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CAR TERMINOLOGY GLOSSARY

Car Match

GLOSSARY

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A

Active Suspension – An often complex, computer-controlled suspension system that uses powered actuators instead of conventional springs and shock absorbers. The actuators position a car's wheels in the best possible manner to deal with road disturbances and handling loads.

Adjustable Suspension - A suspension system that allows the driver to adjust the handling / ride balance through a variety of means, most often through adjustable or magnetorheleological shock absorbers.

Air Dam- A front spoiler mounted beneath the bumper and shaped to reduce the airflow under the car. Air dams can increase the airflow to radiators, reduce aerodynamic drag, and/or reduce lift.

Air Spring / Suspension- An air bag, often made of a strong rubber, making up part of a car's suspension that supports the weight of a car at each corner in lieu of a standard coil spring.  Air springs, most commonly fitted to luxury cars, provide excellent ride quality but are often trouble prone due to leaks, which often develop as the air springs and related components become old and brittle.

All-wheel-drive – Commonly used interchangeably with four-wheel-drive / 4wd, all-wheel-drive is a drivetrain configuration by which all four of a car's wheels are driven with power from the engine all the time.  In contrast, four-wheel-drive / 4wd more commonly refers to a drivetrain configuration in which all four wheels of a car are only driven part-time (generally, when the driver so selects via a lever or switch).

Anti-Lock Braking System(ABS) - A braking system that prevents the wheels from locking up during hard braking.  ABS can shorten braking distances and provides the driver with more control during hard braking, in particularly, maintaining the car's ability to steer. ABS has become standard on most new models.

Anti-Roll / Stabilizer Bar- A suspension element (used at the front, the rear, or both ends of a car) that reduces body roll by resisting any unequal vertical motion between the pair of wheels to which it is connected. An anti-roll bar does not affect suspension stiffness when both wheels are deflected equally in the same direction. Some high-end luxury / sports cars employ technology to decouple anti-roll bars during straight driving, improving the car's ride quality.  Often incorrectly called a sway bar.

Around-view Camera - A camera system that puts images from around the entire car onto the infotainment / navigation screen.  The view usually consists of four views - behind, either side and in front.

Aspect Ratio- Used in tire terminology, it is the ratio of the unloaded sidewall height of a tire divided by its overall width. A lower aspect ratio tire, often referred to as a low profile tire, implies a shorter, wider tire.  Generally, ride quality decreases with a decrease in aspect ratio, but steering response improves.

Automatic or Automatic Transmission- A transmission that automatically shifts between gears without driver intervention.  Automatic transmissions are further distinguished from automated manual transmissions, DCT or CVT transmissions by the fact that they employ planetary gearsets, given them smoother shift quality than automated manual transmissions, DCT or CVT transmissions.  Certain automatics feature paddle shifters or other varieties of gear selectors allowing drivers to manually shift up and down through the gears.

Automatic Climate Control - A climate control that works like the climate control in your house - you simply set the temperature and the system adjusts the car's air conditioning / heater to the appropriate level to reach and maintain that temperature.

Axle Articulation- See Suspension Articulation.

Axle Tramp- A form of wheel hop that occurs on cars with live axles, caused by the axle repeatedly rotating slightly with the wheels and then springing back.

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B

B-pillar- The structural pillar between a car's front door and rear side, if there is one.

Balance Shaft- An internal shaft in an engine shaft that cancels some of the vibration produced by an engine, making the engine smoother. Only used (and not essential) in engine configurations that are not inherently balanced. Balance-shafted four-cylinder engines use two shafts turning in opposite directions on either side of the engine's crankshaft, while three-cylinder and V-6 engines us a single balance shaft.

Ball Joint- A flexible joint consisting of a ball in a socket, used primarily in front suspensions because it can accommodate a wide range of angular motion.

Beam Axle- A rigid axle supporting the non-driven wheels. Also called a dead axle.

Beltline- The line running around a car's body formed by the bottom edges of its glass panels.  Sometimes erroneously used synonymously with "Cowl."  Many modern cars have high beltlines for a variety of reasons, including side-impact safety regulations and contemporary styling preferences.  Higher beltlines hurt outward visibility.

Bevel Gears- A gearset employing gears shaped like slices of a cone, which allows the axes of the gears to be nonparallel. Bevel gears are used to transmit motion through an angle.

Blind Spot Detection - A system that detects whether there is another vehicle in a blind spot (usually off to either side and behind) and alerts the driver, either through an illuminated warning light, loud noise or vibration of the presense of such a car in the blind spot.  Blind Spot Detection can be helpful in today's cars with high sills, especially when changing lanes.

Boost Pressure- The increase above atmospheric pressure produced inside the intake manifold of an engine by a supercharger or turbocharger. It is commonly measured in psi, inches of mercury, or bar and may simply be referred to as "boost."

Brake Assist - A system that increases braking pressure in an emergency situation (because driver's usually fail to do so).

Brake Torqueing- A procedure used in performance tests to improve the off-the-line acceleration of a car equipped with an automatic transmission. It is executed by firmly depressing the brake with the left foot, applying the throttle with the car in gear to increase engine rpm, then releasing the brakes. Brake torqueing is particularly effective with turbocharged cars because it helps overcome turbo lag.  Brake torqueing is almost never done by real drivers because it is hard on a car's components.  Thus, the acceleration numbers reported in most magazines are often inflated numbers that most consumers will never experience.

Breathing (engine)- A term used to describe an engine's ability to fill its cylinders with air-fuel mixture and then discharge the burnt exhaust gases. Generally, better breathing results in more power.

Bushing- A simple suspension bearing that accommodates limited rotary motion, typically made of two coaxial steel tubes bonded to a sleeve of rubber between them. The compliance of the bushing in different directions has a great effect on ride harshness and handling.

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C

C-pillar- The roof pillar between a car's rearmost side window and its rear window. On a vehicle with four side pillars, the rearmost roof support may be called a D-pillar.

Cam Profile- The shape of each lobe on a camshaft. The profile determines the amount, or "duration," of time the valve is open; it also largely determines the valve's maximum opening, or "lift."

Camber- The angle between the plane of a wheel's circumference and a vertical line, measured in degrees and minutes. The tops of a car's wheels tilt inward when the camber is negative, outward when it is positive.  Many cars run negative camber to improve handling, although this can increase wear on the inside of the tire.

Camshaft- A shaft fitted with several cams, whose lobes push on an engine's intake valves to allow are into the engine.  Engines can have one or multiple camshafts.  If an engine has one camshaft, it is usually a "pushrod" or "OHV" engine, which are made exclusively by domestic (American) manufacturers.  Foreign manufacturers make "OHC" or "DOHC" engines, with the camshaft situated above the cylinder head.

Captain's Chairs- Usually used in the context of minivans, SUVs and vans, captain's chairs are two independent bucket seats in the second row of the vehicles, instead of a bench seat that spans the width of the vehicle.  Captain's chairs allow for space between the seats, which allow a pass-through to the third-row and provide separation which can be more comfortable for the occupant's, especially older children.

Carbon Fiber- Short for carbon fiber reinforced polymer or plastic is An extremely strong (for its weight) fiber-reinforced polymer which contains carbon fibers.  Carbon fiber is finding increased use in cars for body panels and even chassis components because it can improve performance as a result of its reduced weight.  However, it remains very expensive.

Caster- The angle between a vertical line and the car's steering axis when viewed from the side, measured in degrees and minutes.

Catalytic Converter- Often simply called a "catalyst", this is a canister fitted to a car's exhaust system that contains a thin layer of catalytic material (some combination of platinum, rhodium, and palladium) that through chemical reactions converts an engine's exhaust emissions into less harmful products.

Center Differential- A differential used in four-wheel-drive systems to distribute power to the front and rear differentials.

Centrifugal-type Supercharger- A supercharger that generates boost pressure through centrifugal force, often through either a belt or gear drive from the engine's crankshaft.  Centrifugal superchargers often do not produce significant boost pressure until high rpm, meaning they do not significantly increase power at low rpm (during normal operation conditions).  This is as opposed to roots-type and screw-type superchargers, which produce significant boost at low rpm and increase torque, improving power during every-day driving.  Centrifugal-type superchargers are a popular aftermarket product and are not used on any current new production cars.

Chassis- A general term that refers to a car's structural frame. In cars with unitized construction, known as a "unibody", the chassis comprises everything but the body of the car.

Coil Spring- A strong metal spring making up part of a car's suspension that supports the weight of a car at each corner.  Coil springs are extremely durable and long-lasting (as opposed to air springs), but often cannot match the ride quality of air springs.

Combustion Chamber- The space within an engine's cylinder when the piston is at the top of its travel, formed by the top of the piston and a cavity in the cylinder head. Since most of the air-fuel mixture's combustion takes place in this space, its design and shape can greatly affect the power, fuel efficiency, and emissions of the engine.

Compliance- A slight resiliency, or "give," designed into suspension bushings to help absorb bumps. Good compliance allows the wheels to move rearward a bit as they hit bumps but doesn't allow them to move laterally during cornering.

Compression Ratio- The ratio to which the air inside an engine's cylinder is compressed. Higher the compression ratios, allow an engine to extract more mechanical from its air-fuel mixture, but also make detonation more likely.  Direct Injection systems allow higher compression ratios without detonation because the fuel system cools the air-fuel charge in the cylinder.

Connecting Rod- The metal rod that connects a piston to a throw on a crankshaft.

Constant-Velocity Joint or CV Joint - A universal joint on the end of a drive axle that allows the axle to transfer power to the wheels while the wheel is turning or the suspension is articulating.  CV Joints often wear out prematurely if the rubber seal or "boot" covering them cracks or tears.

Control Arm- A suspension element that has one joint at one end and two joints at the other end, typically the chassis side. Also known as a wishbone or an A-arm.  Generally control arms are accepted as the best suspension configuration, as they all the tire to maintain optimal contact with the road throughout the suspensions travel.  Control arms are also amongst the most expense suspension configurations, and accordingly limited to luxury and sports cars.

Convertible / Cabriolet- A car that has a folding / removable roof, whether made of fabric, plastic or metal.

Cornering Limit- The maximum speed at which a car can negotiate a given curve.

Coupe- In common vernacular, a closed car with two side doors.  Technically to be a coupe, a two-door car must also have less than 33 cubic feet of rear interior volume according to measurements based on SAE standard J1100.  Coupes are usually differentiated from hatchbacks in that they have a trunk or cargo compartment separate from the passenger compartment.

Cowl - The top portion of the front part of car's body, forward of the two front doors, to which are attached the windshield and dashboard – essentially the area about the dashboard.  Sometimes erroneously used synonymously with "Beltline."  Many modern cars have high cowls for a variety of reasons, including contemporary styling preferences.  Higher cowls hurt outward visibility.

Crash Prevention System - A system that, through a variety of sensors, determines that your car is approaching another vehicle, person or object too quickly and, if the driver fails to react in due time, automatically, applies the brakes in order either to avoid the collision or reduce the impact speed.Often paired with Crash Preparation Systems, and most common on luxury models.

Crash Preparation System - A system that, through a variety of sensors, determines that accident is imminent and prepares the interior restraint systems for activation, thereby saving valuable milliseconds.

Crankshaft- A shaft running through an engine that is coupled by connecting rods to the engine's pistons. Together, the crankshaft and the connecting rods transform the pistons' reciprocating motion into rotary motion, and send the engine's torque to the transmission.

Crossover / CUV – A subset of Sport Utility Vehicles / SUVs that share the wagon-like body and tall stance, but are built on a car-based chassis instead of a truck-based chassis.  Crossovers are not as rugged as traditional SUVs, but handle better and general get better fuel economy. 

CVT or Constantly Variable Transmission- A transmission that employs components giving it a infinite number of gear ratios within a range.  Many CVTs operate in an entirely automatic fashion and do not require driver intervention, although some allow for a degree of manual control via paddle shifters.  Some CVTs are designed to mimick the feel of a traditional automatic to please consumers.  The CVT's primary advantage is that it is often very efficient because it allows the engine to operate in its ideal range, and thus, CVTs can have excellent fuel economy.  CVTs do have disadvantages including that many examples hold the engine to high revs, leading to an annoying drone and historically CVTs have failed at relatively low mileage and been a maintenance headache.

Cylinder- The round, straight-sided cavity in which the pistons move up and down.  The numbers of cylinders, and their arrangement determine an engines configuration (ie, inline four-cylinder, V-6, etc.)

Cylinder Head- The aluminum or iron casting on an engine that houses the combustion chambers, the intake and exhaust ports, and much or all of the valvetrain. The head (or heads, if an engine has more than one bank of cylinders) is always directly above the cylinders.

Cylinder Liner- The circular housing that the piston moves in when the cylinder is not an integral part of the block. It's often made of iron, although there are other light-weight coatings that certain manufacturers apply instead including alusil and nikasil.  Also known as a "sleeve."

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D

dBA- A unit of measure for decibels, the measure of sound intensity or pressure. It is a logarithmic measurement; every 3dB increase represents a doubling of the sound pressure. The "A" in dBA indicates that the measurement was taken with an A-weighted scale; sound pressure varies across the audible spectrum, and the A-weighted scale approximates the human ear's sensitivity to various frequencies.

DCT or Dual-Clutch Transmission- A relatively new type of transmission that uses bevel gears like a manual transmission, but allows for fully-automatic operation like a traditional automatic and semi-manual driver-selected operation via paddle shifters or a shift lever.  DCTs do not have a clutch pedal, but do allow for greater driver involvement than do traditional automatics.  DCTs' advantages include very quick-shifting and greater efficiency than a traditional automatic, and, in some cases, fairly smooth operation.  However, as they are a relatively new technology and they are complex, their longevity is unproven, and in certain examples, their shifting can be jerky. 

de Dion Suspension- An independent suspension system in which the rear, driven wheels are bolted to a transverse, lightweight, rigid member. Power is delivered to the wheels by universal-jointed half-shafts attached to a body-mounted differential.

Dead Pedal- A footrest found to the left of the leftmost pedal, which provides a place for the driver to brace his left leg during hard cornering.

Detonation- A condition in which some or all of the unburned air-fuel mixture in the combustion chamber explodes spontaneously, set off only by the heat and pressure of the air-fuel mixture. Detonation, or "knock," greatly increases the stresses on the engine and depending on its severity, can lead to catastrophic engine failure.  Cars with high compression ratios running low octane gas are more prone to detonation.

Differential- A gearbox that splits torque fed into it to two outputs that can turn at different speeds.  Cars employ differentials along their drive axles to route power to the wheels and AWD/4WD vehicles use center differentials to split power between the front and rear axles.

Differential  / Rear end ratio- The ratio at which the output of the differential turns relative to its input.  Generally, different differential / rear end ratios are optional on SUVs and pickups, as they allow improved acceleration and improved towing at the expense of fuel economy.

Direct Injection - Sometimes referred to as "DI", is a type of fuel injection system that injects fuel directly into the engine's combustion chamber, allowing the fuel spray to cool the charge in the combustion chamber.  This in turn allows a higher compression ratio, as the cooling effect staves off detonation, and results in more torque and power, usually made available throughout the engine's rev range.

Disc Brakes- Brakes that consist of a metal or ceramic disc that rotates with a wheel speed, straddled by a caliper that can squeeze the surfaces of the disc near its periphery. Disc brakes, which are virtually ubiquitous on new card, provide a more linear response and operate more efficiently at high temperatures and wet conditions than drum brakes.

DOHC- Double Overhead Camshaft: a DOHC engine has two camshafts in each cylinder head; one camshaft operates the intake valves, the other actuates the exhaust valves.

Downforce- In automotive vernacular, downward air pressure that pushes the car to the road and increases the tires' grip and thereby improving handling.  Very few street cars produce downforce, although race cars are commonly designed to do so.

Drag Coefficient- A dimensionless measure of the aerodynamic sleekness of an object. A sleek car has a drag coefficient, or "Cd," of less than 0.30; a square, flat plate's is 1.98.

Drivability- The general qualitative evaluation of a powertrain's operating qualities, including idle smoothness, cold and hot starting, ability to pull from low rpm, throttle response, power delivery, and tolerance for altitude changes.

Driveline- Everything in the drivetrain, less the engine and the transmission.

Driveshaft- The shaft that transmits power from the transmission to the differential.

Drivetrain- All of a car's components that create power and transmit it to the wheels; i.e. the engine, the transmission, the differential(s), the hubs, and any interconnecting shafts.

Drum Brakes- A brake that consists of a shallow drum that rotates with the wheel. Curved brake shoes within the drum are pushed into contact with the inner periphery of this drum to provide braking.  Very few modern cars use drum brakes, although they were common in cars of the past.

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E

Engine Control System- A computerized brain, often called the ECU, that regulates an engine's operation by monitoring certain engine characteristics (rpm, coolant temperature, intake airflow, etc.) through a network of sensors and then controlling key variables (fuel metering, spark timing, EGR, etc.) according to preprogrammed schedules.

EPA Fuel Economy- Laboratory fuel-economy tests, last updated in 2008, administered by the Environmental Protection Agency using simulated weight and drag to re-create real driving conditions. Contrary to popular opinion, the EPA does not test each vehicle, but instead relies on manufacturers to administer the test protocol from most models.  The EPA only tests about 15% of all car models. 

European New Car Assessment Program (Euro NCAP)- A car safety performance assessment program based in Belgium and backed by several European governments.  Euro NCAP conducts crash testing based on an offset front impact test, a side impact test, a side impact pole test and a pedestrian safety test.  Further discussion of Euro NCAP is set forth in the Crash Tests discussion [Link]

Exhaust Manifold- The iron / steel tubing that gathers the exhaust gases from the engine's exhaust ports and routes them toward the catalysts and mufflers of the exhaust system. A manifold with free-flowing passages of a carefully designed configuration, called a "header," can improve breathing.

Exhaust Port- The passageway in the cylinder head leading from the exhaust valves to the exhaust manifold.

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F

Final-Drive Ratio- The reduction ratio, found in the drivetrain, that is furthest removed from the engine. Typically, the differential ratio.

Flat Load Floor- A feature in the cargo area of some minivans and SUVs, whereby the rear seats can be folded down to create a flat, unobstructed floor onto which one can load cargo.  This is in contrast to a load floor that has humps or protrusions caused by the folded rear seats, which can make loading cargo more difficult.

Floorpan- The largest and most important stamped metal part in a car's body.  The floorpan forms the floor and fixes the dimensions for most of the car's external and structural panels.

Fluid Coupling- Any device that transfers power through a fluid between its inputs and outputs. A fluid coupling basically consists of two fans in a sealed, oil-filled housing. The input fan churns the oil, and the churning oil in turn twirls the output fan. Such a coupling allows some speed difference between its input and output shafts.  The most common fluid coupling is the torque converter in cars with an automatic transmission.

Flywheel- A heavy disc attached to an engine's crankshaft to increase its rotary inertia, thereby smoothing its power flow.  Lighter flywheels allow engines to rev faster, at the cost of smoothness, and are sometimes incorporated in expensive sports cars.

Four Valves Per Cylinder- A valvetrain with a total of four valves in the combustion chamber, typically two intakes and two exhausts. Compared to the historically more common two-valve-per-cylinder designs, a four-valve layout offers improved high-rpm breathing.

Four-Wheel Steering- A steering system that steers the rear wheels as well as the fronts in the interest of improving handling and maneuverability.  Four-wheel steering was popular in Japanese sports cars of the 80s and 90s, but has fallen into disfavor due to complexity and weight.

Four-wheel-drive / 4WD – Commonly used interchangeably with all-wheel-drive, four-wheel-drive is a drivetrain configuration by which all four of a car's wheels are driven with power from the engine part-time (generally, when the driver so selects via a lever or switch).  In contrast, all-wheel-drive more commonly refers to a drivetrain configuration in which all four wheels of a car are only driven all of the time.

Fuel Injection- Any system that meters fuel to an engine by measuring its needs and then regulating the fuel flow, by electronic or mechanical means, through a pump and injectors. Throttle-body injection, which is rarely employed on new cars, locates the injector(s) centrally in the throttle-body housing, while port injection allocates at least one injector for each cylinder near its intake portDirect Injection locates the injectors such that they spray fuel directly into the combustion chamber.

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G

g- The unit of measure for lateral acceleration, or "road-holding." One g is equivalent to 32.2 feet per second per second, the rate at which any object accelerates when dropped at sea level. If a car were cornering at 1.0 g—a figure that very few production cars are able to approach—the driver's body would be pushing equally hard against the side of the seat as against the bottom of it.

Gearset- A group of two or more gears used to transmit power.

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H

Half-Shaft- Sometimes simply referred to as an "axle", an articulating, rotating shaft used in independent-suspension systems to transmit power from a differential to a wheel.

Handling- A general term covering all the aspects of a car's behavior that are related to its directional control.

Hands Free Calling - A technological feature that allows your cell / mobile phone to connect to the car's stereo system via Bluetooth and to use an in-car microphone and the stereo speakers to talk on the phone without holding it.  Hands Free Calling is not only convenient, but can be a very important safety feature, helping to minimize driver distraction.

Hatchback – A car with either 3 or 5 total doors.  A hatchback is sometimes known as a "two-box" design because the roof extends to the rear of the vehicle.  Hatchback vehicles do not have a trunk that is separate from the passenger compartment, but instead have a large rear door that opens to a cargo area that extends to the passenger compartment.  Hatchbacks offer greater cargo storage versatility than sedans or coupes.

Heel-and-Toe- A performance-oriented technique of down-shifting while braking that requires the driver to use all three pedals of a manual-transmission car simultaneously. To perform a heel-and-toe downshift, the driver brakes with the toe of his right foot and—while continuing to brake—uses the heel or the side of the same foot to blip the throttle and raise engine rpm as he downshifts. The left foot operates the clutch pedal in the normal fashion. This process is employed to smooth power delivery to the wheels and prevents the car's chassis from becoming upset mid-corner from spikes torque sent to the wheels.

HID / Xenon Headlights - High-intensity discharge headlights that produce a brighter, clearer light through the use of a metal halide lamp that contains xenon gas. HID headlamps have a more blue or white tint than traditional halogen lamps, and the light often seems more crisp.  Replacement costs for HID headlights are significantly more than for halogen lights.

Hill Assist – A technology that senses when a car is stopped on an incline and applies and holds the brakes until the driver launches the car.  This is a particularly useful feature for cars equipped with a manual transmission, as it prevents them from rolling back while the driver switches from neutral to first gear.

Hemi- A term used to describe any engine that has hemispherical combustion chambers in its cylinder head.  Although other designs can be just as, if not more, efficient as a hemi, the term has been popularized by Chrysler / Dodge for its line of V-8 engines.

Horsepower- Often abbreviated as "hp" or "bhp" (for brake horsepower), the common unit of measurement of an engine's power. One horsepower equals 550 foot-pounds per second, the power needed to lift 550 pounds one foot off the ground in one second: or one pound 550 feet up in the same time.

Hydraulic Lifter- A valve lifter that, using the engine's oil pressure, can adjust its length slightly: thereby maintaining zero clearance in the valvetrain. Hydraulic lifters reduce valvetrain noise and are maintenance-free.

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I

Independent Suspension- Any suspension in which the motion of a wheel is not directly affected by the vertical motion of the opposite wheel.  Commonly configurations on independent suspensions include control arm type suspensions, multi-link type suspensions and strut type suspensions.

Inherently Balanced Engine- Engine configurations that are balanced in the first and second order.  Inherently balanced configurations in modern cars and light trucks are: flat four-cylinder, flat six-cylinder, inline six-cylinder, V-8 and V-12.  These engine configurations have an advantage when compared to other configurations in terms of smoothness, although the smoothness of other configurations can been be improved through the use of balance shafts and other design features.

Insurance Institute for Highway Safety (IIHS)- A non-profit organization funded by auto insurers that works to reduce the number of vehicle crashes and the rate of injuries and property damage when they occur.  The IIHS conducts a variety of crash tests on new car models, including the Moderate Offset Impact Test, Small Overlap Offset Test, Side Impact Test and Roof Strength evaluation.  Further discussion of IIHS testing is set forth in the Crash Tests discussion [Link].

Intake Charge- The mixture of fuel and air that flows into the engine.

Intake Manifold- The network of passages that direct air or air-fuel mixture into the cylinders of an engine.  The flow typically proceeds from the throttle body into a chamber called the plenum, which in turn feeds individual tubes, called runners, leading to each intake port. Engine breathing is enhanced if the intake manifold is configured to optimize the pressure pulses in the intake system.  Many modern cars use light alloy (aluminum or magnesium) or plastic intake manifolds to save weight.  Plastic intake manifolds can sometimes become brittle over time and develop cracks.

Intake Port- The passageway in a cylinder head leading from the intake manifold to the intake valve(s).

Intercooler- A heat exchanger, resembling a radiator, that cools the air (or, in some installations, the intake charge) that has been heated by compression in a supercharger or turbocharger.

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J

Jounce- The motion of a wheel that compresses its suspension.

Jounce Bumper- An elastic cushion used to stiffen the suspension gradually as it approaches the end of its jounce travel.

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K

Kickdown- A downshift in an automatic transmission caused by depressing the throttle.

Knock Sensor- A sensor mounted on the engine that is designed to detect the high-frequency vibrations caused by detonation. By employing a knock sensor, a computerized engine-control system allows an engine to operate very near its detonation limit: thereby improving power and efficiency.  It also allows many modern engines that are recommended to use premium (high-octane) fuel to operate on regulate (87 octane) fuel without damage, although with reduced performance.

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L

Lateral Link- A suspension link that is aligned to resist sideways motion in a wheel.

Leading Link- A suspension link that is aligned to resist longitudinal motions in a wheel; it is mounted to the chassis behind the wheel.

Leaf Spring- A flat, flexible piece of bowed steel or composite material, made up of one or multiple elements that is primarily used in the rear suspensions of pickup trucks and some SUVs.  Leaf Springs can generally better cope with heavy loads than coil springs, but often provide poor ride quality.

Lift-Throttle Oversteer- A handling characteristic that causes the rear tires to lose some of their cornering grip when the throttle is released during hard cornering, generally as a result of weight shifting forward.

Limited-Slip Differential- A differential fitted with a mechanism that limits the speed and torque differences between its two outputs. Limited slip ensures that some torque is always distributed to both wheels, even when one is on very slippery pavement.  Limited-slip differentials are highly desirable in sports cars or high-powered cars where a lot of torque is sent to the drive wheels.

Line- The path through a corner that best accommodates a late braking point, a high cornering speed, and the fastest possible exit speed out of a corner.

Link- A suspension member that has a single joint at each end.

Live Axle- A rigid axle incorporating a differential and axle shafts to power the two wheels it is supporting, the opposite of an independent suspension.  Live axles are generally very durable and can provide for a great range of suspension articulation in four wheel drive vehicles, but impair ride quality due to their high unsprung weight and can lead to poor handling and a loss of grip on rough roads, as one tire's movement also effects the other tire. Live axles were common in the past, primarily in RWD cars and light trucks.  They remain on a few cars and many light trucks.

Locking Differential- A differential whose two outputs can be locked together, eliminating any differential action but maximizing traction under slippery conditions.  Locking differentials are desirable in four-wheel-drive / off-road vehicles, as they ensure that all wheels are delivering torque at all times.  They have very limited use on-road, as they impede turning / handling and increase tire wear.

Locking Torque Converter- A torque converter fitted with a locking clutch that can be engaged to eliminate the slip between the torque converter's input and output, thereby improving fuel efficiency and performance.

Loose- A slang term for oversteer.

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M

Main Bearings- The bearings in an engine block that support the crankshaft.

Magnetorheological Shocks- Shock absorbers that employ magnetorheological fluid (smart fluid that can vary in viscosity depending on electrical current), allowing the shocks' damping rate to be varied.  Such shocks can allow for very smooth ride quality while providing tight body control for good handling, when necessary.  They can however be very expensive.

Mid-Engine- A chassis layout that positions the engine behind the front axle but ahead of the rear axle.  Generally also means that the engine is behind the passenger compartment.

Minivan – A van-like vehicle that is somewhat smaller than a traditional full-size van and is build primarily for hauling up to 8 people.  Minivans are built on more car-like chassis than full-size vans and accordingly handle better and deliver better fuel economy than full-size vans.

Monocoque- A type of car body structure that derives its strength and rigidity from the use of thin, carefully shaped and joined panels, rather than from a framework of thick members. Also called "unit" or unitized construction.

Multilink Suspension- A rear suspension consisting of at least four links, or "arms," and no struts. Because multilink suspensions assign specific wheel-locating duties to each element, they provide great flexibility for optimizing both ride and handling.

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N

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O

On-Center Feel- The responsiveness and feel of the steering when the wheel is approximately centered. In a car with good on-center feel, the steering wheel tends to return to center when slightly deflected, assisting straight-line stability.

Opposite Lock- A technique in which the steering wheel is turned in the direction away from where the car is turning. Opposite lock is used to control a car when it is oversteering and its tail is swinging wide.

Overdrive- Any gearset in which the output shaft turns faster than the input shaft. Overdrive gears are used as the highest / top gears in most modern transmissions because they reduce engine rpm and improve fuel economy.

Overhead Cam- The type of valvetrain arrangement in which the engine's camshaft(s) is in its cylinder head(s). When the camshaft(s) is placed close to the valves, the valvetrain components can be stiffer and lighter, allowing the valves to open and close more rapidly and the engine to run at higher rpm. In a single-overhead-cam (SOHC) layout, one camshaft actuates all of the valves in a cylinder head. In a double-overhead-camshaft (DOHC) layout, one camshaft actuates the intake valves, and one camshaft operates the exhaust valves.

Oversquare- A description of an engine whose bore is larger than its stroke.

Oversteer- A handling condition in which the slip angles of the rear tires are greater than the slip angles of the front tires, i.e., one in which the tail swings wide. An oversteering car is sometimes said to be "loose," because its tail tends to swing wide.

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P

Paddle Shifters- Paddle shifter refer to the paddles or buttons on or behind the steering wheel that allow the driver to manually shift the gears of an automatic or DCT equipped car up or down.

Pitch- The rotation of a car about a horizontal axis, which causes its nose or tail to bob up and down.  Dive and squat are pitching motions.

Port Fuel Injection- A type of fuel injection system with at least one injector mounted in the intake port(s) of each cylinder.  Port fuel injection has largely supplanted throttle body fuel injection on modern cars, although it is now being supplanted by direct injection.

Pound-Feet- The unit of measurement for torque. One pound-foot is equal to the twisting force produced when a one-pound force is applied to the end of a one-foot-long lever.

Power- The rate at which work is performed. Power is proportional to torque and rpm and is measured in horsepower or watts.

Power Band- The subjectively defined rpm range over which an engine delivers a substantial fraction of its peak power. The power band usually extends from slightly below the engine's torque peak to slightly above its power peak.

Powertrain- An engine and transmission combination.

Profile- The aspect ratio of a tire.

Progressive-Rate Spring- A spring with an increasing spring constant. Progressive-rate springs become stiffer as they are compressed, unlike single-rate springs, which have a fixed spring rate.

Psi- Pounds per square inch, the common unit of measurement for pressure. Normal atmospheric pressure at sea level is 14.7 psi.  In the automotive context, pressure is often measured for tire inflation and for the amount of boost in a supercharged or turbocharged engine.

Push- A slang term for understeer.

Pushrod- In a valvetrain, pushrods are used to transfer reciprocating motion from the camshaft to a more distant part of a valvetrain, typically the rocker arms.  Pushrod motors, also known as "Overhead Valve" of "OHV" motors, were historically favored by American manufacturers.

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R

Rack-and-Pinion- A steering mechanism that consists of a gear in mesh with a toothed bar, called a ""rack."" The ends of the rack are linked to the steered wheels with tie rods. Rack-and-pinion steering is largely ubiquitous in cars and car-based SUVs and generally provides superior steering feel to Recirculating-ball steering, which is more commonly found on pickup trucks.

Rebound- The motion of a wheel that extends the suspension. The opposite of jounce.

Recirculating-Ball- A steering mechanism in which the steering shaft turns a worm gear that, in turn, causes a toothed metal block to move back and forth. Ball bearings in a recirculating track reduce friction between the worm gear and the block. As the block moves, its teeth rotate a gear connected to a steering arm, which then moves the steering linkage.  Recirculating-ball steering was common on cars prior to the 1980s and remains in many pickup trucks.

Redline- The maximum recommended revolutions per minute for an engine, indicated by a red line in a tachometer on a car's instrument panel.

Ride Height- The height of a car's body from the ground. This dimension can be used to measure the amount of suspension deflection or the height of the body from the ground.

Ride Steer- A generally undesirable condition in which a wheel steers slightly as the car's suspension compresses or extends. Also called "bump steer."

Rigid Axle- A simple non-independent suspension consisting of a rigid transverse member with wheel hubs solidly bolted to it. The axle can be attached to the body by leaf springs, or by a combination of suspension arms and links.

Roadholding- The ability of a car to grip the pavement. Technically described as "lateral acceleration," because cornering is actually a continuous deviation from a straight path. Measured in gs.

Roll- The rotation of a car's body about a longitudinal axis, felt as a lean or sway to the car's passengers.

Roots-type Supercharger- A positive displacement type supercharger that operates by pushing air through a pair of meshing close-tolerance lobes.  Roots-type superchargers are used on several new car models to boost efficiency and power of the engine.

Runflat tires - Tires that allow a car to continue to be driven at reduce speeds for limited distances after the tire loses pressure.  Runflats can be viewed as a safety feature because they prevent the car from having to be stopped in dangerous areas (ie, busy highways, etc.) and can get you home.  They can however have disadvantages, including significantly increase cost, poor ride quality and impaired handling.

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S

SAE: Society of Automotive Engineers- The professional association of transportation-industry engineers. The SAE sets most automotive-industry standards for the testing, measuring, and designing of automobiles and their components.

Screw-type (Lysholm) Supercharger- A positive displacement type supercharger that operates by pushing air through a pair of meshing close-tolerance screws similar to a set of worm gears.  Screw-type supercharges were used on a limited basis on recent cars, probably because of the high cost of the twin screws, and are not used on any current new production cars.  Also known as Lysholm superchargers after their inventor, Alf Lysholm.

Sedan- Generally refers to a fixed-roof car with at least four doors.  Sedans are usually differentiated from hatchbacks in that they have a trunk or cargo compartment separate from the passenger compartment.

Semi-Trailing-Arm Suspension- An independent rear-suspension system in which each wheel hub is located only by a large, roughly triangular arm that pivots at two points. Viewed from the top, the line formed by the two pivots is somewhere between parallel and perpendicular to the car's longitudinal axis.

Series (Tire)- The numerical representation of a tire's aspect ratio. A 50-series tire has an aspect ratio of 0.50.

Shift Gate- The mechanism in a transmission linkage that controls the motion of the gearshift lever.

Shock Absorber- In automotive terms, most often a device used to dampen suspension oscillations caused by bumps and potholes.  Shocks can be simple purely mechanical devices that arrest motion by limiting the flow of either a gas or liquid through a porous medium.  However, certain modern models feature electronic control of valving or magnetorheological fluid to vary a shock's dampening rate, thereby allowing for supple ride quality, but tight control of body motions for good handling when necessary.

Side-curtain airbags - Large airbags that deploy from a car's ceiling along the sides of the car. Side-curtain airbags significantly reduce injuries, particularly head injuries, in side impacts and rollovers.

Single-Rate Spring- A spring with a constant spring rate. For example, if a 100-pound force deflects the spring by one inch, an additional 100 pounds will deflect it one more inch, and so on until the spring either bottoms or fails.

Skidpad - A large area of smooth, flat pavement used for various handling tests. Roadholding is measured by defining a large-diameter circle on the skidpad and measuring the fastest speed at which the car can negotiate the circle without sliding off.

Slip Angle- The angular difference between the direction in which a tire is rolling and the plane of its wheel. Slip angle is caused by deflections in the tire's sidewall and tread during cornering. A linear relationship between slip angles and cornering forces indicates an easily controllable tire.

SOHC- Single overhead camshaft: SOHC engines use one camshaft in each cylinder head to operate both the exhaust valves and the intake valves.

Space Frame- A particular kind of tube frame that consists exclusively of relatively short, small-diameter tubes. The tubes are welded together in a configuration that loads them primarily in tension and compression.

Spoiler- Theoretically, an aerodynamic device that changes the direction of airflow over a car in order to reduce lift or aerodynamic drag and/or improve engine cooling.  Most spoilers on cars are decorative and not functional.

Sport Utility Vehicle / SUV – A general term for a vehicle with its roof extended rearward toward the end of the vehicle, like a station wagon, that has a taller stance than a car / station wagon.  SUVs usually feature four-wheel-drive or all-wheel-drive.  SUVs were initially truck based vehicles, although car-based SUV-like vehicles have emerged.

Squat- The opposite of dive, squat is the dipping of a car's rear end that occurs during hard acceleration. Squat is caused by weight transfer from the front to the rear suspension.

Stability Control - A system that detects when a car is skidding selectively applies individual brakes to keep the  car on the driver's intended path.  It is standard on all 2012 models by federal regulation, but was not so in prior years.

Steering Feel- The general relationship between forces at the steering wheel and handling. Ideally, the steering effort should increase smoothly as the wheel is rotated away from center. In addition, the steering effort should build as the cornering forces at the steered wheels increase. Finally, the friction built into the steering mechanism should be small in comparison with the handling-related steering forces.

Steering Response- A term to describe how responsive a car feels to steering inputs.

Stop / Start System- A system that shuts down a car's engine when the car is stopped, for instance at a red light, to save fuel.  Stop / Start systems automatically and instantaneously restart the engine when the driver's foot moves from the brake pedal to the gas pedal.  Stop / Start systems can save significant amounts of fuel in city driving, although this is not reflected in the EPA estimated fuel economy on the window sticker because the EPA test does not include red lights in its city test.  Some Stop / Start systems operate seamlessly, whereas others are either slow to react or intrusive in their operation.

Straight-Line Tracking- The ability of a car to resist road irregularities and run in a straight line without steering corrections.

Stroke- The distance of a piston's travel in a cylinder.

Strut- A suspension configuration, sometimes called a MacPherson strut (named after its inventor), in which a reinforced shock absorber is used as one of the wheel's locating members.  Strut type suspensions are relatively cheap, simple and durable, although they can provide inferior ride quality and handling compared to control-arm or multi-link suspension configurations.  Strut type suspensions allow camber angle changes and sideways movement when the wheel moves, and further, can transmit noise and vibration directly into a car's bodyshell, providing a louder ride and "harsher" feel.

Supercharger- In modern automotive parlance, a mechanically driven air compressor used to force more air into an engine than it can inhale on its own, allowing it to make more power and torque.  Superchargers come in several configurations, including centrifugal, roots-type and screw-type.  Superchargers generally have quicker response times than turbochargers, but offer reduced efficiency gains compared to turbochargers because of their parasitic drag [link to turbo discussion].

Suspension articulation- The suspension's ability to flex.  Generally, greater suspension articulation is preferable in four-wheel drive / off road vehicles because it allows the suspension to deflect over large obstacles but maintain contact with the ground and traction.  Live axles often have greater suspension articulation than independently suspensions.

SUV- See Sport Utility Vehicle.

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T

Targa- A removable-roof body style popularized by Porsche that is similar to a convertible except that it incorporates a fixed, roll-bar-like structure running from side to side behind the front seats.

Throttle-Body- A housing containing a valve to regulate the airflow through the intake manifold. The throttle-body is usually located between the air cleaner and the intake manifold.

Throttle-Body Fuel Injection- A form of fuel injection in which the injectors are located at the engine's throttle-body, thereby feeding fuel to more than one cylinder. Such an arrangement saves money by using fewer injectors; but because it routes both fuel and air through the intake manifold, it eliminates some of the tuning possibilities offered by port fuel injection.  It is not employed on any new car models, but was common through 2000.

Toe-Control Link- A lateral link in a multilink suspension designed to control a wheel's direction as the suspension moves up and down.

Toe-In- The intentional nonparallel orientation of opposite wheels. Toe-in is measured by subtracting the distance between the front edges of a pair of tires from the distance between the rear edges of the same pair of tires. The toe-in dimension is positive when the fronts of the tires are turned toward the center of the car.

Toe Steer- The changes in the direction of a wheel that occur without driver steering input. Toe steer can be caused by ride steer or by deflections in suspension components caused by the stresses of cornering, accelerating, and/or braking on smooth and bumpy roads.

Torque- The rotational equivalent of force, measured in pound-feet.

Torque Converter- A fluid coupling employed in most automatic transmissions drivetrains.  Through the use of a stator, torque converters increase torque at the expense of rpm and efficiency.

Torque Steer- A tendency for a car to turn in a particular direction when power is applied. Torque steer is common in front-drive cars because reaction forces created in the half-shafts can generate uneven steering forces in the front tires.

Traction Control - A system that detects when a car's drive wheels are losing traction, or slipping, and takes a variety of measures (including braking and/or cutting engine power) to restore and maintain traction.

Trail-Braking- A driving technique in which the driver begins to brake before entering a turn and then continues to brake as he eases into the corner. As cornering forces build, the driver gradually feathers off the brakes, trading braking power for cornering grip. By increasing the vertical loading—and thus the traction—at the front tires, trail-braking can improve a car's turn-in.

Trailing Arm- A suspension element consisting of a longitudinal member that pivots from the body at its forward end and has a wheel hub rigidly attached to its trailing end. A sufficiently rigid trailing arm can provide all of a wheel's location. In that case it is similar to a semi-trailing arm, except that its pivot axis is exactly perpendicular to the car's longitudinal center line.

Trailing Link- A suspension link that is aligned to resist longitudinal motions in a wheel; it is mounted to the chassis ahead of the wheel.

Transaxle- A transmission and a differential combined in one integrated assembly.

Transmission- A gearbox with a number of selectable ratios, which allows a cars engine to effectively send power to the drive wheels, by matching the engine's rpm and torque to differing vehicle requirements. 

Tread Squirm- The flexibility in the tire tread between the surface of the tread and the tire carcass. Snow tires, with their small, deep, unsupported tread blocks, have a large amount of tread squirm.

Tumblehome- The term that describes inward curvature of a car's side glass as it approaches the roof, making the car narrower at the roof than at its waist. 

Turbocharger- An engine component powered by an exhaust-driven turbine that forces pressurized air into the engine, allowing the engine to make more power and / or achieve better fuel efficiency. Turbochargers always use centrifugal-flow compressors, which operate efficiently at the high rotational speeds produced by the exhaust turbine.

Turbo Lag- Within a turbocharger's operating range, lag is the delay between the instant a car's accelerator is depressed and the time the turbocharged engine develops a large fraction of the power available at that point in the engine's power curve.

Turn-In- The moment of transition between driving straight ahead and cornering.

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U

Understeer- A handling condition in which a car's front tires exceed their grip and push wide of the intended ark the driver intends to steer.  Technically, one would say the the slip angle of the front tires is greater than the slip angle of the rears.

Unitized Construction- A type of body construction that doesn't require a separate frame to provide structural strength or support for the car's mechanical components. A unitized body can employ monocoque construction, or it can utilize strong structural elements as an integral part of its construction.

Unsprung Mass / Weight- The mass of the suspension, wheels and portions of the drivetrain, and other components directly connected to them, rather than supported by the suspension.  Generally, greater unsprung weight hurts handling, grip and ride quality, because when a bump moves a wheel, the wheel initially deflects less rapidly and once it does, the shocks have greater difficulty arresting the motion of the wheel / suspension assembly.  Simple physics.

US New Car Assessment Program (NCAP)- A car safety performance assessment program conducted by the United States National Highway Traffic Safety Administration, an agency of the United States government.  NCAP conducts crash testing based on a full frontal impact test, a side impact test and a side impact pole test.  Further discussion of NCAP is set forth in the Crash Tests discussion [Link]

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V

Valve Lifter- Also called a "valve follower": the cylindrically shaped component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates. Most valve lifters have an oil-lubricated hardened face that slides on the cam lobe. So-called "roller lifters," however, have a small roller in contact with the cam lobe: thereby reducing the friction between the cam lobe and the lifter.

Valvetrain- The collection of parts that make the valves, which allow air into the engine, operate. The valvetrain includes the camshaft(s) and all related drive components, the various parts that convert the camshaft's rotary motion into reciprocating motion at the valves, and the valves and their associated parts.

Viscous Coupling- A particular kind of fluid coupling in which the input and output shafts mate with thin, alternately spaced discs in a cylindrical chamber. The chamber is filled with a viscous fluid that tends to cling to the discs, thereby resisting speed differences between the two shafts. Viscous couplings are used to limit the speed difference between the two outputs of a differential, or between the two axles of a car.

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W

Waste Gate- A valve used to limit the boost developed in a turbocharger. A waste gate operates by allowing some of the engine's exhaust flow to bypass the turbocharger's turbine section under certain conditions.

Wheel Hop- An undesirable suspension characteristic in which a wheel moves up and down so violently that it actually leaves the ground. Wheel hop can be caused by many problems, including excessive unsprung weight, insufficient shock damping, or poor torsional axle control.

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Y

Yaw- The rotation about a vertical axis that passes through the car's center of gravity.

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Z