I only casually looked at the weights when ordering my wheels and tires. They looked close so I didn't give it much thought. On closer look it looks like each wheel/tire combo is about 2.5lbs heavier than the stock setup. I guess that adds up! I'm sure the wider contact patch and slightly stickier "performance" tires add to it as well.
2011 V6 Base Grabber Blue GBMR #082
DG Custom Side Mirrors, Tri-bar Fender Emblems, MCA Grille, Magnaflow Street Axleback, Strut Tower Brace, AM GT500 Wheels, Bama Tuned 93Race