Originally Radial tires were not recommended to be X rotated. Just front to back. BUT, just about every car or truck manual that I look at now, recommends X rotating. (Unless you have a tire that is make to rotate in only one direction). I have found that if you do not X rotate, the tires will develop rough edges in one direction, that continue to get more noticeable. This will cause tires to make a loud noise, kind of a Whirring sound. I have seen tires so noisy that I have actually switched all 4 of them side to side to reverse rotation, to control noise.