Need new tires for 2004 coupe 18" OEM rims. They say 225/45 front and 245/45 back.

Do i have to stick with these specs .. or can i go wider. Anyone recommend going lower profile .. maybe /40? .. suggestions would be much appreciated since I gotta get them asap.

I say stick with those sizes, if you go lower profile make sure you get wider tires or the odometer will be off.

Use this:
http://www.1010tires.com/TireSizeCalculator.asp