for wheels i wouldn't go wider than 7.5" or with more of an offset than +40 ... i'm really not sure about the 18"s with a drop though. hopefully someone on here has done that and can help you more than i can. as for the tires, i pulled this off of
www.whalentire.com (nice prices!) - you can draw your own conclusions. sorry for the caps, it's what they used.
STOCK TIRE SIZE: 195/65R15
DIAMETER: 25.0" SECTION WIDTH: 7.7" SIDEWALL HEIGHT: 5.0"
MINIMUM RIM WIDTH: 5.5" MAXIMUM RIM WIDTH: 7.0"
REVOLUTIONS PER MILE: 808
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SELECTED TIRE SIZE: 225/40R18
DIAMETER: 25.1" SECTION WIDTH: 8.9" SIDEWALL HEIGHT: 3.5"
MINIMUM RIM WIDTH: 7.5" MAXIMUM RIM WIDTH: 9.0"
REVOLUTIONS PER MILE: 805
IF YOU TRAVELED 60 MPH WITH THIS TIRE INSTALLED ON YOUR VEHICLE YOUR SPEEDOMETER WOULD READ 59.7 MPH
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SELECTED TIRE SIZE: 215/40R18
DIAMETER: 24.8" SECTION WIDTH: 8.5" SIDEWALL HEIGHT: 3.4"
MINIMUM RIM WIDTH: 7.0" MAXIMUM RIM WIDTH: 8.5"
REVOLUTIONS PER MILE: 815
IF YOU TRAVELED 60 MPH WITH THIS TIRE INSTALLED ON YOUR VEHICLE YOUR SPEEDOMETER WOULD READ 60.5 MPH