The radial ply tyres consists of two bead cores joined together radially via the carcass – hence the name radial tyres. A belt of cords provides the necessary stiffness , whereas the external part of the tyre consists of the tread and sidewall and the interior of the inner lining, which ensures the tyre is hermetically sealed In passenger car tyres, the carcass is made of rayon or nylon, the belt of steel cord or a combination of steel, rayon or nylon cord, and the core exclusively of steel. Due to the predominance of steel as the material for the belt, these tyres are also known as ‘steel radial tyres’. The materials used are indicated on the sidewall . In commercial vehicle designs this is particularly important and the carcass may also consist of steel
The stiff belt causes longitudinal oscillation, which has to be kept away from the body by wheel suspensions with a defined longitudinal compliance, otherwise this would cause an unpleasant droning noise in the body, when on cobbles and poor road surfaces at speeds of less than 80 km h1. The only other disadvantage is the greater susceptibility of the thinner sidewalls of the tyres to damage compared with diagonal ply tyres. The advantages over cross-ply tyres, which are especially important for today’s passenger cars and commercial vehicles in radial ply tyres, are:
- significantly higher mileage
- greater load capacity at lower component weight
- lower rolling resistance
- better aquaplaning properties
- better wet-braking behaviour
- transferable, greater lateral forces at the same tyre pressure
- greater ride comfort when travelling at high speeds on motorways and trunk roads.
In passenger cars, the tubeless tyre has almost completely ousted the tubed tyre. The main reasons are that the tubeless tyre is:
- easier and faster to fit
- the inner lining is able to self-seal small incisions in the tyre.