The Gravity Shift has a lower RG core that will rev up sooner when it encounters friction, but it also has a pearl coverstock (and the box finish is polished), so it wants to slide more through oil and grab harder off the dry. It's a good 1-2 combination. When the lanes are oily, you probably would use the Attitude Shift, then switch to the Gravity Shift when you start to work in some friction on the lanes.
