The construction of the tire has big importance for its overall structure, for strength, loading capacity, torsion and internal resistance, but it is the tread that makes the direct contact with the road. On the market you can find thousands of tread patterns where functionality and aesthetics are combined in different proportions. Of course, not always the one is at the expense of the other, but usually achieving both is quite difficult. The perfect tire for dry asphalt would be smooth, like slick tires for sports cars. This provides a maximum contact area of the tire with the road: of course, the grip depends on many other factors, as the kinematics of the suspension and the weight distribution.
The appropriate compound structure and tread pattern are crucial to satisfy multiple contradictory requirements – dry grip, wet grip, low noise level, low rolling resistance, wear resistance. Despite the many solutions in shaping the pattern basically it looks like this:
The ribs are connected to a common circuit of blocks that provide maximum contact area, and the shoulders provide good traction of the car during steering. The blocks have the same purpose as the ribs. The sipes allow relative displacement of the parts of the blocks and in the winter tires they are formed in a specific way, providing traction to snow. The main purpose of the grooves is to lead off. As water has the same properties as any liquid fluid, i.e. it is practically incompressible, the only way for contact between the tire and the road is to push out or lead off the water to the grooves. Tire manufacturers create more complicated and specific arrangements of the transverse and longitudinal grooves, as some of the longitudinal are independent and their purpose is to take some of the water, while other are connected with transverse grooves, which function is to lead the water from the front to the rear part and push it out. Recently, tire designers are striving to direct the water not out but inward and to the back. The ability of the tire to push a lot of water depends on the grooves depth and their size – which is in contradiction with the performance on dry surfaces, where the most important is to maximize the contact area and respectively the grip. Experts call the ratio of the area of the cut spaces, i.e. grooves and sipes, with the area ratio unfill or void ratio.