TREAD PATTERNS

The tread pattern decides many important properties of the tyre. Some being



rolling resistance, directional stability, steering control, braking, acceleration, water


dispersion and so on. Some tread patterns are discussed below. Typically, more the tread


depth less the braking distance and more the fuel consumption as rolling resistance


increases.


Another important feature is the rolling resistance which is measured in terms of


the energy the tyre consumes when it revolves and deflects. More rolling resistance


meant more energy consumption and less rolling resistance meant reduction in wet grip


performance. Replacement of some quantity of carbon black in the tread compound with


silica has enabled reduction of rolling resistance, better winter performance and better


wet skid properties all at the same time.


As stated grip and rolling resistance are contradicting requirements to be


satisfied. Technically speaking, grip deals with the distortion in the tyre at high


frequencies – or in other words on the degree of unevenness on the road and the number


of small stones it hits on the road. Good grip is given by rubber compounds which absorb


high levels of energy (high hysteresis compounds)


On the other hand, rolling resistance is affected by low frequency distortion – or


in other words the deflection of the tyre as it revolves. Low rolling resistance needs


compounds which absorb less energy (low hysteresis compounds)


The genius behind adding silica is that by doing so tyre engineers have created a


compound which has high hysteresis at high frequencies and low hysteresis at low


frequencies.
Rib treads – Tread patterns are in the form of parallel circumferential groove



(Here, circumference denotes that of the tyre).


The tyre has good lateral resistance so it has good directional stability and


steering control. Rib pattern is good for sustained high speeds due to less resistance to


forward motion (or less rolling resistance) and so less heat generation. But the tread


pattern has poor acceleration and grip on wet roads.


Used in paved road surfaces and bus or truck steer axles.






Lug treads – Tread patterns are in the form of grooves perpendicular to the


circumference of the tyre.


The lug tread pattern has excellent braking power and traction. Has very high


rolling resistance and is the main reason why it is not suitable for high speeds.


Used on dirt roads, rear wheels of buses, industrial vehicles and dump trucks.






Rib-lug treads – This is a combination of rib and lug treads.


The circumferential rib treads in the centre give good directional control while the


shoulder lug tread gives good braking and driving power.


Used for both paved and dirt roads and as both rear and front wheels of trucks and


buses.

Block treads – The pattern consists of independent blocks divided by



circumferential and lateral grooves.


Block patterns give good steering control on snow covered and wet roads and


water dispersal properties. Because of smaller tread blocks tyre wear is more.


Used for winter tyres.






Asymmetric treads – These tread patterns try to optimize the opposing properties


of dry grip and water dispersal. The tread pattern on the inner side has more grooves


giving better grip on wet roads. The higher plane surface area on the outer side are better


suited for high speed cornering due to greater contact area which also helps reduce tread


wear. Asymmetric tyres should always be placed the right way around.


Used in high performance and motor sport tyres.






Directional treads – This pattern is characterized by lateral grooves on both sides


of the tyre pointing in the same direction. They are designed to rotate in one direction


only so that many properties get optimized. They give good traction and braking


properties and have good stability on wet roads (which means good water dispersal).


Must be mounted in the direction of tread pattern.


Used in high-speed passenger car tyres.