sedan: as used by Car and Driver, the term "sedan" refers to a fixed-roof car with at least four doors or any fixed-roof two-door car with at least 33 cubic feet of rear interior volume, according to measurements based on SAE standard J1100.

semi-elliptic leaf spring: a slightly curved leaf spring that is attached to a car's body at its ends and to a suspension component near its middle. One of the two body attachments is a shackle, which allows for changes in the spring's length as it flexes up and down.

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. The shift gate is usually an internal mechanism; however, in some transmissions: including Ferrari five-speeds and Mercedes-Benz automatics : the shift gate is an exposed guide around the shift lever.

shock absorber: a device that converts motion into heat, usually by forcing oil through small internal passages in a tubular housing. Used primarily to dampen suspension oscillations, shock absorbers respond to motion; their effects, therefore, are most obvious in transient maneuvers.

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 (Car and Driver uses 300 feet) 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.

slushbox: A slang for an automatic transmission.

SOHC: single overhead camshaft: an SOHC engine uses 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: an aerodynamic device that changes the direction of airflow in order to reduce lift or aerodynamic drag and/or improve engine cooling.

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

steering axis: the line that intersects the upper and lower steering pivots on a steered wheel. On a car with a strut suspension, the steering axis is defined by the line through the strut mount on top and the ball joint on the bottom.

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 gain: the relationship between yaw and the steering wheel's position and effort. All three should be proportional and should build up smoothly.

steering geometry: the group of design variables outside the steering mechanism that affect steering behavior, including camber, caster, linkage arrangement, ride steer, scrub radius, toe-in, and trail.

steering response: a subjective term that combines steering feel and steering gain.

straight-line tracking: the ability of a car to resist road irregularities and run in a straight line without steering corrections.

stroke: The distance between the extremes of a piston's travel in a cylinder.

strut: a suspension element in which a reinforced shock absorber is used as one of the wheel's locating members, typically by solidly bolting the wheel hub to the bottom end of the strut.

sump: the space in the engine block under the crankshaft into which the oil drains from its various applications.

supercharger: an air compressor used to force more air into an engine than it can inhale on its own. The term is frequently applied only to mechanically driven compressors, but it actually encompasses all varieties of compressors-including turbochargers.

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