CLS 550 WITH 13000 MILES RWD

Your vehicle is RWD, but at 13K miles, check the wear on the left side tires. Depending on wear, I think I would put the new tires on the front of the vehicle, and rotate the left sides to the rear, so the worn tires don't induce vibration or shimmy in the steering. Check with your tire shop to see what they recommend. Tires should always be replace per axle, not side if you are replacing more than two.

I would want to know why the tires on one side wore out faster. Something is wrong. If you only replace two it should be the rear tires. If your car has staggered wheel/tire sizes then you can't rotate tires front to back and if they are directional you can't swap sides either.