Check into getting the eibach lowering pro kit
OP has not been online since Jan 2017If you go to a 235 you should go to 40 series or the larger diameter will have adverse effects on mpg and acceleration. Probably should look into 245/40-18, wider and not taller. Tire Rack has charts to compare dimensions of the tires they sell. Might possibly need spacers so you don't create rubbing on the inside.