Winter tyres to small rims ? – Vibrations S90

Hello, I want to tell you something about my winter tires here and at the same time listen to your experiences. Have had an S90 R design since summer and have now my first season WR on it. These have been raised to 8×17 Rial M10. Pneu is a GoodYear Ultra Grip. Since the beginning of the switch to WR I have had a restlessness in the FW. Did not have my tyres balanced out at two dealers. It had not both the same result – it means that the second workshop had to correct the work of the first workshop. A slight imbalance always persists. Now the best thing: was with my and had to find out there today that my tyres were too small for my vehicle without air suspension and that technically it is now so conditional with the long wheelbase. Did you ever hear such a thing? KBA allows a rim and then despite balancing still a restlessness?