Checking your tyre treads

How to Measure Tyre Tread Depth

There are three ways you can measure your tyre tread depth:

  1. 20p Test: the simplest and most widely known test is to take a 20p coin and check whether the outer band is visible when inserted into the grooves on your tyre. If you can see the outer band of the coin, your tyres will need to be replaced.
  2. Tread Depth Gauge: you can purchase a tread depth gauge quite cheaply and use it to measure your tyre tread. They’re also small enough to fit in your glove compartment, so they’ll always be there to check every few weeks.
  3. Tread Wear Bars: Look for the TWI (Tread Wear Indicators) sidewall markings on your tyre, which will line up with the tread wear bars in the grooves of your tyre. If the bars are smooth with your tyre tread, it’s time to invest in new tyres.


checking your tyre

Things to look out for:

When you’re checking tyre tread depth, you should also be on the lookout for other signs of damage:

  • Something’s lodged in the tread: Small stones or other bits of debris can get stuck in your tyre tread regularly. Most of the time these items are easy to remove. However, occasionally you may find something like a nail or screw that looks as though it’s gone through the rubber. It’s best to take your car to a garage, rather than remove it yourself as you may end up with a flat tyre.
  • Tyre wear on the outside: Tyre wear on the outside edges of your tyre is a sign that your tyres are underinflated. Tyre pressure will decrease over time when used regularly but driving on underinflated tyres uses more fuel and puts you at greater risk of accidents, so keeping your tyres inflated to the correct pressure is important. If you notice that only the front tyres have worn edges, you might be taking corners too quickly. 
  • Visible tread wear bars: You can only see these bars of hard rubber when your tyre’s tread has become worn. If you can see them, your tyres need replacing. If you’re not sure where they are, you’ll see a mark on the sidewall that indicates where to look.
  • Your tread is less than 1.6mm: Under European law, your treads must be at least 1.6mm deep around the tyre’s circumference. For winter tyres, Dunlop recommends a minimum tread depth of 4mm. Check them with a tread depth gauge (they aren’t expensive if you haven’t got one) and make sure you measure both the inside and outside of your treads.
  • Tyre wear in the centre: When your tyres are wearing more in the centre of the tyre, you may have overinflated tyres. If your tyres are overinflated, this will increase the risk of rapid deflation. Check your tyre pressure and deflate it to the recommended pressure.
  • Uneven wear across a single tyre: The wear patterns on your treads might indicate problems elsewhere. If you notice uneven patches of wear, or bald spots, you might need your wheels balanced or aligned. Sometimes bald spots indicate that your shocks are worn.
  • Uneven wear: If you notice uneven wear or bald spots on one of your tyres, or on one particular side of your car, you might need to get your wheels balanced or aligned. Sometimes bald sports can also indicate that your shock absorbers are worn. If you can see uneven wear on your front tyres, you may need to get your suspension checked. 
  • Sawtoothed pattern: If your tyres have a sawtoothed or feathered appearance around the edges, you may need to have your wheels aligned as it is likely that the tyre is rubbing erratically against the road. A useful test is to run your hand around the tread in both directions. If it is smooth one way and rough the other, this is sawtoothing.

What’s the Legal Limit?

The legal limit for tyre tread in the UK is 1.6mm but it’s important to look after your tyres and check the tread often. For winter tyres, you should change your tyres when your tyre tread reaches 4mm. 

How Much Tread on a New Tyre

A brand new set of tyres will have approximately of 8mm tread depth. So it goes without saying how much impact on grip, traction and braking distance there will be when this tread depth is reduced to 1.6mm.

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