When temperatures drop and the road surface is covered with a film of ice or slush, the only connection between the car and the asphalt remains the four patches of contact area, each the size of a human palm. But during the cold months this is especially important, and it is for this reason that controlling the wear of winter tires is not a matter of subjective judgment, but a critical safety requirement.
The first and most important indicator of suitability is the tread depth. The critical limit below which a winter tire loses its performance characteristics is exactly 4 mm. At values below this threshold, the grooves of the gripper are no longer able to effectively remove water and snow slurry from the contact patch, which dramatically increases the risk of aquaplaning. If at the beginning of the winter season the measurement shows a value of about 4 mm, the replacement should not be postponed, since during the operation the grip will fall below the permissible minimum.
The wear geometry also reveals hidden defects in the chassis. When the grip wears asymmetrically, in spots or mainly on the outer and inner edges, the cause usually lies in incorrect adjustment of the front or rear axle, compromised suspension or systematic driving with incorrect pressure. Even if the total tread depth seems formally within the norms, such a set reacts unpredictably during sudden braking or a quick change of direction.
External physical deformations require an immediate response. The appearance of bulges or so-called "hernias" on the sidewall means a torn internal cord structure. Such damage is not subject to any repair and makes the tire unusable, since there is a real risk of sudden bursting while driving. Similarly, deep cracks in the rubber compound, most often caused by improper storage in a dry and hot place or natural aging of the material, threaten the structural integrity of the entire set.
An extremely important factor that many drivers overlook is the age of the tire, indicated by its DOT code on the sidewall. This four-digit index indicates the exact time of production - the first two digits indicate the week, and the last two - the year of production. Over time, the chemical composition of the rubber hardens and loses its elastic properties necessary for low temperatures. Even a tire with good grip, whose DOT code indicates an age of more than 5 or 6 years, no longer guarantees the necessary traction on snowy roads, as the material becomes too hard.