The battery is definitely smaller. It was discussed before as there were a couple of others using it. The battery needs to be left on a battery tender if the car sits more than a couple of weeks as the reserve capacity isn't as large as the huge battery that we carry. I use the stock mount, I just bent the small hold down tab in a vice to about a 30'-40' angle. As for the tire size weights, a search of Tire rack specs & manufacturers specs in 255/ 40-18 size in Michelin PS2 & the Dunlop Sport Maxx's that I am using to the 255/35-19 tires for the 19" wheels in stock size reveal the same or only 1lb increase. Tire rack says that even though you go down to a shorter sidewall and keep the same width (you would think you would get lighter in going up) that the tires weight the same or only slightly more because they tend to have more Steel cords in the sidewall than the taller sidewall sizes. So a 0 to 4lb gain is offset by a loss of 60lbs on the wheels.