If you use Rigid Dynamics, you don't need to use Modal Analysis first. You just import this geometry into the Geometry cell, then in the Model, create the joints and springs and import the input displacement as a joint load on the translational joint that connects the road body to ground. When you Solve, you will get a Transient solution and you can plot the displacement or acceleration of the car body and the wheel body.
You don't need a Fixed Support. The translational joint between ground and the road body, along with the input displacement load is equivalent to the fixed support.