Alignment
Alignment basically means that all four tyres are consistent with each other and are positioned to optimise contact with the road. It consists of three elements – caster, camber and toe.
Air Pressure
The pressure of the air inside a tyre. Tyre pressure is measured in psi (see psi).
Aspect Ratio
Aspect ratio is section height divided by section width and multiplied by 100. The higher the figure, the higher the tyre’s section height, the smoother the ride. The lower the figure, the greater a tyre’s section width and the safer the tyre – best for high speed cars.
Balancing
Balancing a wheel (or tyre) ensures that the weight is evenly distributed. This prevents vibration and uneven tyre wear.
Camber
Camber is the angle that the tyre tilts – 0 degrees means the tyre is perfectly perpendicular to the road. If it tilts in at the top towards the vehicle, the camber is negative. Positive camber is when the tyre tilts away from the vehicle at the top.
Casing
The casing of a tyre is the outside part of a pneumatic tyre (i.e. not the inner tube).
Cold Inflation Pressure
The pressure of a tyre before the vehicle is driven and the tyre is warmed up.
Innerliner
An innerliner is a lining inside a tyre that prevents air leaking.
Load Index
The maximum weight a tyre can safely carry.
Markings
Tyre markings are the symbols on a tyre’s sidewall to indicate (for example) load index.
PSI
PSI is ‘pounds per square inch’ and is a standard measurement of pressure. Basically, it’s the amount of force exerted over one square inch. Normal tyre pressure is 32 psi.
Rim
Rim and wheel are often used interchangeably – it is the part that the tyre sits on.
Rolling Resistance
The force required to maintain forward momentum in a straight line at a constant speed.
Run Flat Technology tyres
Run Flat Technology tyres are designed to withstand punctures, thereby allowing the driver to continue to drive even when the tyre is completely deflated. The safety benefits are that it avoids the need for drivers to stop by the side of the road to change tyres and giving drivers ample time to make it home or to the nearest tyre replacement centre, provided they drive within the accepted speed limit and safe distance.
Sidewall
The part of a tyre between the edge of the wheel and tread.
Sipes
Small slots in a tyre’s tread.
Speed Rating
The maximum speed a tyre can travel, corresponding to its load index.
Tyre
The rubber part that sits on the wheel.
Tyre Size
Tyre size is actually a set of numbers and letters that define a tyre’s specifications, such as section width (from sidewall to sidewall), aspect ratio, speed rating and diameter of the wheel the tyre is made to fit on.
Tread
The raised part of the rubber on a tyre.
Treadwear Indicator
Features built into a tyre to let the driver know that the tyre is worn sufficiently to necessitate changing.
Underinflation
When a tyre is not inflated enough – it can result in a shorter lifespan and reduce fuel economy. Steering and cornering will be negatively affected and rolling resistance will be increased.
Winter Tyres
Winter tyres are specifically designed to be used on winter roads – ice, snow and water.