What is the legal tyre tread depth and how to check it
There’s an old adage that states “a stitch in time saves nine.” It generally suggests that tending to small problems before they get worse prevents further work later on.
Tyres are the only parts of a vehicle that make contact with the road surface, so it’s imperative that they are at the forefront of your mind every time you sit in the driver’s seat. Ignore them for too long and you could receive a hefty fine of up to £2,500 – or worse, put you and your passengers’ safety at risk.
In this post, we discuss how to check tyre tread depth, what the legal limit is, and what causes uneven tyre wear.
Why is tyre tread depth important?
A tyre tread makes up the little grooves and ridges that run along the circumference of a tyre’s rubber surface. These might not look like much, but they’re absolutely essential.
Each one of these grooves offers grip to the road surface, allowing you to brake and manoeuvre safely. As tread depth decreases, a tyre’s performance deteriorates, making it difficult to transmit traction to the road effectively. Allow your tyres to become over-worn and you run the risk of greater stopping distances and less control.
A deep tyre tread will also quickly channel water away from the rubber, so it doesn’t lose contact with the road. This makes tyre tread depth essential when roads become wet and hazardous, as it prevents aquaplaning.
What causes tyre wear?
The tread depth of a new tyre is approximately 8mm, but naturally this becomes shallower over time. Causes of tread deterioration include:
- Type of vehicle
- Driving style/habits
- Quality of tyre
- Overloading
- Improper inflation pressure
- Improper tyre alignment
While the typical lifespan of a tyre will differ depending on the above factors, it’s generally considered prudent to order a replacement once the depth reaches 3mm (RoSPA found that this is the point at which stopping distances start to increase dramatically). Similar research suggests over or under inflating a tyre reduces the traction between the rubber and road, which leads to increased tread wear and greater stopping distances.
“If your vehicle starts to lose road grip or doesn’t handle correctly in adverse weather conditions, you should consult a tyre specialist ASAP.”
UK tyre law: what is the legal tyre tread depth
UK law stipulates that a car should have a minimum tread depth of 1.6mm in a continuous band around the central three-quarters of the tyre. The same rule applies to goods vehicles, such as vans, trailers and caravans that don’t exceed 3500kg.
If you are caught driving with defective or “bald” tyres, it could result in:
- A fine up to £2,500 per tyre
- Three points on your licence per tyre
- An insurance claim made as a result of an accident becoming invalid
It is also illegal to use a tyre that:
- Has any portion of the ply or cord exposed
- Has a bulge or tear
- Is not correctly inflated
- Is not maintained in a fit condition
- Is unsuitable in regards to the vehicle’s use
While UK tyre law states that a wheel should have a minimum tread depth of 1.6mm, most motoring experts would recommend replacing a tyre once the tread gets to 2-3mm. This is confirmed by RoSPA’s study, which found stopping distances increase by 44.6% on smooth concrete at the legal minimum tread depth.
How do I check tyre tread depth?
The most accurate way of checking your tyre’s tread is with a purpose-made tool called a tyre tread depth gauge. This is what the technicians at Tyres On The Drive use to quickly and accurately measure the depth of an individual tyre groove. Many of these handy gadgets also allow you to check car tyre pressure. If you have one to hand, simply insert the probe bar into the groove and then push the shoulders flush with the tread.
If you don’t have a tyre tread depth gauge, you could check the tyre’s tread wear indicators (TWI), or wear bars. These are evenly spaced through the main grooves in the tyre tread and allow you to take a visual reading. In some instances, a small triangle marking will denote the position of the tread wear indicator. If the indicator is flush with the level of the tread, then the tyre should be replaced.
The 20p test
You will often hear people refer to ‘the 20p test.’ This is the quickest and easiest way to check your tyre’s tread depth – but also the least accurate.
How to perform the 20p test:
- Place a 20p coin into the main tread grooves of your tyre.
- If you can’t see the raised edge around the coin, your tyre’s tread is likely greater than 1.6mm and, therefore, legal.
- If, on the other hand, the outer band is visible when inserted, your tyre could be unsafe and require professional inspection.
- Cornering and alignment can cause the tread across the tyre to wear at different rates, so remember to also take multiple measurements across the central three-quarters of the tyre.
How often do I need to check my tyre tread?
Living in the UK means having to contend with adverse weather conditions on a regular basis, so it’s best to check your tyres frequently to make sure they’re fit for use. But how often is frequently? Here’s what Daniel Bezer, tyre expert at TOTD, recommends:
“Carrying out basic but essential tyre checks can mitigate many potential issues drivers might suffer. This could include anything from preventing delays and additional expense to dangerous cases of injury. At TOTD, we recommend checking your tyres once every couple of weeks and especially before long journeys to minimise the risk of tyre-related incidents.”
Still unsure whether your tyres are fit for purpose? Need advice on tyre tread depth? Get in touch with our customer support team by calling 0333 016 6550, or find the perfect replacements simply by typing in your registration details.
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