I think the reason that is said is because bias ply tires have less compliance than radial tires. On a car with 4 tires of equal size, this could through off suspension tune and make one end of the car ride rougher than the other end. It would also definitely cause an alignment issue if you ran different types of tires on each side, but since that's not the case on our cars, it's not an issue.
With the fact that we are already changing handling characteristics by putting much skinnier tires on the front than on the rear, I believe the Bias ply tires are only going to positively affect things since they make up for the deficiencies of having an excessively small radial tire trying to support a load much greater than its size is suited for.
With the fact that we are already changing handling characteristics by putting much skinnier tires on the front than on the rear, I believe the Bias ply tires are only going to positively affect things since they make up for the deficiencies of having an excessively small radial tire trying to support a load much greater than its size is suited for.