A recent SAE book (Gillespie, ref. 13., p 347-355) indicates that for bias-ply tires cornering stiffnesses are approx 12 % of the load on the tire (with a range of approx. 8%-18%) and radial tires cornering stiffnesses are approximately 15% of the load on the tire (with a range of approx. 11%-19%). There are also discussions in the book about the effects of inflation pressure (normally increasing the inflation pressure increases the cornering stiffness), tire size and width (larger size and width normally produces greater cornering stiffnesses), tread design and aspect-ratio (aspect-ratio=ratio of section height to section width, common vehicles ranged from 0.78 to 0.70, recent trends towards lower-aspect-ratio performance tires (0.60 and lower) on cars may produce cornering coefficients in the range of as much as 25% to 30% of the load on the tire). Please refer to that book for further information and references.