Tires play a key role in car handling and safe driving. They are the only contact of the car with the road. Therefore, checking for their good condition and proper pressure is of paramount importance.

• Every now and then we have to change the car tires

The average lifespan of tires, under normal conditions, should be considered 4 to 4.5 years. The average number of kilometers traveled, before the need for replacement, is 50,000. Of course, these numbers are indicative. The mode of use (mild or aggressive driving), the roads on which the car moves, as well as the avoidance – or not – of extra intense stress (potholes, parking on sidewalks), obviously affect – positively or negatively – the average duration of life.

To judge if our car tires need replacement, we can go to a specialty store, but we can also make a pretty good assessment on our own with visual inspection. The points to look out for are, in order of importance, the following:

1. If a bulge has appeared somewhere in the tire, the tire needs immediate replacement. This bulge is an indication that, as a result of a blow, the reinforcing mesh inside the tire has been broken and there is an increased risk of “cracking”.
2. If the depth of the sole is less than 3 mm.
3. If cracks appear on the surface of the rubber, on the sides or in the grooves at the bottom of the sole.
4. If the date of manufacture (see below) is older than 5 years.

In all 3 cases above (except the first in which the need for replacement is immediate and urgent), traction on dry roads and much more on wet roads will be reduced and we will have to plan the replacement of the old car tires relatively soon. us.

• Symbols and numbers

On the side wall of the tires there are numerous symbols and numbers, which give all kinds of information about the characteristics of the tire (dimension, speed index, load index, date of manufacture, need or not to use a balloon, etc.). We will explain what is most important and useful for the average driver.

The most important alphanumeric symbol has a form like the following:

215/60 R17 96H.

The first number shows the width of the tread, measured in millimeters (the above tire has 215mm tread width). The second number shows the profile of the tire, ie it shows what percentage of the width of the tread is the side of the tire (in our example the side is 215 x 60% = 129mm.

The letter R is the initial of Radial and indicates the type of construction of the tire (radial).

The next number shows the rim dimension to which the tire is made to fit, measured in inches. We see that from these numbers it is easy to calculate the total height of the tire. In our example are:

17×25.4 (conversion of inches to millimeters) + 2x 215×60% = 689.8mm.

So if we are thinking of fitting different tires to the same or different sized wheels, we can easily calculate the total wheel height of the solution we are considering and decide, taking into account the total wheel height, when possible, to remain unchanged.

The next number is called the load indicator . The load index of a tire shows the maximum load that a tire can carry at the permitted speed and pressure conditions. Indicatively, the number 96 of our example, corresponds to a load of 710Kg.

The last letter is called speedometer and indicates the maximum speed at which this tire operates safely (indicative: T: up to 190 km / h, H: up to 210 km / h, V: up to 240 km / h, ZR: & gt; 240 km / h).

Another very important number that we should be able to read on the tire is its date of manufacture . This is always 4 digits (after 2000) and is at the end of a sequence of letters and numbers that always starts with the letters DOT (Department Of Transport). The format of the sequence is something like this:

DOT 7GER M6U T 2209

In the last 4-digit number, the first 2 digits indicate the week of manufacture of the tire and the last 2 the corresponding 2 last of the year of manufacture. The tire that has the above indication has been manufactured in the 22nd week of 2009.

The above indicators and numbers cover the most important information we need to know about the tire. Those of you who are interested in the … “fine print”, read below!

Treadwear – Traction – Temperature

On the outside (towards the sole) of the tire there are also the indicators: Treadwear (wear) – Traction (traction) – Temperature (temperature).

Treadwear : Takes values ​​from 60 to 700 in steps of 20. The higher this index, the greater the wear resistance (hence the lifespan) of this sole.

Traction : High traction indicates that the vehicle will stop at a shorter distance on a dry or wet road than another vehicle with lower tires.

Traction AA Index : The tire behaved perfectly on both surfaces. Traction Index A : The tire behaved satisfactorily on both surfaces. Traction Index B : The tire behaved satisfactorily on one surface. Traction Index C : The tire performed poorly on both surfaces.

Temperature : The temperature gauge calibrates the tire’s resistance to heat development which heat affects the tire life.

The final calibration is as follows:

“Temperature A” indicator : The maximum (and best) temperature indicator, which shows that during the test the tire withstood a speed of 187 km / h for half an hour.

“Temperature B” Index : The tire went 160 km / h for half an hour but not 187 km / h).

Temperature C Index : The lowest (and therefore worst) temperature gauge that indicates that the tire could not withstand 160 km / h for half an hour.

To be on the market a tire must have at least a “C” temperature rating.

Finally, you should be aware that each tire has built-in TreadWear Indicators (TWI) . These are raised points in the main longitudinal grooves of the tread, distributed in the circumference of the tire, which reach the same level as the rest of the tread at 1.6mm. There are usually 6 such markers on the perimeter of the tire and they are marked with either the letters TWI or an arrow. They help us understand when the depth of the sole has reached 1.6mm, which is the minimum required by law. However, we remind you that we should actually replace the tires much earlier, when the depth of the tread becomes less than 3mm.