Looking at a tire's spec sheet can be helpful. Here's one for the Direzza ZII:
Dunlop Direzza ZII
You will see that 235/40 is not approved for 7.5" wide. Although you could run 235/45 or 245/45. Take a look in the wheel fitment thread, as your offest will dictate how much clearance you have to the coilover/strut and therefore the tire width you can run.