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Know Your Tyres

Important information about car tyres

An important part of your vehicle’s road-handling capability is directly related to the tyres and their condition. Drivers need to check their tyres, tyre pressure and tread regularly. Tyre rotations should be done about every 5 000km to 10 000km.

Ensure that your tyre pressure is checked weekly. Also check for wear and bald spots on your tyres. When taking a trip with a fully loaded vehicle, look at the pressure table in the door of your vehicle or manufacturer’s manual to see what tyre pressure is needed for the estimated load and number of passengers.

Monitoring the tyre’s tread depth will ensure that the vehicle has good handling. And in the wet, proper tread will ensure that water is funneled and disbursed from underneath the tyres. It will also reduce hydroplaning.

Because pressure gauges at garages can vary, where possible, try to use the same garage each week to check the tyre pressure. Extreme weather also affects tyre pressure, hot weather can increase tyre pressure.

Rotating your tyres (front to back) can ensure that the tyres wear more evenly. Your vehicle’s manufacturer has specific recommendations for correct tyre rotation. Speak to an expert at your nearest AutoZone store for advice.

Low tyre pressure can also result in reduced fuel efficiency and excessive heat build- up, leading to tyre damage or blow outs. Regularly inspect the tyres for signs of excessive or uneven wear, especially inside where the tread is not easily visible.

What All the Numbers Mean

The small print on a tyre’s sidewall has a significant meaning

Tyre Type

The P designates that the tyre is a passenger vehicle tyre. Some other designations are LT for light truck, and T for temporary or spare tyre.

Tyre Width

The “235” is the width of the tyre in millimeters (mm), measured from sidewall to sidewall.

Aspect Ratio also known as profile

This number indicates the height of the tyre from the rim to the top of the tread. This is described as a percentage of the tyre width. If the aspect ratio is 75, the tyre’s height is 75 percent of its width. The smaller the aspect ratio, the wider the tyre in relation to its height.

Tyre height = 235 x 75 percent = 176.25 mm
Then we add twice the tyre height to the rim diameter.

High-performance tyres usually have a lower aspect ratio than others. This is because tyres with a lower aspect ratio provide better lateral stability. When a car turns at a corner, lateral forces are generated and the tyre must resist these forces. Tyres with a lower profile have shorter, stiffer sidewalls so they resist cornering forces better.

Tyre Construction

The R designates that the tyre was made using radial construction. This is the most common type of tyre construction. Older tyres were made using diagonal bias (D) or bias belted (B) construction. Traction: Tyre traction is rated AA, A, B or C, with AA at the top of the scale. This rating is based on the tyre’s ability to stop the vehicle on wet concrete and tar.

Temperature

The tyre temperature ratings are A, B or C. The rating is a measure of how well the tyre dissipates heat and how well it handles the buildup of heat. The temperature grade applies to a properly inflated tyre that is not overloaded. Under inflation, overloading or excessive speed can lead to more heat buildup. Excessive heat buildup can cause tyres to wear out faster, or could even lead to premature tyre failure.

Load Ratings

The load rating is a number that correlates to the maximum rated load for that tyre. A higher number indicates that the tyre has a higher load capacity. The rating “105,” for example, corresponds to a load capacity of 924 kg. A separate note on the tyre indicates the load rating at a given inflation pressure.

Speed Rating

The letter that follows the load rating indicates the maximum speed allowable for this tyre (as long as the weight is at or below the rated load). For instance, S indicates that the tyre can handle speeds up to 180 kph.