i put two 245 40's 18 on the rear... and two 225 45's 18 on the front... and i found that that had made the car accelerate quicker and steering more flexible... is this goood or is my car about to fall apart?! im thinkin its fucken waaay swwweeeter!!!

 

Your car will not fall apart. 225/45R18 and 245/40R18 are about equal in diameter.
I'll expect to get my 245/40R18 Michelin PS2s next week.