Tires talk to us through their uneven wear, did you know that?

Summer is here and it’s time to hit the road with our car, the family, the luggage and, of course, the beach toys. We should always keep our car in good condition, but it’s true that we worry more when planning a trip of several hundred kilometres.

If it has been several months since we had our car serviced, it is advisable to take it back to a workshop so that the experts can take a look and check that it is ready for that family trip. If the service was done recently, we should not take it “lightly” either: we ourselves should check at least the most basic items, such as the levels of the various fluids (oil, antifreeze, windscreen washer fluid, etc.), the tyre pressures, without forgetting the spare wheel, and the visual condition of the tyres.

Today we are going to focus precisely on the latter, on what a tyre tells us at a glance. But we are going to go further than how close the “wear indicator” is to the maximum permitted wear, by checking and helping you understand the different uneven wear patterns that can appear. I think there is no need to remind you that tyres, together with the braking system, are the most important part of a car.

Naturally, the ideal is for a tyre to wear evenly across the whole tread. That is, the tread, which is the part in contact with the asphalt, should wear uniformly, without premature wear on one side, on both sides, or in the centre of the contact surface.

However, this is not always the case, and we may find that our tyre is closer to the wear indicator (the “tell-tale”) in one area than in another. In the vast majority of cases this is due to a problem with the alignment, more commonly known as “toe”, or to incorrect tyre pressure; although it could also be caused by a defective rubber compound or by very demanding driving on tyres that are not suitable for sporty driving.

Wear due to incorrect tyre pressure

I’m sure most of you, dear readers, know how high or low air pressure affects a tyre, but let’s review it quickly.

• If they wear more quickly on the outer edges, it means the pressure is lower than it should be. With less air than it should have, the tyre “flattens” and does not make contact as it should, also touching the shoulders of the tyre on the road. In addition, this contributes to higher fuel consumption and possible overheating of the rubber, which will lead to even greater wear.
• Conversely, if the premature wear appears in the centre of the tread, it means that wheel is over-inflated. Being more inflated, the central area expands and, therefore, the edges of the tread make much less contact with the ground, so the central part wears. In this way we lose grip.

We must not forget that, when we go on holiday, we usually travel with several people in the car and a loaded boot, so the total weight increases considerably. On the car itself we usually have the pressure data, which are shown for light load, normal load and heavy load. Remember it.

Uneven wear due to steering geometry

Uneven wear is not caused only by incorrect pressure inside the tyre. It can also appear due to other factors, mainly the steering geometry.

In this case, the wear will in most cases affect both wheels on the same axle equally. That is, if the right wheel wears more on its right side, the left one will do so on its left side (outer edges of the tread).

We do not want to explain in depth the steering geometry and the various angles that affect a car’s alignment, since that would require a separate article, which we will leave for another day. So we will explain it simply and without too many complications.

• Greater wear on the outer side: This can be due to very sporty driving, but let’s set that aside and focus on anomalies arising from normal, everyday driving. A tyre showing less tread on the outer side is usually caused by excessive toe-in. To give you an idea, the wheels always point “slightly” inwards, as if they wanted to cross a few metres ahead of the car. This is called “toe-in”, and if it is excessive it causes that outer wear.
• Greater wear on the inner side: We must pay attention and check, as we should, the inner side of the tyre. Since it is not easily seen with the wheels straight, we may notice this problem too late. To check it, we just need to turn the wheels fully and take a look. The greater wear on the inside of the tyre is also caused by toe, but in this case negative toe, when the wheels, instead of “wanting to meet” a few metres ahead of the car, try to separate. This is known as negative toe-in or toe-out.

This inner wear can also be caused by an incorrect camber setting. Just as the wheels are normally pointed inwards in toe-in, they have a slight inclination on the imaginary horizontal axis that tilts them slightly towards the centre of the engine bay (on the front axle), so they rest a little more on the asphalt on the inside of the tyre. On road cars it is barely noticeable, but it can be seen with the naked eye on competition vehicles.

Braking without ABS?

Finally, although it is not common to see it nowadays, we have the famous flat spots. This defect appeared after a hard braking with the tyres locked, and was even more noticeable when the asphalt temperature was high, that is, in summer. Nowadays, and for several years now, all vehicles approved for circulation on public roads in Spain must be fitted with an anti-lock braking system, the well-known ABS, which prevents the wheels from “squaring off” during an emergency stop.