1. Cars home
  2. Motoring Rules & Regulations

Ask an expert

mattgtalbot
By mattgtalbot | AA Member | 2 Posts | 10 February 2014 at 9:48am

Hi , Does the AA have a guideline for tyre replacement in regards to tread level ? . i have a heavy work company vehicle that does 800km per week , ive had mixed messages from friends , workshops and tyre shops as to the required safe replacement tread level. i know the legal limit is 1.5 mm and my fleet manager will only replace at this measurement contrary to advise from tyre shop manager

ABayliss
By ABayliss | AA Expert | 2169 Posts | 10 February 2014 at 10:56am

As you say, from a legal standpoint, tyres are road legal with a minimum of 1.5mm of tread depth. Most tyre manufacturers have wear bars in the tread of the tyre, so if the tread is worn down to the wear bar, the tyre is at its minimum legal depth.
However, under some road conditions (particularly wet conditions), a tyre worn down to the legal minimum will not perform as well as a new tyre. It stands to reason that a new tyre with say 8mm of tread will be at its optimum level in terms of dispersing water, and the lower the tread becomes, the amount of water a tyre can disperse will reduce. That said, manufacturers carry out extensive testing and believe that tyres will continue to provide adequate performance down to their minimum (wear bar) level.
As a recommendation, we suggest people start thinking about tyre replacement when the tyres get down to about 2mm, but there is no legal obligation to do so.

mattgtalbot
By mattgtalbot | AA Member | 2 Posts | 10 February 2014 at 8:01pm

Thanks for your reply Andrew .
Would i be correct in telling my manager that the tread limit is like the road speed limit and should not be used as a target or used to over rule good professional advice or good judgement ?

ABayliss
By ABayliss | AA Expert | 2169 Posts | 11 February 2014 at 8:55am

I can understand your concern but regardless of any argument you present your fleet manager is under no obligation to replace the tyres if they still meet legal requirements.

p.dath
By p.dath | AA Member | 3 Posts | 3 July 2016 at 8:50am

I like to replace tyres when the tread depth gets down to 3mm. 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.