Understand the markings on your tyres, recognise common wear patterns and know when to ask a tyre professional for help.
How to read a tyre size
The diagram shows 215/55 ZR17 94W. Here is how to read each part:
- 215 — Tyre width: The tyre's nominal width is 215 millimetres.
- 55 — Aspect ratio: The sidewall height is 55% of the tyre's nominal width, not 55 millimetres.
- ZR — Construction and speed designation: R identifies radial construction. Z indicates a high-speed tyre category; use the final speed-rating letter for the tyre's specific speed rating.
- 17 — Rim diameter: The tyre fits a wheel with a 17-inch rim diameter.
- 94 — Load index: This code identifies the tyre's load-carrying capacity. It is an index, not a weight in kilograms.
- W — Speed rating: This letter identifies the tyre's speed category. It is not a recommendation to drive at that speed.
These markings describe the tyre's size and ratings, but do not by themselves confirm suitability for your vehicle. Check your vehicle manufacturer's requirements before choosing a replacement.
Why tread matters
Tread grooves help manage water between the tyre and road. As tread wears, wet-weather performance can change. Check several points across each tyre and around its circumference, not just one easily visible spot. Wear indicators can help identify worn tread, but they are not a substitute for a full condition check.
Reference: NZ Transport Agency Waka Kotahi — Tyres. Infographics prepared by AMPEDTYRES based on this guidance.
Understanding tread patterns
Tread designs differ in both layout and intended use. These examples show the features to look for. Always follow the tyre's sidewall mounting markings rather than judging fitment from the pattern alone.
Symmetrical tread
Symmetrical tyres have a similar tread layout across both halves. Repeating ribs and grooves create a consistent pattern. Symmetry alone does not tell you whether a tyre has a specified rotation direction, so check its markings.
Asymmetrical tread
Asymmetrical tyres use different inner and outer tread zones, as shown by the differing patterns across the centre tyre in the comparison. Mount these tyres with the side marked OUTSIDE facing outwards and the side marked INSIDE facing inwards.
Directional tread
Directional designs often have V-shaped or arrow-like grooves and must roll in the direction indicated by the rotation arrow on the sidewall. Do not use the tread's appearance alone to decide the mounting direction.
Highway-terrain and all-terrain
Highway-terrain tyres generally have a more closely spaced, road-oriented tread. All-terrain designs generally have larger blocks and more open spaces between them. These categories describe intended use, rather than whether a tread is symmetrical, asymmetrical or directional. Choose for the roads and conditions you regularly drive, and confirm suitability for your vehicle.
When to get your tyres checked
Seek professional advice if you notice cuts, cracking, bulges, exposed reinforcement, recurring pressure loss or uneven wear. Vibration or a change in handling also deserves attention. A damaged tyre may be unsafe even when it still has plenty of tread.
A simple tyre check
- Confirm the size and ratings against your vehicle's specifications.
- Check cold tyre pressures against the vehicle placard or handbook.
- Inspect visible tread and sidewalls for wear or damage.
- Have anything unusual assessed before continuing to use the tyre.