I'm planning on buying tires, the fronts are 245/30zr 20 and rears are 295/25zr 20. will there be an issue with the height difference? the vehicle is a 2012 s5, thank you

 

The basic rule with awd is that all four tires must have the same diameter (unless the vehicle was designed for a staggered setup with different diameters front and rear). If your car came from the factory with the same tires sizes front and rear,you will ruin the awd system with different diameters front and rear.