According to 2018 figures from the NZ Transport Agency, there were 32 fatal crashes over the previous three years linked to worn tyres. This is in addition to 464 tyre-related crashes which resulted in minor, serious or no injury.

The Motor Trade Association (MTA) says worn tyres have been linked to a growing number of crashes since the warrant of fitness system was changed in 2014 (up from 107 crashes in 2014 to 166 in 2017).

This has prompted the organisation to encourage vehicle owners to consider changing their tyres when they have 3mm of tread left, rather than the allowable depth of 1.5mm. MTA Chief Executive Craig Pomare says “At 1.5mm you have half the stopping distance as a new tyre in the wet.”

Many tyres have tread-depth indicators built into them, so you can easily see when a tyre has reached its minimum legal depth of 1.5mm. If you’re finding it difficult to locate the tread-depth indicators in your tyres, look for a small triangle icon, or the letters TWI (tread wear indicator) on the sidewall of the tyre.

So, whether you need new tyres because you’re a safety-conscious Kiwi, or you’ve taken your tyres to the line and failed your WOF, how do you go about deciphering all the tyre options out there?

What do all the numbers mean?

Tyre size is represented by a series of numbers and letters, which can be confusing. Let’s use a popular care tyre size – 205 55R 16 – to explain. These numbers can be found on the sidewall of a tyre and indicate the size and structure of a tyre.

205: This represents the tread width of a tyre, in millimetres. This is the part of the tyre that touches the road surface.
55: This is the aspect ratio, shown as a percentage. This represents the height of a tyre, measured from the bottom of the tyre tread to the rim.
R: This indicates that the tyre has radial construction.
16: This is the internal diameter, or rim size, measured in inches.

There may be other numbers, which indicate the load capacity and speed rating of a tyre.

What are the different types of tyres?

Symmetrical tyres

As the name suggests, this type has the same tread pattern on both sides of the tyre. These are the most common tyre fitted to compact and city cars and are available in smaller sizes such as 13, 14 and 15 inches. They represent good value for money and generally last longer than other types. They can also be fitted on either side of your car and rotated without any risks. However, they are not designed for performance or sports cars.

Asymmetrical tyres

Unlike symmetrical tyres, asymmetrical tyres have a different tread pattern on the inside and outside of the tyre. The tread blocks on the outside are usually larger to give better grip when cornering, while the grooves on the inside are designed to remove water on wet roads. This type of tyre is mostly available in larger sizes (17 inches and above) and are commonly fitted to middle to upper range and performance vehicles, as well as sports cars. These tyres are designed to fit on only one particular side of the tyre rim.

Space-saver tyres

Many modern, and particularly compact, cars are fitted with space-saver tyres that are lighter and smaller than standard full-size spare tyres. This is a cheaper option and allows more space in the vehicle boot. The idea with these tyres is to use them temporarily if you have a flat to get to a tyre shop that can replace or repair your proper tyre. These are only for use in an emergency and are not designed for use over long distances. Drive more carefully with a space saver tyre fitted and never go faster than 80km/h.