Roll Rate/ Roll Stiffness is the measure of a racing car’s tire behavior, describing how the tire responds to roll and maintains contact with the racing surface. And is denoted by KΦ. Roll Rate/ Roll Stiffness is usually measured using the Newton Meter per Radian for Torsion Constant. Note that the value of Roll Rate/ Roll Stiffness is always positive. Typically, the value of Roll Rate/ Roll Stiffness is greater than 0.