IT’S THE LAW
A TYRE placard with available tyre sizes and minimum speed and load ratings has to be fitted to all vehicles to meet Australian Design Rules. These are the correct tyres for your vehicle, although there are a few exceptions (as we will explain). On most four-wheel drives, you’ll find the tyre placard on a door jamb or glovebox lid.
Always make sure load ratings meet or exceed the minimum for your vehicle, because you could be faced with a fine or, even worse, a tyre blow-out. And, if the tyres contributed to the crash, your insurance mightn’t cover you.
Wider rims and tyres are often a good thing, but to stay legal the tyres can’t be wider than the guards. Too-wide tyres can rub against brake lines, the suspension or guard lips, and none of this will end well. The wider tyres spray mud and water everywhere, too. Fit flares and – if needed – trim the guards.
You might have no choice but to fit bigger tyres because of a limited range of sizes, or because you want to increase ground clearance with a taller tyre. You don’t have to stick with the tyre sizes on the placard, but you do need to keep the overall rolling radius to a maximum 50mm over standard to stay legal. The 50mm is for total ride height change, so keep that in mind if you have (or are getting) a lift kit.
Most tyre manufacturers list the overall rolling radius of their tyres, so it’s pretty easy to work out what percentage a certain size is over your four-wheel drive’s standard boots.
You’ve got wriggle room with speed rating, too. The law allows lower-speedrated tyres for ‘off-road’ vehicles. That minimum is N (140km/h). Don’t be tempted to drive over those rated speeds on unrestricted NT highways, because you’re heading for a tyre blowout and a nasty crash. The tyres aren’t built to go that fast for very long.