Tyre size calculator
Everything your tyre size is telling you.
Minimum tread depth and when to replace
1.5 mm
Legal minimum in Australia
The tread-wear indicator bars moulded into the grooves sit at this depth. At 1.6 mm in the UK and EU, 2/32 in (1.6 mm) in most US states.
3 mm
Replace for the wet
Below about 3 mm, stopping distances in the wet grow quickly as grooves can't clear water. Most tyre makers suggest replacing here.
4 mm
Winter tyres
Winter and all-weather tyres lose much of their snow grip below about 4 mm.
Tyre size questions
How do I read a tyre size?
Take 245/40 ZR18 97Y. 245 is the width in millimetres. 40 is the sidewall height as a percentage of that width. Z means rated above 240 km/h and R means radial construction. 18 is the rim diameter in inches. 97 is the load index (730 kg per tyre) and Y is the speed rating (up to 300 km/h).
Where do I find my tyre size?
On the sidewall of your current tyres, and on the tyre placard, usually in the driver's door jamb. The placard is the authority: it lists the sizes your car was approved with and the minimum load index and speed rating.
What is the minimum legal tread depth in Australia?
1.5 mm across the tread, which is where the tread-wear indicator bars moulded into the grooves sit. The UK and EU use 1.6 mm, and most US states 2/32 inch.
How often should tyres be replaced?
By tread, at the legal minimum at the latest (1.5 mm in Australia) and ideally around 3 mm, where wet braking starts to fall away. By age, most tyre makers recommend a yearly inspection from five years old and replacement at ten years regardless of tread, including the spare.