In radials tyres the ply or ply cords are alligned at 90 degrees to the circumference. While radials improve performance the fact is that they are not very good for bad roads and overloading. The suspension of a vehicle has, also, to be modified to accept radials. Radials offer much better grip of the road especially on surfaces which offer poor wheel traction like wet of slippery roads. The beauty of the radial design is that it separates the functions of the sidewall and crown of the tyre, allowing greater vertical flexibility whilst ensuring that there is still as much surface in contact with the road as possible. In classic radial tyres the sidewall has a one or two layers of textile cord giving good flexibility, and the tread is made rigid by combining the casing layer with two (or more) layers of steel cord bracing plies. Both these factors give the classic radial tyre excellent road holding capabilities and a longer life span when compared to vintage cross-ply tyres.