legal tyre size calculator australia

Chasing a legal tyre size calculator in Australia? Sensible move, because the rules aren’t one-size-fits-all—there’s a patchwork of state regs built atop the national NCOP (VSB 14) framework.

Use a calculator to compare overall diameter/rolling circumference and estimate speedometer change, but legality also hinges on keeping the placard’s load and speed ratings, preserving proper clearance (no rubbing at full lock or full compression), and ensuring the tread sits under the guards.

Your speedo must comply with ADR 18: it can over-read, but it mustn’t under-read, so big diameter jumps are a no‑no.

If you wander far from factory sizes, you may need certification and a polite chat with your insurer; calculators guide you, your state’s VSI/registration authority decides. Measure with the calculator, then verify against your state rules and the tyre placard before you go shopping.