i'd sooner say to go with a 245/45/18 (this is the stock rear tire size) all around then to go with a 224/45/18 in front.
generally you want to stay within 3% of the stock diameter. the 245/45 leaves you .0645% different(smaller) and the 225/45/18 leaves you at 3.28% smaller diameter.
see the picture for reference
