Each tyre has standard markings that allow you to pick the right type for your car. It's a confusing mix of letters and numbers, and of measurements in mm and inches. Here's what it all means.

Size and speed ratings

All new tyres are marked with a size and speed rating. Our photo shows one marked 185/65R14 86H.

Here's what this means...

Symbol What it means
P Passenger tyre (not always shown).
185 The tyre width (across the tyre) in millimetres when fitted to the correct rim and inflated. A larger number means a wider tyre.
65 The profile or aspect ratio. In this case, the height is 65 percent of the width.
R Radial construction.
14 Rim diameter (inches). This can be metric, but very rarely.
86 A load index, which allows you to calculate the maximum load from a table. Tyre dealers have copies. 86 means this tyre can support a maximum load of 530kg. Not always shown on older tyres.
H The speed rating. This is the maximum speed the tyre will withstand at the rated load, in this case 210km/h. Speed ratings are typically from Q (160km/h) to Y (300km/h). Retreads have the speed rating removed, but those made to NZS 5423 are capable of speeds of at least 100km/h.

Older tyres may have the figures and letters in a different order (185 SR13) but they mean the same thing. Use the size and speed ratings when checking prices, to ensure you are comparing like with like. Replacement tyres should always have the same or better ratings.

What's the use of all this info? To keep the tyre grip evenly balanced when cornering, a car must have the same size and type of tyre on the left and right wheels on an axle (and usually the same size all round). Marking the size means WOF inspectors can easily check that your car has the right-sized tyres.

It also helps you. When you're looking for the best price on a replacement tyre you need to be able to quote the size (and sometimes the load and speed ratings).

Tread Wear Indicator
Tread wear indicator

The triangle on the sidewall points to a small bar in the tread grooves (pictured, right), which shows the minimum tread depth. The letters "TWI" or the maker's logo are alternative sidewall markings for the indicator.

Standard markings

Standard markings can reveal the tyre's origin. All tyres (except some Australian-made ones) should have at least one of these marks.

Symbol What it means
E European, plus an approval number.
DOT American, plus an approval number.
JIS Japanese.
NZS 5453 New Zealand Standard for locally made tyres (though tyres are no longer made in New Zealand).

There may also be information about the construction: number of plies and ply material, tubeless rating and information about suitable uses, or how to correctly mount the tyre (see Directional tyres).

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