The diffusion temperature of molecular 'walkers', molecules that are capable of moving unidirectionally across a substrate violating its symmetry, can be tuned over a wide range utilizing extension of their aromatic backbone, insertion of a second set of substrate linkers (converting bipedal into quadrupedal species), and substitution on the ring. Density functional theory simulation of the molecular dynamics identifies the motion of the quadrupedal species as pacing (as opposed to trotting or gliding). Knowledge about the diffusion mode allows us to draw conclusions on the relevance of tunneling to the surface diffusion of polyatomic organic molecules.