Ask an expert
The tyre tread on my car are all down to 3mm. I gather that the legal limit is 1.5mm which seems very low to me.
At what point would you recommend changing the tyres?
Kenvyn
From the "Ask Jack" archives - 23 April 2010
Less than 1.5mm tyre tread is considered to be unsafe (illegal) and the end of the useful life of a tyre.
A new car tyre in comparison has approx 7-8mm of tread.
Obviously as any tyre starts to head towards the minimum tread depth some benefits are lost in comparison to a new tyre. In-cabin road noise levels is one such characteristic I recently discovered as the tyres on my car headed toward the 1.5 mm limit. New tyres have certainly made the driving experience much more pleasurable.
If tyre pressures are maintained and the tyres are in good all-round condition I would have no safety issues driving with a tread depth just above the legal limit.
Where things can get tricky is when a tyre tread depth becomes marginal at Warrant of Fitness time. Inspectors must pass a tyre on tread depth and general condition at the time of inspection, so in theory a tyre can pass an inspection with a tread depth of only 1.5mm.
Normally a warning is given when tyres reach a marginal limit but if this is ignored it doesn't take long for a tyre to be below the legal limit. In this condition the car becomes very unsafe to both the occupants and other road users.
The other important point to remember with tread depth is the tyres ability to disperse water on wet roads.
I would certainly be keeping a close eye on the tyres and take action a little early rather than wait until the last minute especially as we head into winter. Obviously the amount of driving you do will determine the tyre life you have remaining.
If you can, replace your tyres at 3mm of tread depth. The legal minimum in NZ and Australia is 1.5mm. In the UK it is 1.6mm.
There is a substantial drop in wet breaking performance under 3mm of tread depth. Some studies have shown that going from 3mm to 1.5mm results in a 25% reduction in wet weather braking performance. 25% is a lot - it equates to a good 2 car lengths.