TREAD PATTERN DESIGNS
Aside from the compounds used, the second biggest differential in tyre design is the tread pattern. There are thousands of tread pattern designs already available, and as tyre research and development continues manufactures are constantly producing new styles.
Arguably on smooth dry roads, slick tyres will offer the best performance because all of the tread area is in contact with the road. However, our roads are seldom totally dry, therefore the tread pattern needs to have the ability to clear water from under the tyre in wet conditions whilst still retaining as much dry performance as possible.
The different tread pattern designs available for road tyres can be easily split into three main categories; symmetrical, asymmetrical, and directional.
SYMMETRICAL TREAD PATTERS
Starting with the most simple, a symmetrical design is exactly as it says and features the same pattern across the whole tyre. This means the same tyre can be fitted the same way to any of the four wheels.
ASYMMETRICAL TREAD PATTERNS
An asymmetrical tread pattern differs across the width of the tyre, meaning the design has an inside and an outside edge and needs to be fitted accordingly. Asymmetrical tread patterns offer a couple of advantages over symmetrical designs. The first of which is the outer edge and shoulder area of the tyre usually features larger, stiffer tread blocks to help with cornering stability. This is because the outer edge of the tyre is subjected to higher loads than the inside when cornering hard. Asymmetrical patterns also tend to have an inner edge that features more tightly packed and more aggressive grooves. This helps with water dispersion and gives better performance and grip in wet conditions. Finally, asymmetrical designs can also feature a fairly wide continuous centre rib, which aids high-speed straight line stability too.
DIRECTIONAL TREAD PATTERNS
Directional tread patterns differ again from both symmetrical and asymmetrical designs. They are symmetrical across the width of the tyre (meaning they have no specific inside or outside edge) but have a design that only works in one direction of rotation (hence the name). This means the tyres can only be fitted to a pair of wheels (either left or right handed) and need to be turned around before fitting to the opposite pair.
Directional tyres offer different performance advantages to asymmetrical patterns, the main one being wet weather performance. The aggressive nature and number of grooves typically used on a directional pattern means it offers greater water dispersion than an asymmetrical design.
These deep directional grooves literally pick the water up from the centre of the tyre and throw it out of the sides, giving very impressive wet grip. In the dry the aggressive grooves have no water to disperse but the larger tread blocks offer a greater contact patch with the road than symmetrical tyres, therefore offering more grip.
The directional grooves used on this type of tyre also help reduce road noise and straightline stability, when compared with an asymmetrical pattern.
It is also possible to combine both asymmetrical and directional tread patterns to have a design that has both an inner and outer edge and a direction of rotation.
These style tread patters usually feature a stiffer tread block on the outer edge, similar to that of an asymmetrical tyre, but the pattern tends to incorporate aggressive grooves as with a directional tyre.
While talking about tread pattern designs it’s also worth noting the shoulder block area of the tyre. This is the area between the tread pattern and the sidewall, and takes the brunt of the car’s lateral forces during cornering. As a result these tend to be fairly chunky in their design, to maximise the contact patch with the road as the tyre moves around under heavy cornering forces. The grooves between the shoulder blocks are known as sipes, and their job (as well as helping to disperse water in wet conditions) is to help keep the tyre cool. The position of these sipes determines the size of the shoulder blocks, and these are deliberately spaced to ensure the shoulder blocks are not uniformly sized. Instead, the size of the shoulder blocks differs all the way around the circumference of the tyre, as this alters the harmonics of tyre and can actually reduce road noise. If the shoulder blocks were all the same size the tyre would produce an irritating hum when driving at a steady speed.
Symmetrical tyres are consider the ‘norm’, and are generally cheaper than asymmetrical or directional designs
Asymmetrical tyres have a design that differs across the width of the tyre