A tyreis composed of several parts.
The tread is the part of the tyre that comes in contact with the road surface. The part which is in contact with the road at a given instant in time is the called the ‘contact patch’. The tread is a thick rubber, or rubber/composite compound created to provide an appropriate level of traction that does not wear away too quickly. The tread pattern is characterized by the geometrical shape of the grooves, voids , lugsand sipes. Grooves run circumferentially around the tyre, and are required to channel away water. Lugs are the part of the tread design that contacts the road surface. Voids are spaces between lugs that allow the lugs to flex and evacuate water. Tread patterns feature non-symmetrical (or non-uniform) lug sizes circumferentially so as to minimise noise levels at discrete frequencies. Sipes are valleys cut across the tyre, usually perpendicular to the grooves, which allows for the water from the grooves to escape to the sides in an effort to prevent hydroplaning.
Tread lugs provide the contact surface necessary to provide traction. As the tread lug enters the road contact area, or footprint, it is compressed. As it rotates through the footprint it is deformed circumferentially. As it exits the footprint, it recovers to its original shape. During the deformation and recovery cycle the tyreusesflexible forces into the vehicle. These forces are described as Force Variation.
Tread voids provide space for the lug to flex and deform as it enters and exits the footprint. Voids also provide channels for rainwater, mud, and snow to be channeled away from the footprint. The void ratio is the void area of the tyre divided by the entire tread area. Low void areas have high contact area and therefore higher traction on clean, dry pavement.
The rain groove is a design element of the tread pattern specifically arranged to channel water away from the footprint. Rain grooves are circumferential in most truck tyres. Many high performance passenger tyres feature rain grooves that are angled from the center toward the sides of the tyre. Some tyre manufacturers claim that their tread pattern is designed to actively pump water out from under the tyre by the action of the tread flexing. This results in a smoother ride in different types of weather.
Tread lugs often feature small narrow voids, or sipes, that improve the flexibility of the lug to deform as it traverses the footprint area. Off-road Tyre enthusiasts have been sipingtyres for years for greater traction, as many manufacturers now offer already siped off-road-tyres.
Wear bars (or wear indicators) are raised features located at the bottom of the tread grooves that indicate the tyre has reached its wear limit. When the tread lugs are worn to the point that the wear bars connect across the lugs, the tyres are fully worn and should be taken out of service.
The bead is that part of the tyre that contacts the rim on the wheel. The bead is typically reinforced with steel wire and compounded of high strength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tyre holds air without leakage. The bead fit is tight to ensure the tyre does not shift circumferentially as the wheel turns. The width of the rim in relationship to the tyre is a reason in the handling characteristics of an automobile, because the rim supports the tyre's profile.
The sidewall is that part of the tyre that bridges between the tread and bead. The sidewall is largely rubber but reinforced with fabric or steel cords that provide for strength and flexibility.
The shoulder is that part of the tyre at the edge of the tread as it makes transition to the sidewall.
Plies are layers of relatively inextensible cords embedded in the rubberto hold its shape by stopping the rubber from stretching in response to the internal pressure. The orientation of the plies plays a large role in the performance of the tyre and is one of the main ways that tyres are classified.
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