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Tyre Depth And Why You Should Change At 3mm

March 8, 2019

At present the law states that you should have a minimum of 1.6mm of tread depth on your tyres. The only problem with 1.6mm is that after 3mm the stopping distance for a car will greatly increase, at 1.6mm the stopping distance can be up to 44 meters longer (about 10 car lengths) than a similar car with a 3mm of tread left, that 44 meters (or 144 feet and a bit if you use old money) could be the difference between having and accident and avoiding one.

A survey of 100 random cars found that 67 cars had at least 1 tyre below the recommended 3mm limit. Now having to change your tyres at 3mm instead of 1.6mm will cost you more, how much I hear you say. Well about £20 a year, now divide that by 52 weeks and it comes to just under 39p a week. Not a lot really and if you take into account your insurance excess if you do have an accident that you could have avoided then 39p a week could be seen as a bit of a bargain.

It could be said that the minimum depth should be even higher. The more tread in contact with the road the better, but a study by MIRA in 2003 showed that 3mm was the critical depth at which the level of grip quickly reduces as the tread depth reduces.

Most drivers don’t realise how important the tread depth on their tyres are. It is not until you are skidding towards a car in front of you that you really appreciate what your tyres are doing for you and how they can keep you safe, but as we all know it is too late at this point.

Braking distances are not the only thing that is affected by tread depth. The risk of Aquaplaning is greatly increased at 1.6mm as against 3mm; the reason for this is that the reduced tread cannot remove the water as efficiently.

Lots of car manufacturers also recommend that tyres should be changed at 3mm. Look at your handbook to see what they have to say about the recommended depth that tyres should be changed.

So why are we stuck at 1.6mm, it all goes back to 1992 when cars had skinnier tyres, the tread depth law before 1992 was 1mm. Since then tyres have got wider, this means that you have a larger contact patch with the road. Great when it is dry as more contact equals more grip, but when it is wet wider tyres take less water pressure to lift up the car and thus you get Aquaplaning (think of it as a thin tyre cutting through the water and a wider tyre sitting on top of it, a bit like an airboat in Florida with its flat wide bottom that skips over the top of the water and a speedboat that cuts through the water)

So why don’t they just change the law, not that simple, the 1.6mm minimum tread depth for car tyres is set across the EU by a European directive, and at the moment there are no plans to change this. So are the Europeans happy with the 1.6mm, not all of them. The TUV (the German equivalent to our Transport Research Lab of TRL for short) would like to increase the limit to at least 2.5mm. The German motorist is generally a more cautious and understands the dangers and changes their tyres before they get to 1.6mm, one of the downsides of this is that the old tyres are then shipped to the UK to be sold as part worn tyres with all the inherent problems you get with second-hand tyres.

Your car will take an extra 11 car lengths further to stop in wet conditions at 50mph when your tyres are at 1.6mm.

So until the eurocrats decide that the rules need to be changed we will be stuck with a legal minimum of 1.6mm and a recommendation of 3mm, is it really worth taking the risk for just 39p ??

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