Car Tyres: Tread Depth, Pressure, and When to Replace — NZ Guide

Why Tyres Matter More Than Any Other Component

Your tyres are the sole connection between your car and the road. Every braking force, cornering force, and acceleration is transmitted through four contact patches roughly the size of your hand. Worn, underinflated, or damaged tyres compromise everything — stopping distances, wet-weather grip, fuel economy, and handling.

In New Zealand, tyre condition is one of the most common reasons for a WoF failure.

Legal Tread Depth in New Zealand

New Zealand law requires a minimum tread depth of 1.5 mm across the full width of the tyre, in a continuous band around the circumference. Most new tyres start with 7–8 mm of tread.

How to check:

• Use a tread depth gauge (available at auto parts stores for $5–$15)
• Look for the tread wear indicators — small raised bars moulded into the tyre grooves. When the tread is flush with these bars, the tyre is at or near the legal minimum
• Insert a 20-cent coin into a groove — if you can see the top of the numbers, the tyre is getting low

Recommendation: Replace tyres at 2–3 mm in NZ conditions. Wet roads are common across the country, and wet-weather grip deteriorates rapidly below 3 mm. Do not wait until you fail your WoF.

Tyre Pressure: Getting It Right

Correct tyre pressure is critical for safety, tyre life, and fuel economy. Your vehicle's recommended pressures are found:

• On a sticker inside the driver's door jamb
• In the owner's manual

Pressures are quoted in kPa (kilopascals) in NZ — common values are 200–240 kPa for passenger cars. Check pressure when the tyres are cold (not driven for at least two hours).

Check pressure monthly, and always before long trips.

Common Tyre Wear Patterns

Uneven wear tells a story — don't just replace the tyre without fixing the underlying problem, or the new tyre will wear the same way.

Tyre Types for NZ Conditions

For most NZ drivers in Auckland, Wellington, or Christchurch, quality all-season tyres are the best choice.

When to Replace Tyres

Replace a tyre if:

• Tread is at or below 1.5 mm (legal minimum) — ideally replace at 2–3 mm
• A sidewall bulge or blister is visible — indicates internal structure failure; replace immediately, do not drive
• A cut, gash, or tear in the sidewall — tyres cannot be repaired at the sidewall
• Age over 6–10 years — rubber degrades regardless of tread depth. Check the DOT code on the sidewall (last 4 digits = week and year of manufacture, e.g., "2420" = week 24 of 2020)

How Much Do New Tyres Cost in NZ?

Prices include fitting, balancing, and disposal of the old tyre. Budget brands are cheaper but wear faster; premium brands (Bridgestone, Michelin, Pirelli, Goodyear) offer longer life and better wet performance.

WoF and Tyres

Tyre condition is inspected at every WoF. Inspectors check:

• Tread depth (minimum 1.5 mm)
• Sidewall damage — cuts, bulges, exposed cords
• Correct tyre size for the vehicle
• No mixing of radial and cross-ply tyres on the same axle

A tyre failure at the WoF means the vehicle cannot be driven until the tyre is replaced.

Further Reading

• Find a mechanic near you
• Wheels and Rims: Alloy vs Steel and What Bent Rims Mean for Safety
• TPMS: What the Tyre Pressure Warning Light Means
• Wheel Alignment: What It Is and Why It Matters