They can and most likely will slip and scratch the surface. I suggest cutting up an old floor mat with the vinyl or rubber-like backside to place the ramps on to reduce any slippage. The one ramp I know that will not slip are Race Ramps.
An old piece of carpet can work wonders to protect a floor from tires. Shea is correct, ramps can slide and scratch, but we have seen people affix them with double sided tape and that seemed to stop the issue.
