They play a frontline role: they keep the car firmly adhered to the road, support its weight, and must ensure an effective response to steering commands. For safe driving, choosing the "right" tires is essential. Each tire carries a series of codes that describe its characteristics and provide instructions for its correct use. Let's look at the first two.
Load Index
The load index is the numerical code indicating the maximum load (weight) that the tire can support when inflated to the reference pressure; an overloaded tire can overheat and suddenly collapse. Some tires also bear the words Extra Load or Reinforced. In this case, these are reinforced tires, capable of supporting—when inflated to the specified pressure—higher loads than normal tires of the same size. Due to this characteristic, they are typically used on heavier vehicles, such as SUVs.
Tires of the same size can have different load indexes. Regulations require fitting tires whose load index complies with the car manufacturer's specifications, in reference to the indicated sizes. But what if I decide to replace a tire with one that has a higher load index? Be aware: the individual tire can bear more weight, but for safe travel, the vehicle's maximum axle load capacity, indicated by the manufacturer, remains the absolute limit.
Speed Rating
The speed rating—expressed by a letter—indicates the maximum speed at which the tire can support the maximum indicated load. To determine which speed each letter corresponds to, a table is referenced: it goes up to "Y," which indicates a maximum permitted speed of 300 km/h.
It is possible to replace tires with others that have a higher speed rating than that indicated in the vehicle's registration document, but not the other way around. It is forbidden—in fact—to fit tires with a lower speed rating than that indicated by the car manufacturer, with one exception. Only during the winter season can winter tires with a lower speed rating than that indicated by the manufacturer for summer tires be fitted, provided that the code is not lower than Q (up to 160 km/h).
Choosing the "right" tires is essential for safety. And for another step forward, check out our article on "premium" tires, here.
