine
Leading shoe	Drum brake - single or twin leading shoe

Monolever
Multi-plate clutch	The most common motorcycle clutch
Paralever	Eliminating "jacking" in a shaft driven bike
PCM	Powertrain Control Module
Power and Torque	Both are needed to get your bike moving. But what is it?
Pre-unit just & Unit construction is	Pre-unit just means that the engine crankcase and gearbox are two separate units bolted into the same frame, whereas unit construction means the gearbox and crankcase share the same casing. Early motorcycles were largely pre-unit as it was simpler to cast gearbox and engine casings separately at the foundry, and manufacturers could buy in engines and/or gearboxes and pair them up without any major issues. Unit construction is used for essentially all modern motorcycles, it results in a lower total weight, much better rigidity, fewer places to leak oil, and improved simplicity.
Pushrod	Camshaft located inside the engine rather than in the head and driven by pushrods
Quick shifter
Radial Brakes	Radial or Axial Brake Calipers
Rake	The angle between the neck a bike and a vertical line
Ram Air	Increasing engine power through the use of airflow
Reed Valve	A valve opening under vacuum to allow fuel/air mixture to enter the crank of a 2-stroke
RFVC	The RFVC indication on the head off the engine means: Radial Four Valve Combustion. RVFC or Radial Four Valve Combustion was a proprietary valve arrangement created by Honda to make a four valve head flow more like a hemi head. The splayed valves arrangement allows quicker flame propagation across the combustion chamber, allowing the engine to produce more power at a given RPM.
Ride by Wire	The use of electrical or electro-mechanical systems for performing vehicle functions traditionally achieved by mechanical linkages/acruatiors
Seamless Gearbox	Also referred to as seamless shifting, seamless transmission or Zeroshift transmission
Shock Absorbers	Single tube, double tube, front, rear

Slipper clutch
SOHC	Single Overhead Camshaft
Steering Damper	Inhibits undesirable movement of the steering mechanism.
Supercharging	How these forced air induction systems work and why they are the way of the future.
Sump	Wet and dry sump
Suspension adjustment	Also covering both front and rear suspension rebound and compression settings
Swingarm	The main component of the rear suspension to hold the rear axle firmly, pivot vertically, allowing the suspension to do its work.
Tank Slapper	An unwanted, quick and scary oscillation of the front wheel
Telelever	A BMW patented front suspension system
Torque	Refers to force - read power and torque
Traction Control	Designed to prevent loss of traction of road driven wheels
Trail	The distance between tyre surface contact and a vertical line from the axis to the surface
Triple Tree	Central to the steering mechanism of a bike
Turbocharger	Boosting an engine without significantly increasing weight
Two Stroke Engine	Mainly used on smaller bikes, such as 50 cc. Reducing in popularity due to pollution
VTEC	Variable Valve Timing and Lift Electronic Control
Weight Dry vs Wet/Curb	Dry weight is what the bike weighs without fluids - without gas, oil, coolant, final drive fluid, or sometimes even the brake fluid and battery. Motorcycles are typically shipped dry for ease of handling and safety. Wet weight/curb weight is a term used to refer to the weight of a motorcycle when it has been loaded with all the fluids it needs to operate, along with the battery. Generally only a half tank of gas, ready to ride. But these terms are not standardized across the industry.
Wheels	A discussion on spoke and alloy wheels
YPVS	Yamaha Power Valve System

Tech Videos

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