Are you asking for feedback on the tire change, or a new wheel and tire package?
235/40-18 is a great tire size for a rotatable square fitment on the E9X chassis, and there are quite a few tires to choose from. We would argue that an 18x8.5" wheel would yield better results, but they would certainly work on the 8" wheels as well. The 8.5" wheels would provide more sidewall support leading to better performance (especially considering the fact that our 8.5" wheels are lighter than the stock 8" wheels), as well as a more aggressive stance (filling out the fenders a little more). No modifications are needed for either wheel and tire iterations on the stock suspension.
E9X 3 Series Fitment Guide
- Ryan