I have a 62 Impala with 155X13 radial tires. When I get up to about 45 mph, the back end starts to sway. It is a little unnerving to say the least. I have heard that if I went to bias ply tires (520's), this will take care of the problem. I have replaced all the trailing arm bushings and had the car alined. The reason I heard the bias ply tires will help is that the sidewalls are alot stiffer. Any help on this would be greatly appriciated.