could be a few things that factor into this sort of issue.. bent rim, off balanced rim, mis matched tires, alignment slightly off, Axle is out of balance, warped rotor, bad motor mount...
DO a visual inspection of motor mounts if they are good that is easiest item to check off.
check your tires to make sure they are all wearing evenly.
last just go to an alignment shop and get everything checked straightened and balanced.