The stock 18" are basically 29.58x9.65 tires (245/60 18) so you could find lots of 29x9.50 tires out there that should fit. Anything bigger would require a speedo recalibration, but I imagine that an inch bigger (30x9.50) should fit without rubbing. There's an easy and quick lift we can do by twisting a torsion bar, provides about 2" of lift I read: http://www.vehicross.info/forums/sho...=&threadid=738

That should easily let you fit 31" tires I'd imagine, right?