When driving, it is vital to have car tyres that are safe and of a decent quality. One of the key factors of this is the level of tread wear that your products have gone through. Checking your tyres for this can highlight when they are in need of replacing or repairing.

It is also vital for recognising when your tyres are completely worn down and must be replaced. In short, a worn tyre can be defined as:

  • A tyre with a tread depth that has reached the tread wear index - 1.6 mm - marked in several places around the circumference.
  • A tyre with damage that makes it impossible to use.
  • A tyre so old that it is no longer safe or usable.

Similarly, tread wear comes in many different forms, many of which mark a tyre as unusable. These include:

  • A tread shallower than 1.6 mm, the UK legal minimum.
  • Split tyre elements, such as a separated tread.
  • Deformed or exposed bead wire (the element that holds the tyre onto the car wheel).
  • Stains or other discolourations on the butyl layer, similar to a visible marble pattern.
  • Bulges or deformations of the sidewall, caused by broken threads in the tyre carcass.
  • Any cuts or tears in the sidewall, even if superficial, that damage the carcass.

If you notice any of these symptoms, you should consult a professional tyre shop to see if it can be repaired or if you need new car tyres.

Here, however, we will go into the various forms of tyre tread wear patterns more closely, so you can identify the condition of your tyres more easily.

Tread depth and tyre traction

A tyre with a minimal tread depth performs far worse than a tyre with new treads, especially when wet handling and resistance to aquaplaning are concerned. A tyre with a 4 mm tread has only 65% of the grip that an 8 mm tread would have on a wet surface. Compared to a new tyre, a tread at the legal minimum (1.6 mm) only has 40% of the wet grip available.

tread-wear-1-01

Tread wear - the TWI symbol shows the tyre is worn down to 1.6 mm.

So, with this in mind, what are the different types of tread wear and how can you recognise them? In short, we can list the following types of tread wear:

  • Normal wear
  • Asymmetrical wear
  • Round wear (shoulders)
  • Wearing along the middle (concave)
  • Spot wear
  • Feathering

tread-wear-2-02

Tread wear bulges in the sidewall. Photo: Michelin.

Normal wear refers to situations where the tyre is worn evenly across the whole width of the tyre, as well as along the whole tread. This is normal, as all tyres become worn through use.
 
Asymmetrical wear is the result of one side of the tread wearing faster than the other. This can be the result of an incorrect car toe or camber, causing the tyre to be at an irregular angle to the road.
 
Shoulder wear, also known as rounding, means that the edges of the tread are higher than the middle.
 
Wearing along the middle of the tread, also known as concave wear, is caused by over inflating the tyres. This incorrect tyre pressure causes the contact patch to be limited to the middle of the tyre, which is bulging, causing this section to wear much faster.
 
Spot wear is often caused by sudden braking with locked wheels, which can occur in cars without ABS. This causes intense wear in one part of the tyre, as the locked wheels mean the tyre cannot rotate. Similarly, it can also be caused by the use of a low quality rubber compound in the tyre construction.

tread-wear-3-02

Tread wear: two typical tread wear patterns caused by improper inflation.

Middle wear – probably caused by prolonged driving with overinflated tyres or an aggressive driving style.

Side wear – probably caused by prolonged driving with underinflated tyres and aggressive cornering.

tread-wear-4-02

Tread wear: two tread wear patterns caused by the car’s suspension or incorrect balancing.

One-sided wear – probably caused by incorrect toe or problems with the car suspension system.

Spot wear – probably caused by sudden braking, incorrect balancing or alignment.

Feathering is also a frequent tread wear pattern found on many tyres, indicating that the tread blocks have been worn down unevenly. This results in a saw-tooth pattern that is both visible to the naked eye and can be easily felt with your hand.

Ultimately, this effect is inevitable, but it can vary in its intensity, depending on a number of factors, including:

  • Mismatched tyres and car suspension
  • Incorrect tyre pressure and loads
  • Mismatched speed index and load index for a given car
  • Conditions with the suspension

Heavily feathered tyres may be bothersome due to their vibration levels and, consequently, high tyre noise. In order to keep this problem to a minimal, acceptable level, you should rotate your car wheels every 6,200 miles, observe the correct pressure, speed index and load index, as well as caring for your suspension.

tread-wear-5-02

A partly used tyre tread with signs of feathering.

When should I return my tyres?

When it comes to various faults, you cannot rule out the possibility that it was the result of a factory fault. If you are sure you have been using your tyres correctly, observing all recommended pressure and load values, as well as having a car in good condition, and yet the tyres still wear down in an unusual way, this may suggest problems with the tyre’s original quality.

Such problems may cause faster wearing and all kinds of spot wearing. In these instances, you may want to take your tyres to an expert to have them inspected.

Tread wear and road safety

When it comes to safety on the road, tread wear causes two specific problems:

  • First and foremost, it influences how the tyre behaves and handles, thanks to altering its parameters. A shallow tread, for instance, creates a bigger risk of losing control of your vehicle. This is especially true on wet roads, as a thinner tread has a greater susceptibility to aquaplaning.
  • Secondly, there is a higher probability of causing tread wear-related incidents. This includes cracks, tread separation and even the tyre falling off of the rim.
tread-wear-6-02

An example of a broken tyre tread.

How to care for your tyres

For the most part, tread wear is largely dependent on what we, as drivers, do. Subsequently, there are numerous factors that can determine how long you can use your tyres for, rather than having to replace them early on due to tread wear or damage.

This includes:

  • Ensuring the correct pressure for the load of the car
  • Observing and keeping under the maximum load tolerances
  • The driving environment, such as city roads, motorways or dirt roads
  • The frequency or corners and hills encountered while driving
  • Your driving style, which may include sudden braking or excessive acceleration
  • Your car and tyre storage conditions, as well as the position of the tyres being stored
  • Driving over obstacles, such as holes and curbs,  at high speeds
  • Controlling the technical condition of your car, such as the wheel alignment, toe and suspension

Furthermore, regularly checking for the correct tyre pressure is also one of the most important factors. The word “correct” is vital here, as the tyres should have the pressure values recommended by the manufacturer for the given conditions.

The pressure should not be too high, or too low, as this can change the shape and strength of the tyre, leading to uneven tyre wear, bulging and other issues described throughout this article. As an example, under inflating by 20% can shorten a tyre’s lifespan by 30%. It also significantly increases your braking distances and fuel consumption.