An instrument for measuring the rotary speed of the engine crankshaft, a gear, shaft, etc. in revolutions per minute (RPM). Tappet A pivoting actuator than opens and closes cylinder valves.

The part of an exhaust system where exhaust gasses exit the car body.

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.

Information sent from the vehicle manufacturer to a dealer's service department that describes change s in a maintenance or repair procedure.

An emissions control part that opens or closes depending on engine temperature.

A simple but critically important device that regulates temperature. In a cold engine, it closes to block the flow of coolant going to the radiator (thus providing faster warm-ups), then opens when the coolant reaches a specific temperature. A valve, located in the cooling system of an engine, which is closed when cold and opens gradually in response to engine heating, controlling the temperature of the coolant and rate of coolant flow.

The throttle regulates the amount of air/fuel mixture that is fed to the engine.

An emissions system device that monitors the position of the throttle plate.

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 plenum.

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.

Part of the steering system, the tie rod connects the wheels to the rest of the steering system.

Timing refers to when the spark ignites the air/fuel mixture. Timing needs to be set exactly right for an engine to run correctly.

Timing belts are rubber belts that connect an engine's camshaft to its crankshaft. If a timing belt breaks, these two components will go out of synch, causing potentially significant engine damage.

Tires that provide acceptable traction for winter snow and slush driving conditions, without excessively compromising dry and wet traction.

(e.g. 60-series tires)Tire aspect ratio is refers to the ratio between the tread(section) width and the sidewall. For example, a 205/50-15 tire would have a sidewall height of 0.50 x 205 or 102.5 mm. Lower aspect ratios(e.g. 40-series) provide superior handling at the cost of increased ride harshness. Tires, M+S rating Tires especially designed to perform well in mud and snow. M+S tires are usually superior to all-season tires under these conditions. The tradeoff is often higher noise and reduced tread life.

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 (255mm) 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. The tire treadwear rating gives an approximate idea of the expected usable life of the tire. A tire rated 300 will probably last 50% longer than one rated 150. Note that each tire manufacturer has its own rating methods. So a Goodyear tire rated at 300 will not necessarily give the same tread life as a Michelin tire rated at 300. It may last longer under the same conditions or it may not. The treadwear number is most relevant when comparing tires by the same manufacturer. The 'AB' designation indicates wet traction and temperature resistance, respectively. Wet traction ratings are AA, A, B, and C. 'AA' is the best. 'C' is the worst. Temperature resistance ratings are A, B, and C. 'A' is best. 'C' is worst. The temperature resistance rating signifies a tire's heat dissipation capabilities. Excess heat leads to premature tire failure, so cooler running tires last longer.

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.

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

The intentional nonparallel orientation of opposite wheels. The amount by which the front of a front wheel points inward or outward. 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. 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. When the leading edges of a pair of wheels are closer together than the trailing edges. See also Toe-Out.

When the leading edges of a pair of wheels are farther apart than the trailing edges.