The 40's will suffice in the rear as long as you don't go too wide. You should be OK with the 275/40R19 and not rub fender wells, but how will it look? ... HMMM. But in any event, up front, any tyre taller and wider than 235/40R18 risks catastrophic conflict with the upper control arm nut.

As step one always, consider doing everyone a service and use the SEARCH function.

Regards.