Tyre wear and checks: the answers | Pneumatici SuperStore

Question 1

How do you measure tread depth?

Accepted Answer

It is measured with a depth gauge inserted into the main grooves. Michelin recommends checking at several points around the circumference and across the width of the tyre, on both the inner and outer side. Alternatively you can look at the wear indicators, small raised bars at the bottom of the grooves. If one indicator is reached and the others are not, or if edges and centre give different values, wear is uneven and it is best to have the car checked.

Question 2

What are the TWIs on the tyre sidewall?

Accepted Answer

The TWI (Tread Wear Indicator) is a mark moulded on the sidewall that shows where, at the bottom of the main grooves, small raised bars are distributed along the tread. When the tread wears down to the level of these bars, the tyre has reached its wear limit. On many Michelin tyres the position of the indicators is marked by the Bibendum figure symbol on the sidewall.

Question 3

Why do tyres wear more on the outer edges?

Accepted Answer

When wear affects both shoulders and the centre stays more intact, the typical cause is habitually too low pressure: Michelin and Goodyear state this clearly. If instead mainly one side wears, the most likely cause is alignment out of tolerance (camber or toe) or a suspension problem. It is corrected by restoring the pressure to the manufacturer's value and having the alignment checked by a tyre shop.

Question 4

Why does the centre of the tread wear before the sides?

Accepted Answer

The most frequent cause is habitually too high pressure: the centre of the tread carries more load and wears before the edges, as Goodyear indicates. A smoother central band compared with the shoulders is noticeable. The solution is to restore the pressure to the manufacturer's value, measured cold, and check it regularly. Tread that has already worn cannot be recovered, but correcting the pressure prevents uneven wear from continuing.

Question 5

What does stepped or sawtooth wear mean?

Accepted Answer

It is wear in which the tread ribs are smooth on one side and sharp on the other: running your hand over the tread you feel a sawtooth profile. TyreSafe and Goodyear link it to an alignment defect, in particular toe. It is solved by checking and adjusting the alignment on an alignment rig; the tyre that has already worn does not become regular again, so it is best to act as soon as you notice it.

Question 6

What is patchy or 'cupped' tread wear?

Accepted Answer

It is irregular wear in patches, with more worn areas alternating with less worn ones along the tread, which often produces noise and vibrations. Goodyear links these worn areas to worn shock absorbers or to the need for balancing and alignment. The mechanical cause must be identified: replacing only the tyres without fixing it exposes the new tyres to the same problem. In the workshop suspension, balancing and alignment are checked.

Question 7

What causes uneven tyre wear?

Accepted Answer

The main causes are incorrect pressure, alignment out of tolerance (toe and camber), worn shock absorbers and suspension, unbalanced wheels and a driving style with very hard braking and cornering. Failing to rotate tyres where the manufacturer provides for it can also lead to different wear between axles. To work out the cause look at the wear pattern: edges, centre, one side only or sawtooth point to different problems.

Question 8

When is a crack in the tyre sidewall dangerous?

Accepted Answer

Any visible crack deserves a professional check: small superficial micro-cracks due to age are different from cuts or deep cracks that reach the ply. Continental states that a tyre with cracked, deteriorated rubber or exposed cords cannot be repaired and must be replaced. If you see deep cracks, cuts or the internal structure, do not continue: have the tyre inspected by a tyre shop before setting off again.

Question 9

What should I do if I see a bulge or swelling on the sidewall?

Accepted Answer

Stop using that tyre and have it checked immediately: Michelin states that bulges and swelling on the sidewall can signal structural damage. They usually come from hitting a kerb or pothole, which damages the internal structure. The risk of sudden failure is real, especially at high speed, so the tyre generally has to be replaced. If you have to travel, fit the spare wheel or drive slowly to the nearest tyre shop.

Question 10

How can I tell if a tyre is deformed?

Accepted Answer

Deformation shows as a bulge, a dip or an uneven surface on the sidewall or tread, or is felt as vibrations that balancing does not remove. It may come from impacts, from damaged internal structure or from ovalisation after a long standstill. To check, the wheel is spun on a machine in the workshop: the operator detects radial and lateral run-out.

Question 11

How often should I inspect tyres by hand?

Accepted Answer

Once a month along with the pressure check, and before long trips. Look at the tread and sidewalls on both sides of the wheel (the inner one too, by turning the steering), look for cuts, bulges, cracks, foreign bodies such as nails or screws and uneven wear. Continental also recommends at least monthly checks. If something doesn't convince you, a tyre shop can assess it in a few minutes.

Question 12

How do I know it's time to change my tyres?

Accepted Answer

When the TWI indicators are reached, when unrepairable damage appears (bulges, deep cuts, cords, cracks) or when tyres are very old even if barely worn. Driving signs also count: more noise, vibrations, reduced grip in the wet. The decision depends on wear, age and condition, not on just one of these factors: a check in the workshop clarifies the situation in a few minutes.