Avon tyre shoulderThe shoulder of a tyre is the curved area joining the tread to the sidewall.

A tyre which is under-inflated will wear at the shoulders first. If only one shoulder is worn, it indicates a suspension or steering fault – either caused by wear or less than ideal geometry.

Damage to the shoulder of a tyre cannot usually be repaired.

Shoulder is also a term used in road design, and describes the area next to the carriageway – which is often either paved (hard shoulder) or grassed (soft shoulder).

Stoichiometric is the term given to an air to fuel ratio which gives the theoretically perfect balance of air and fuel.

In a petrol engine, the stoichiometric ratio is approximately 14.7 parts air to one part fuel (by weight).

If the air to fuel ratio is greater than the stoichiometric value, ie there is an excess of air, the mixture is lean. If the air to fuel ratio is less than the stoichiometric value, ie there is excess fuel, the mixture is rich.

Sidepod on Mercedes GP car

Sidepods are used on single-seater racing cars. Usually each sidepod will have an air intake at the front which will deliver cooling air to oil or water radiators within the sidepod.

On the ground effect F1 cars of the 1970s and 1980s the sidepods extended close to the ground and were venturi-shaped, with the gap between the sidepod and the ground sealed using a sliding or brush skirt.

A splitter is an aerodynamic device which produces downforce at the front of a car.

A splitter is a horizontal flat surface at the base of an airdam. Air encountering the airdam may be turned downwards, where it acts on the surface of the splitter and forces it down.

Uniroyal tyre on a wet road

Sizzle is a term used by engineers to describe a type of tyre noise which occurs on wet roads.

Sizzle is used by NVH engineers to describe the sound generated by the water as it is squashed between the tyre tread and the tarmac.

A similar sizzling sound can be generated on dry roads if the road surface is very smooth, due to air trapped in the tread of the tyre.