For many drivers, knowing when to replace their winter tyres is vital. Done right, you can ensure you always have reliable safety, traction and grip in various winter conditions. Yet, many drivers don’t know when to replace their winter tyres.
Here, we’ve compiled some information on the most important factor: tyre tread depth. This is something you can actually check yourself. While you can inspect your tyre on the car wheel, it’s often better to remove it and do a complete inspection for any irregularities as well.
Tyre tread depth
In the UK, as well as Europe, regulations restrict tyre depth to a tread know less than 1.6 mm deep. This is often easy to check, as many tyres come with a tread wear indicator or a tread wear index, often shorted to TWI, which shows when the tyre reaches a tread depth of 1.6 mm.
A tread wear indicator consists of thicker bars in the grooves, found in the centre of the tread. The TWI label, on the other hand, is typically located on the sidewall.
However, one thing to keep in mind throughout this article, and when checking your own tyre wear indicator levels, is that 1.6 mm is the legal minimum, not the recommended depth. We recommend a minimum of 4 mm, as this is vital for maintaining key properties, such as grip and traction.
In some tyres, this is marked with its own tyre wear indicators, such as a snowflake symbol, to show you when a tyre has lost its appropriate depth for winter driving, yet is still above the legal requirements. At this point, it is often best to replace your tyres.
Some winter tyres have a snowflake-shaped indicator, which disappears when the tyre tread depth is below 4 mm.
Why do I have to replace winter tyres when the tread is less than 4 mm deep?
In winter conditions, a deeper car tyre tread is a must, as these tyres have to squeeze the snow in the grooves and dispose of it, cleaning the tread, while driving. If tyre tread wear has made this too shallow, the bits of snow will stick to the tyre and, since the tyre cannot remove these small pockets of material, they will significantly decrease the traction.
Tyre wear indicators.
This belief that winter tyres lose key properties at 4 mm is supported by many organisations. ADAC, specifically, have conducted their own testing and have found that the properties of winter tyres with 4 mm or less have worse properties than those with a new tyre tread depth.
How do I check the tyre tread depth?
If you want to learn how to measure tyre tread depth, there are actually a number of ways you can do. The best method, however, only requires a pen, a match and a calliper.
Step 1: Measure the tyre tread depth by marking a match.
Step 2: Measure the marked section to record the true tread depth.
How to check tyre tread depth with a 20p coin
One of the easier ways to check the car tyre tread depth is with a 20p coin. However, this is often for ensuring whether or not such a tyre is at the 1.6 mm minimum, rather than offering a accurate figure. Still, it is a quick test and important to do, as breaking the law can result in a fine of £2,500 and 3 penalty points.
The 20p test to check tyre tread depth.
Fortunately, the 20p test is simple, Simply place a 20p coin in the main groove of the tread. If the edge (the outer banding) is not visible above the tread, then it is sufficiently deep enough to meet legal road requirements in the UK. If you can still see this edge, then your treads are excessively worn out and should be checked by an expert, or replaced entirely. If you this is the case, you can also use the previous method (using a match) to get a more accurate reading.
An example of a road legal tyre tread depth.
Looking for irregularities
Aside from the tread depth, you should also use this opportunity to check the tyre for any irregularities. These can influence the parameters of the tyres, consequently hurting the safety and performance of your vehicle.
You should inspect your tyres for any:
crosswise cracks in sidewalls or tread, etc.
If you see any of the above, you should visit a professional tyre repair workshop to see how severe the problem is. In most cases, it depends if the damage is on the outside layers, or if it affects the deeper layers of the tyre construction.
An example of a cut tyre.
An example of a well worn tread.