Understanding tyre tread depth essentials, and how to check that yours are safe and legal

Understanding tyre tread depth essentials, and how to check that yours are safe and legal

31 Jul

By Gwyn Fennell

Some can appear trivial, while others are more serious. And when it comes to statistics, British motorists are as inundated as everyone else, and the numbers are usually important.

The most complete annual figures – from 2016 – show that there were a staggering 37.1 million vehicles licensed for use on UK roads, with 1.87 billion car miles driven, and just under 180,000 road casualties. Of these, a startling 1,792 were fatalities – the highest level since 2011.

It can be difficult to comprehend such large figures, so consider this small number: 1.6 mm – the minimum tread depth your tyres must have to be UK road legal. 1.6 mm doesn’t sound a lot, but it’s the difference between having (legally acceptable) tyre grip, and becoming one those road casualties.



If yo think we’re being dramatic, consider this: The area of a tyre that is in contact with the road at any given time is roughly the size of your smartphone. That’s it! And with this limited contact, tyres are required to remove sufficient water from the road so as to provide you with the essential grip you require to stay in control – and safe.

To acheive this, tyres require sufficient tread depth, otherwise they can’t remove water quickly enough to generate grip. Unfortunately, many British motorists don’t realise this, and, as a result, allow their tyres to wear down – to a point where they no longer have sufficient tread depth.


Your tread depth helps to determine your breaking distances – and protects against the threat of aquaplaning

While it’s true that just 1.6 mm is the UK road legal minimum tyre tread depth, the vast majority of road safety organisations and tyre experts – including Protyre, and premium tyre manufacturer, Continental – strongly recommend – and actively campaign for – an increase to the minimum tread depth of 3 mm.

It doesn’t sound like much of an increase, but independent braking distance tests conclusively reveal that in wet weather conditions, the difference in breaking distance for 1.6 mm and 3 mm tread depths is almost twice as far to come to a safe, full stop.

The graphic, above, demonstrates the difference in stopping distances for vehicles fitted with summer tyres on a wet road. Even at relatively modest speeds (21 mph residual speed for the 3 mm tread, and 27 mph residual speed for the 1.6 mm tread) the difference is alarming. In a built up, urban environment – such as where school children are distracted while crossing the road, for instance – the consequences of requiring a much longer stopping distance are terrifying. And as for travelling at high speed on a motorway… it really doesn’t bear thinking about, does it?

And then there’s the devastating threat of aquaplaning – when your tyres completely lose contact with the road, and as a result travel on top of the water – out of control. When you aquaplane, tyres are resistant to all efforts to accelerate, brake or steer, leaving drivers out of control. Fortunately – in the main – drivers usually get control back, but this is not always the case, and can lead to accidents – and fatalities.


How you drive will speed up or slow down tyre tread wear

When a premium tyre leaves the factory – such as the award winning ContiPremiumContact™ 5 – it features 8 mm of tyre tread depth. This allows the tyre to remove large amounts of water quickly and efficiently from the road, significantly improving grip, vehicle handling, driver comfort, and – most importantly – safety. But while all tyres tend to look similar, in fact they’re not all the same. Far from it.

A tyre’s compound – the material it’s made from – in combination with how a car is driven, will determine a tyre’s tread depth wear. Driving thousands of miles a year at 70 mph on motorways will see tyres deteriorate faster than, for instance, doing a short school run five days a week. But in an exact like for like usage comparison, the superior compounds used for premium tyres will wear down much more slowly than those used to make cheaper, budget tyres.

This means you’re likely to have to change your tyres more often, if you fit budgets instead of premium tyres. However, ultimately, no matter how you drive, all tyres will eventually wear down. For this reason, it’s vital that you regularly check your tread depth.


Checking your tyre tread depth couldn’t be simpler

While tyre tread depth gauges are available to purchase, an alternative to this is the “20p Test”. It’s an incredibly easy way to check your tread depths, and so simple to do. Just place a 20p coin into the tread grooves that run along the length of your tyre. Do this at various points, so that you have a broad set of results.
If the coin’s outer band is totally obscured, you know for sure that your tread is above the legal minimum (at the points you checked). But if you can still see the top of the band – at any point that you test – your tyres may be illegal. In this situation you need to seek immediate expert advice from your local Protyre garage, and if necessary replace your tyres.

If you don’t, and you’re stopped by the police with illegal tyres fitted, you run the risk of getting a fine of £2,500, and three penalty points for each illegal tyre. And don’t forget, without enough tread depth to generate the grip you need, you’re not only endangering yourself, but also your passengers and other road users.
 

If you’re unsure about tyre tread depths, speak to the experts at Protyre

Your tyre tread depths are very, very important. If you’re unsure about yours, or how to checkthem, speak to your local Protyre professionals for impartial, expert tyre advice and fitting solutions.

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Author

Gwyn Fennell
Gwyn has been in the motor industry for over 35 years with experience in vehicle design, electrics, engine management, geometry and of course tyres. Continental has been Gwyn’s home for the past 15 years, where he has become a qualified trainer and examiner to both IMI and NTDA standards and now working towards the IQA qualification. Gwyn’s job has evolved and expanded in recent times and a more accurate but less pleasing to read title would be Technical Customer Service & ContiAcademy Training Centre Manager. It’s no surprise that Gwyn has excellent knowledge from the tyres up so when any technical questions come his way you know he’ll be providing the best advice possible.
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