RADIAL TYRES

Most steel belted radial tyres are made of an inner liner, two polyester reinforced



body plies, two steel beads, two bead reinforcing strips, two chafers or anti – chafing


strips, two steel belts, two sidewalls and the tread. Some tyres also have one or two layers


of nylon or polyester reinforced sheets just below the tread and above the steel belt.


These are called “safety belts” or “cap plies”.






Radial-ply technology versus Bias –ply technology






Technically, these two variants differ in the way the ply cords (which means the


layers of fabric that makeup the body of the tyre) are layered in the body of the tyre. In


bias tyres the ply cords are at an angle to the direction of rotation or diagonally across the


tyre from bead to bead. These ply layers alternate in direction to reinforce each other.


On the other hand in radial tyres the ply cords are perpendicular to the direction of


rotation or run radially across the tyre from bead to bead. This means that they run


parallel to each other from bead to bead (with each individual cord running up the


sidewall, across the tread and down the other sidewall). This results in a cooler running


tyre that has more sidewall flexibility and better directional stability.


One common characteristic in belted bias-ply tyres and radial tyres is the need for


stabilizer belts made of sheets reinforced with fiberglass, steel or kevlar.


One difference between the multi – ply tyre and the belted tyre is the property of


the steel cord that is used. In the former, the fatigue life of the steel cords will be the


dominating aspect while in the latter; the stiffness will be of primary concern.


Performance wise, radial tyres surpass bias tyres when it comes to smooth rides


on bumpy roads and tyre grip on wet road conditions. Other plus points for radial tyres


are better braking and cornering power, better gas mileage and a higher life expectancy.






The strongest possible bond between the rubber and the steel belt wire is critical


in the construction of steel belted radial tyres. The most common failure mode of steel


belted radial tyres is separation in components in the area where the steel belt is placed.


During tyre usage, this area is subject to heavy stresses. Combined with the fact that


rubber adhesion to metal (here steel) is very weak makes this area prone to failure in


terms of separation of tyre components. Other factors affecting adhesion are mishandling


of components during usage and storage, accumulation of moisture on the steel belts


during processing, formation of pockets of air near the steel belts, contamination and last


but not the least undercuring.