Originally Posted By: Astro14
I think the floor jack rolls for two reasons: first, the lifting pad moves in an arc, so the wheels have to roll in response. Second, the part of the car being lifted moves ever so slightly because it too moves in an arc.

The first is the nature of a floor jack. The next would affect the scissor jack as well. Every time I have used a scissor jack to change a tire, it has tilted slightly when raised. I don't trust them for anything but an emergency...

Yeah this. If the base doesn't slide the top of the scissor jack will fold over the pinch weld on your rocker panel. Something's gotta give.