Chassis Length.
3Rods, It's my understanding that Chevrolet built the SSR on a Chevy Trailblazer chassis. The Trailblazer Ext. (extended) had a wheelbase length of 129 inches. They wanted the SSR to be a bit shorter so they removed 13 inches from the 129 in. Trailblazer chassis creating the 116 in. SSR wheelbase. They cut out this 16 in. section and then welded back the chassis and that's probably what you are looking at. I think ALL SSR's will have this same welded chassis.