The MTA’s (Motor Trade Association) latest road safety initiative is this leaflet discussing the importance of having sufficient tread on all 4 tyres, how wet weather braking is impaired by low tyre tread depth and how much of a tyre is in contact with the road in 1 mm of water. While the footprint and road contact of a new tyre with 8 mm of tread remains almost the same up to 90 kph, 50% worn tyres with 4 mm of tread have greatly less road contact at 90 kph. Heavily worn tyres at the legal limit of 1.5 mm have even less.
A tyre with 1.5 mm of tread takes twice the stopping distance of a new tyre in the wet.
Obviously tread depth is crucial to motoring safety; the MTA recommends that tyres with tread lower than 2 mm are replaced immediately and those with 2 to 4 mm are replaced soon, Tyres with tread ranging from 4 to 13 mm are regarded as being in good condition.
The Campaign for Better Tyres is encouraging motorists to regard 4 mm of tread as the minimum safe tread depth; this will require a big change in the thinking of Kiwi drivers but would pay a big dividend in terms of road safety. Certainly, the current 1.5 mm minimum legal tread depth is not sufficient for safe driving on wet roads.