Media statement | 7 August 2007

Tests confirm risks of mixing tyres

Land Transport NZ is reminding motorists of the potential risks of driving vehicles fitted with inappropriate tyres, including the mixing of winter tyres and summer tyres on the same vehicle.

The warning follows tests conducted in Australia on behalf of the New Zealand Police to assist with the investigation of a fatal loss of control crash near Levin in January this year. The crash involved a vehicle fitted with traditional summer tyres on the front axle and specialist winter (snow) tyres on the rear.  

The tests established that in wet conditions, the mixing of aged worn snow tyres and new summer tyres on the same vehicle can result in loss of control when the vehicle is subjected to a sharp steering input.

The tests also confirmed that the fitting of four tyres of the same type and make all the way around the vehicle – whether they are traditional summer tyres or snow tyres – generally provides better grip than a mixture of tyre types. The best grip (in normal conditions) is provided by the fitting of four summer tyres.

“Having the right tyres in good condition on your vehicle will help you maintain control when conditions change, and give you the best chance of stopping safely or steering your way out of trouble in an emergency,” said Land Transport NZ Vehicles Manager Don Hutchinson.

“Tyres must be properly inflated and have adequate tread depth to perform their best, but they should also be fitted in the right combination. We strongly recommend against mixing snow tyres and summer tyres on the same vehicle, as doing so can seriously compromise your ability to control the vehicle in an emergency. If you have any doubts about the safety or suitability of the tyres on your vehicle, we urge you to check with your local tyre retailer as soon as possible. Many offer free checks and advice.”

Snow tyres are made with a softer rubber compound and deeper treads specifically designed to maintain grip in cold weather (below 7C), ice and snow. They can be distinguished by their deep square-patterned tread blocks. Newer snow tyres are also marked with a ‘mountain snowflake’ symbol on the sidewall.

Specialised snow tyres should not be confused with the broader category of all-season ‘mud and snow’ tyres (often marked with the letters ‘M+S’ on the sidewall) which are designed to perform safely in a wide range of summer and winter conditions, and are commonly fitted to 4WD vehicles. 

“The vast majority of New Zealand motorists have no need for specialised snow tyres on their vehicles at any time of year. For a very small number of drivers – those regularly driving in ice, snow and cold temperatures – snow tyres may be appropriate. In these cases the snow tyres should be fitted in sets of four, and changed at the end of winter,” Mr Hutchinson said.

• Snow tyres - questions and answers

For more information:

Andy Knackstedt
Media Manager
Land Transport NZ
(04) 931-8829 or 0212 763 222