Spoiler – An aerodynamic device, normally on the rear of the vehicle, that changes the direction of airflow in order to reduce lift
aerodynamic drag. A spoiler either reduces drag or create a downward force on the car. It is called a spoiler because it “spoils” the
normal air flow over the car.
Steering Ratio – A predetermined ratio of the steering gears. Usually, the lower the steering ratio, the quicker the response.
Stroke – The distance the piston travels from bottom dead center to top dead center within the cylinder.
Suspension System – Includes, springs, shock absorbers / struts, and linkage used to suspend a vehicle’s frame, body, engine and
drivetrain above the wheels.
Tachometer – An instrument for measuring the speed of the engine crankshaft in revolutions per minute (RPM).
Throttle-Body – Throttle-Body Fuel Injection is a type of Electronic Fuel Injection which positions the injector(s) centrally in a throttle-
body housing. This housing contains a valve to regulate the airflow through the intake manifold.
Tire Ratings – Tires are rated by load capacity, size and speed capacity. For example, a P225/50VR16 printed on the side of the tire
means: P = P-metric (Passenger type tire)
255 = Section Width (255 mm)
50 = Aspect Ratio (tire height/section width)
V = Speed Rating
R = Type of Ply (Radial)
16 = Wheel Diameter (16 inches)
Tire and wheel dimensions are the first point of information in any discussion of size and capacities. Among the other terms used to
describe tires are tread, shoulder, carcass, sidewall, bead seal, bead seat, tire diameter, aspect, ratio, speed rating and section width.
Toe In – The amount by which the front of a front wheel points inward or outward. A slight amount of toe in is usually specified to keep
the front wheels running parallel on the road by offsetting other forces that tend to spread the wheels apart.
Torque – A force that produces a twisting or rotating motion.
Torsion Bar – A long straight bar fastened to the frame at one end and to a suspension part at the other. In effect, a torsion bar is
merely an uncoiled spring, and spring action is produced by twisting the bar. The main advantage of the torsion bar over the coil
spring in the front suspension is the ease of adjusting the front suspension height.
Traction Control – Traction Control helps provide smoother, more controlled acceleration by reducing the amount of wheel spin
during reduced traction conditions. Traction control utilized the vehicle’s anti-lock braking system and is usually activated only at low
Turbocharger – Rotary compressor or pump that pressurizes engine air intake. It is driven by the flow of exhaust gases. The
increased pressure forces more air into the cylinder that it could normally draw, allowing the engine to burn more fuel and in turn
produce more power.
Undercoating – The application of a sound-deadening and / or rust-inhibiting chemical, wax or sealer to the underside of a vehicle.
Unibody Construction – A type of body construction that does not require a separate frame to provide structural strength or support for
the vehicle’s mechanical components. Also called “unitized”.
Valve – A device that can be opened or closed to allow or prevent the flow of a liquid or gas from one place to another. Most internal
combustion engines use intake and exhaust valves to allow fuel /air mixture in the cylinders and to exhaust burnt gases. Some
engines have four valves per cylinder, which increases total valve area for increased efficiency and performance.
Valve Train – The collection of parts that make the valves operate, allowing fuel intake, compression and exhaust. Includes the
camshaft(s) and all related drive components, and the various parts that convert the camshaft’s rotary motion into reciprocating
motion at the valves.