Tyres are classified according to their construction as:
- Bias or Diagonal or Cross Ply.
In Radial tyre, ply cord, either steel or fabric, run straight across the tyre from bead to bead. In addition, the radial tyre has a belt of additional plies, usually steel running down the centre of the tyre between the carcass and the tread.This construction allows the radial sidewall to be much more flexible while the tread is much stiffer than bias ply tyres.This allow the tyre to absorb impacts and limit sideways movement of the tread while cornering.
In the Bias ply tyre, also known as diagonal ply tyre, plies run from bead to bead at an angle (hence the name bias).With layers of plies criss-crossing each other.This construction makes the sidewall relatively stiffer and the tread area softer.