The correct tyre operating pressure is normally shown in the owner’s manual. It is very important to maintain this parameter for a number of reasons, as it significantly affects:
• tyre life
• road holding
• fuel consumption
Pressure that’s too low causes:
• less grip and the risk of losing control of the vehicle, above all during emergency manoeuvres
• tyre overheating, with the consequent risk of bursting
• considerable wear on the sides of the tread, reducing tyre working life by up to 45% (European Commission data reported in a Federpneus memo)
• up to 4% higher fuel consumption and consequently increased environmental pollution and CO2 emissions
Pressure that’s too high causes:
• a smaller footprint and consequently poorer grip, traction and braking
• considerable wear in the middle of the tread
• a less comfortable ride for passengers
• more risk of damage from impact
As a result, tyre pressure should be checked regularly (at least once a month or every 10,000 km, and always before setting off on a long trip), without forgetting to check the spare tyre. This should be done when the tyres are still cold, as just a few kilometres’ driving or leaving the car out in the sun may distort the pressure reading.
When a car is parked for a long time, the tyres tend to flatten at the point of contact with the ground. Such deformations are normally only temporary and are therefore resolved after a few kilometres, when any vibrations produced will disappear. The longer the vehicle is left parked, however, the more chance there is that the damage becomes permanent, requiring replacement of the tyres.
To prevent these situations, tyre pressure should be increased before parking to 3.2/3.5 bars and, where possible, the vehicle should be moved periodically to change the point of contact.
It must also be remembered that prolonged contact with oils, diesel or solvents will seriously damage tyres, as these substances attack the compound.
With the passing of time, tyres tend to lose their characteristics of elasticity and adherence. A good remaining tread depth is not always a guarantee of perfect road grip. Indeed, as tyres age they generate less friction with the bitumen, meaning less wear yet, as a result, poorer grip.
Tyres don’t have a use-by date, however after 5/6 years the rubber’s chemical properties start to change, to an extent that is influenced further when the rubber has been exposed to factors such as: sunlight, pollutants (in city centres), strong sources of heat, solvents in general, etc.
Any cracks on the sidewall or on the inside of the tread (in the grooves that don’t come into contact with the bitumen) may be indicators of tyre ageing. You should always contact a specialist centre to have your tyres carefully inspected.
If a tyre has damage, cuts or bulging on the sidewalls or the tread, or has been involved in a violent collision, it should be immediately checked by an expert.
Bulging on the sidewall (also called the shoulder) of the tyre, for example, means that the casing is irreparably damaged, leaving no other choice but to urgently replace it; otherwise, in more serious cases, it may burst. Such events may be due to accidental impact, but also excessive load.
Naturally, visual inspection may be sufficient to identify more evident damage, however never forget to also check the inside shoulder, i.e. the part facing the wheel arch.
Remaining tread and tyre replacement
Every vehicle has its own specific mechanical, load and speed characteristics, and therefore tyres are chosen essentially based on these characteristics. As a result, the information provided by the vehicle maker on the registration documents must be complied with as regards size, load index and speed rating, which may be higher yet never lower (at least for summer tyres) than the values described.
The legal limit in Italy for tread depth is 1.6 mm, however manufacturers and experts suggest that tyres should be replaced before reaching 3 mm (4 mm for winter tyres), a threshold below which road grip is no longer guaranteed, especially in the event of rain or slippery roads.
All tyres (excluding spares for temporary use) fitted on a vehicle must have the same structure (e.g. radial). In addition, the same type of tyres must be fitted on the same axle.
To maintain optimum driving conditions, all four tyres should be the same and have the same degree of wear. This is especially important when using winter tyres, given their better grip in tricky climatic conditions (rain, snow, ice…). Finally, always remember to fit new tyres or those with the least wear on the rear.