Are your tyres safe and legal?

March 8, 2017

Checking Legal Tyre Tread Depth

Are your tyres safe and legal?

Checking the depth of your tyre tread is one of the most important inspections you can make on your car. The rubber around the circumference of a tyre is referred to as the tyres tread. A new car tyre begins with approximately 8mm of tread.

The more you drive the more contact the tyres have with the road which causes the tread to gradually deteriorate.

Once this happens, the tyres grip loses its effectiveness which can increase the risk of an accident. Not only that but if all 4 tyres are worn below the legal limit, you could potentially lose your licence and face a £10,000 fine.


Do you know what the pattern on your tyre does?

The pattern moulded into the rubber is called the grooves. The grooves do not make contact with the road whereas the tread does.

tyre tread

Water acts as a lubricant when braking so the purpose of the grooves is to allow the water to be released from below the tyre to avoid the tyre to skid and swerve.

The grooves are designed to eradicate excess water but if excessively worn, the stopping distance dramatically increases because the tyres cannot provide the traction they need in order to stop.

In heavy rain, each tyre can shift one gallon of water per second, therefore a deeper tread means the tyres can work to their potential, improving the traction and grip.

That is why tyres that are intended for summer and dry weather are designed with minimal patterns.

When should you get your tyres checked?

The minimum legal tread depth is 1.6mm, however most motoring organisations recommend changing at 2mm and the majority of tyre manufacturers recommend changing them at 3mm.

stopping distancedepth indicator

Tyres may also include Tread Wear Indicators (TWI) these indicators are small raised bridges within the grooves. When the tread is worn down to the point that the limit indicators make contact with the road, it means that the tyre tread depth is approaching the illegal limit of 1.6mm. This means it has come to the end of its service life. At this point you should have your tyres checked and replaced.

 Tread Wear Indicators (TWI)

There are a number of factors that can affect the wear of your tyres for example; you’re driving style, the weather, pot holes and road surfaces.

The stopping distance on a worn out tyre

For example, if you brake at 70mph on tyres with 1.6mm tread, you will still be travelling at a speed of around 50mph when the same car with a 3mm tread will have stopped, adding up to 3 bus lenghts to your stopping distance. This increases the risk of an accident and can put others on the road in danger.

Research shows that tyres with 3mm tread had a 25% better performance than those at 1.6mm — which represents an extra 8 metres in wet conditions.

Stopping Distance Chart

The 20p test

The 20p test is a very quick and easy way to check the tyre tread and depth.

  1. Take a 20p coin and insert it into the tread grooves on the tyre.
  2. If you can’t see the outer band on the coin, your tyres are above the legal limit.

We suggest drivers should conduct the 20p test once a month.

20p Tyre Test

The Legal Requirements

    • For tyre tread below the minimum limit of 1.6mm, the driver will receive 3 penatly points and a £2,500 fine per tyre.
    • If involved in an accident with illegal tyres which are below the minimum limit, the insurance claim could become invalid.

The cost of new tyres can be an expensive investment but definitely worth it in comparison to a £10,000 fine.

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