Tyre sizes can be confusing.  Gone is the 31/10.5R15......now its 265/75R15

To understand and calculate your tyre size.....

Example 285/70R17LT

• 285 is the tyre width
• 70 is an aspect ratio, as a percentage of tyre width
• R denotes Radial construction
• 17 is the wheel diametre in inches
• LT denotes Light Truck construction

So....

• 70% of 285 = sidewall height (199.5mm)
• 199.5mm x 2 = 399mm
• 399mm + 432mm (17inches) = overall tyre height
• Tyre diametre is 831mm

Load and speed ratings are usually on the tyre bead area next to the tyre size.

Example 285/70R17LT  121/118Q 10PR Load Range E

• 121 single tyre load rating (1450kg)
• 118 dual tyre load rating (1320kg)
• Q denotes speed rating (160kmh)
• 10PR denotes a nominal Ply Rating (not sidewall plys)
• Load Range E equates to the relevant Ply Rating

For Australian use in general, only the single tyre load rating is relevant.  Make sure your tyre of choice meets or exceeds the load rating on your vehicle placard.  Search "tyre load rating chart" for a complete list of figures.