Stay at 36,, it is the car that wants the 36, not the tire the 235/40-18 is 25.4 tall & side wall of 9.3,
to me it is too big for the front as u make a U turn they will rub but the real reason is at 100 mph the front end starts to lift..
With the stock tire on the front no lift,,(the front stock rim is 7.5 wide) -----225/40-18 is 25.1 tall & side wall of 8.9.
I have 235/40-18 on the front of my V8 (I did not put them on) I just changed to a 18x8.5 rim, et 30 with the 225/40-18
the stock rear rim is 19x9 wide . my new rear rims will be 19x9.5 et 28
I also have a rear set for the rear 18x9.5-18 tire is a 265/40-18 at 26.4 tall. :note the 235/35-19 are10.8 side wall & 26.6 tall perfect tire for the rear
Good luck with your set up, they should work great, just remember not to hit the turning stops when making a u-turn
OH here is the chart on the stock rims on all crossfires Jim
The stock rims on a Chrysler Crossfire (all model years 2004-2008) have the following specifications, which are consistent across the standard and SRT-6 models:

Specification Front Rim Rear Rim Diameter 18 inches 19 inches
Width 7.5 inches 9 inches
Offset 35 mm 22 mm
Bolt Pattern 5x112 mm 5x112 mm
Number of Lugs 5 lugs 5 lugs