Formula One glossary

I-head engine

An engine where both intake and exhaust valves are placed directly over the piston. The cam is located in the block and the valves are activated by pushrods and rocker arms. Also called "overhead-valve engine" or "valve-in-head engine".

Ignition

A process which initiates the combustion of the compressed air/fuel mixture in the combustion chamber. In a spark-ignition engine, the mixture is ignited by an electric spark; in a diesel engine, the self-igniting mixture must be preheated by glow plugs when a cold start is performed.

Ignition timing

It is important that the spark coming from the spark plugs ignites the air-fuel mixture at the correct moment determined by the manufacturer of the engine. Often this is a few degrees before top dead center (BTDC). Suppose the specs indicate that it should be set at 5 degrees BTDC, but in actuality it is set at 6 degrees. In that case, the timing is advanced. If it were set at 4 degrees, the timing is retarded. Incorrect ignition timing may result in poor performance and excessive fuel consumption.

Imbalance

A lack of balance due to uneven weight distribution. Improper wheel balance due to uneven weight distribution on the tire and wheel assembly is one of the most common causes of vibration. When one side of the tire and wheel assembly is heavier than the other, centrifugal forces try to throw the heavy area outwards as the wheel turns.

Inboard brake

Most cars have the brakes associated with the wheel. Drum brakes, for instance, are located in the wheel hub itself. Disc brakes are found attached to the wheel. However, inboard brakes are not located within the wheel. Instead, they are found attached to the differential housing or axle shaft. Thus they are generally located only on the rear of the vehicle. Inboard brakes mean a reduction in unsprung weight and usually better cooling.

Inertia

That force which tends to keep a stationary object from being moved, and tends to keep a moving object in motion. Some effort is needed to get the object moving if it is stopped, and to stop an object if it is moving.

Installation lap

A necessary lap on arrival at a circuit to test functions such as throttle, steering and brakes before returning to the pits - without crossing the finishing line.

Intercooler

An intercooler is a special radiator through which the compressed air passes to cool it off before it enters the cylinder. This can only be found in turbocharged engines, as compression heats the air up, and normally aspirated engines do not have to cope with extra warmed up air.

Intermediate tyre

A tyre that has more grooves and a more treaded pattern than the dry weather tyre, but fewer than a full wet-weather tyre, and is used in mixed conditions.

Isomer

Compound whose molecule contains the same species and number of atoms as another, but is different from the other in its molecular structure.