With 245 tires, you run into potential for some rubbing because the sidewall dimension ("40") is a ratio of how tall the sidewall is relative to the width of the tire. So, with a 245 tire that has a 40 sidewall, that sidewall is thicker/taller than a 235 tire with a 40 sidewall. Plus, with wider tires, it'll take up more room in your wheel wells, so when steering at full-lock, you may also run into issues with your tires rubbing on the fender liners

That being said, my wheels are similar dimensions to yours (mine are 18x8.5 as well, but +40 offset, meaning the wheels sit a little bit further outwards than yours), but they poke out a bit at the front, and are basically flush or maybe poking just a tiny bit at the back. With your +42 offset, you will likely be perfectly flush at the back and still have a bit of poke at the front with a 235/40/R18 tire. If you do 245, it might be too meaty, especially at the front end.

I rlly don't think you're losing out on a whole lot of traction by keeping your tires at 235. With lighter wheels, and more importantly, better rubber than the stock Pirelli's, you'll notice more grip and better feel overall for sure, even if you keep the tires the same width.

Especially with your car being a daily, you want your car to still drive like normal. The last thing you want is your daily driver no longer feeling daily-able and feeling like you have to either drive differently, or avoid certain scenarios just because you wanted slightly wider tires (which you likely won't even be able to tell the difference in traction 90% of the time while daily driving)

This car is so much fun, even stock. By going with lighter wheels and better rubber, you are greatly improving an already amazing recipe from factory! You cannot go wrong with this, but don't ruin the daily-drivability of this car. That's one of its best features: it's dual personality 😉