Tyre Size Comparison Calculator

Tyre sizes in New Zealand use the same international format as most of the world. A typical tyre size code such as 205/55R16 91V breaks down as follows: 205 is the tyre section width in millimetres; 55 is the aspect ratio (the sidewall height as a percentage of the section width, so 55% of 205 mm = 112.75 mm); R indicates radial construction (the most common type); 16 is the rim diameter in inches; 91 is the load index (each number corresponds to a maximum load capacity, with 91 indicating a maximum load of 615 kg per tyre); and V is the speed rating (indicating the maximum speed the tyre is rated for, with V indicating 240 km/h). The load index and speed rating are critical safety specifications. These codes are moulded into the tyre sidewall. Additional markings may include the DOT date code showing the week and year of manufacture. Source: NZTA (nzta.govt.nz/vehicles/vehicle-safety); Tyre and Rim Association of NZ.

In New Zealand, your replacement tyres must meet or exceed the load index and speed rating specified for your vehicle. The minimum requirement is to match the original equipment manufacturer (OEM) specification listed on your vehicle's tyre placard (usually found on the driver's door jamb or in the owner's manual). The load index must be equal to or higher than the original spec to ensure the tyre can safely carry the vehicle's weight. The speed rating must be equal to or higher than the vehicle's maximum design speed. For example, if your vehicle's placard specifies a load index of 88 and speed rating H (210 km/h), you should not fit tyres with a lower load index or a speed rating below H. Fitting underspecified tyres can result in tyre failure, loss of control, and a failed WoF inspection. Your tyre retailer can confirm the correct specification for your vehicle. Source: NZTA (nzta.govt.nz/vehicles/vehicle-safety); Tyre and Rim Association of NZ.

In New Zealand, fitting a different tyre size to your vehicle is permitted within certain limits. A common practice is "plus-sizing", where a wider tyre with a lower sidewall profile is fitted on a larger rim, while maintaining approximately the same overall tyre diameter to preserve speedometer accuracy. For example, replacing a 195/65R15 with a 205/55R16 maintains a similar rolling circumference. The key rule is that tyres must not foul (rub against) the wheel arches, suspension components, or body at any point, including on full lock and with suspension travel. NZTA requires that tyre fitment does not create a safety hazard. A vehicle will fail its WoF inspection if tyres are incorrectly fitted. It is strongly recommended to consult a qualified tyre specialist before fitting non-standard sizes. Spacers that push tyres beyond the body line may also create compliance issues. Source: NZTA (nzta.govt.nz/vehicles/vehicle-safety); Tyre and Rim Association of NZ.

In New Zealand, the legal minimum tyre tread depth is 1.5 mm across the central three-quarters of the tread width around the full circumference of the tyre. This standard is set by the Land Transport Rule: Tyres 2001. Most new tyres start with approximately 7 to 8 mm of tread depth. While the legal minimum is 1.5 mm, most tyre and safety experts recommend replacing tyres at 2 to 3 mm, as wet-weather braking and handling performance deteriorate significantly below 3 mm. Tyres have tread wear indicators (TWI) moulded into the base of the main tread grooves at approximately 1.6 mm depth; when the tread surface is flush with these indicators, the tyre is at or below the legal minimum. A tyre with insufficient tread depth will fail a WoF inspection. Driving on bald or near-bald tyres significantly increases the risk of aquaplaning and loss of control in wet conditions. Source: NZTA (nzta.govt.nz/vehicles/vehicle-safety); Tyre and Rim Association of NZ.