Do you know what those markings on the sides of your tyres mean? If you do, that's great. If you don't, you need to read on…
A lot of us rely on trusted experts to deal with our tyres without ever understanding exactly what connects us to the road. That's just lazy! Especially so when you consider the fact that tyres are the most important link between our vehicle and the road.
Tyres play an integral role in road safety and many crashes and near misses can be attributed to tyres that are badly worn, made of cheap, inferior materials, or not suitable for the type of driving you do.
If you've never taken the time to learn more, or never even realised you need to know more, there's never been a better time to dive into what those numbers and ratings mean.
For those planning to hit the slopes this ski season, you need to know how to read your tyre size. Why? Snow chains. Legally all vehicles entering an alpine resort between 1 June - 31 October must carry & fit chains when directed.
Whether you plan to hire or buy chains the first thing you need to know is the correct size, and it's better and easier to decipher these during the daylight rather than by torchlight in the dark, cold and wet outside a chain hire location on the way to the slopes.
We'll start with the basics; that jumble of letters and numbers embossed on the sidewall.
Everything is there thanks to an extensive document called ‘Vehicle Standard (Australian Design Rule 23/02 - Passenger Car Tyres) 2007’, which is an addition or amendment to s7 of the Motor Vehicle Standards Act 1989.
According to the legislation, the numbers and letters have to be there to prove the tyre meets accepted National Standards.
Aside from being an offence under the Act, if you import or buy tyres that aren't compliant (that is, missing these markings) and fit them to your vehicle, you'll also void your insurance policy.
If you take a look at the tyre of the Audi A1 (pictured above), among other markings you'll see 215/45R16 90V embossed into the rubber. Further adding to the confusion is the fact that some of the parameters, like the tyre width for example, are measured using the metric system, while others like the rim diameter, use the imperial system.
Here's the breakdown:
215 - the width of the tyre (in millimetres)
45 - the aspect ratio or the height of the sidewall from the wheel rim. This figure is the percentage of the width, in the Audi A1's case, 45% of 215mm = 129mm.
R - stands for radial ply construction. The other option is the older style bias ply construction, not commonly used anymore although you can find these tyres on older, classic vehicles.
16 - the wheel rim diameter in inches.
90 - the load rating or load index. This is a series of numbers (0-279) that correspond to the maximum load of each tyre in kilograms. In this case, 90 = 600kg. Here's some of the other load ratings you might find on passenger tyres: 81=462kg, 82=475kg, 85=515kg, 86=530kg, 87=545kg, 90=600kg, 92=630kg, 95=690kg, 96=710kg.
V - the speed symbol. This lets you know the safe upper speed limit of the tyre with the maximum load. The letters N, P, Q, R, S, T, U, H V, Z, W & Y mean 140, 150, 160, 170, 180, 190, 200, 210, 240, 240, 270, 300km/hr respectively.
The load rating and speed limit go hand in hand; in our example the tyres can handle 240km/h with 600kg of load per tyre.
It's particularly important to understand the load capacity and speed limitations of your tyres, and if in doubt always ask a professional. So there you have it. Not that complex after all is it?