Answer 1.
Ordinary tyres or cross-ply tyres are the oldest type of tyre and has a case made of two or more layers of fabric. A tyre’s strength and load carrying ability were at one time indicated by its number of plies. Modern materials and man made fibers such as polyester and glass fiber embedded in the rubber are much stronger than the cotton fibers originally used.
Radial tyres give the impression that they have low inflation even though the air pressure is as recommended by the manufacturer. This is primarily because of the soft sidewalls. The physical difference between the radial and cross-ply tyres and in their behaviour on the road is governed by the difference in their individual carcass construction.
Carcass is the rubber-bonded cord structure of a tyre integral with the bead and contains the inflation pressure. The radial ply has a stiffness and resistance in its tread area, so that in motion the tread in the contact patch retains virtually all of its pattern and grip.
Radial tyres normally give twice as much mileage as cross-ply tyres and the difference in cost is not more than 30 percent sometime even less and give a marginally harder ride but are safer at high speed.
Radials make the steering a little harder than cross-ply tyres, but provides better braking performance. The carcass of cross-ply tyres consists of textiles cord ply fabric, but in a radial tyres it consists of steel belted cord laid substantially 90 { + o) to the centre line of the tread.
Answer 2.
Tyres consists of layers of cord called ‘plies’. Plies are shaped on a form and impregnated with rubber. These are two ways to apply the plies on the bias and radially.
In bias type (ordinary) tyres the plies are criss – crossed. One layer run diagonally one way and the other layer runs diagonally the other way. The arrangement makes a carcass that is strong in all directions because of the overlapping plies. However the plies tend to move against each other.
This movement generate heat, especially at high speed. Also the tread tends to ‘squirm’ or close-up as it needs the road. This increase tyre wear. Tyres with radial plies were introduce to remedy these problems.
In radial tyres, all the plies run parallel to each other and are vertical to the tyre bead. Belts are applied on the top of the plies to provide added strength paralleled to the bead. The radial tyre gives better fuel economy and lesser tyre wear.