Hi and welcome to the forum. You need to add your location to your profile so we all know where you are since replies may need to be market specific. If I understand you correctly you want to increase the overall rolling diameter of your rim and tyre combination. It would help if you could explain why you feel you need to do this. MB have spent millions in determining the optimum rolling diameter for their GLC range and even then they have had to accept a compromise with RHD cars due to steering geometry issues. Surely any increase will immediately cause clearance problems requiring you to limit the turning circle to prevent fouling. Moving anything outside of the manufacturer's design parameters will impact efficiency. You will immediately invalidate your 3-year warranty and, of course, you will need to declare the modification to your insurer or you will find yourself driving without any insurance. If you are creating a "donk" car for perhaps customising/promotional purposes, you will know all this already.