That rim and tire fitment is a safe fitment on a TSX. You won't have problems with that. I would go to a 235/40/18 tire though, it will fill the guard slightly better giving a better look and increase the size of the sidewall giving a slightly better ride. You shouldn't have any problems getting a 235 tire on a 7" rim. You would still be able to lower the car with an Eibach or similar spring kit and still not have any problems.
is that going to affect speed and mileage significantly?
I am planning to put 235/40-18 on too, but the tire guy told me that it will affect fuel economy, more noisy, and he said doesn't matter if overall diameter is smaller 225/40-18 if the difference is less than 5%.
How about speed/acceleration... do you notice a difference esp. starting from a dead stop?
Sazabi you will have no problems with a 235/40/18 tyre, as long as you get the rim offset right. An 8 inch rim with an offset between 45-50mm would be perfect for this application. As for your "tire guy" with his "advice" the tread pattern of the tire will have a bigger effect on noise and the tyre pressure you run at would have a bigger effect on economy than the difference between a 225 and a 235.
Speed and acceleration are not going to be affected as the overall diameter is still very close to the standard size anyway, but the handling of the car is going to be better with a 40 series tyre with better rubber compounds and tread pattern design than the standard tyre. I have the Falken Ziex 326 and am very happy with them in the dry and wet.
woot! thank you EuroZ
combination I am planning to get is
235/40-18 tire with
18x7.5 offset +43
I think someone put the same size tire with +42 offset with no problem... so hopefully, +43 should be ok as well.