Step 1.  First you will need to load the Reactor toolbar.  Go to the Customize menu and choose Customize User

 Interface.  Select the Toolbars tab, pick the Reactor_light.cui and click Load, as in the image below.  

Step 2.  Create a spline shape in the left viewport similar to the one shown in the image below.  This will be the

Road for our Car.

You will need to apply an extrude modifier and adjust the amount spinner.  Then apply the normal modifier and

 flip normals.

Step 3.  Next we will use a Teapot primitive as our Car body.  Create a Teapot in the top viewport.  Under

 Parameters, set Radius to 15, as in the image below.

Step 4.  Now we need to create 4 tires for the Car.  We will use cylinder primitives: you can create them in

the Left viewport, as in the image shown below.  Set the Radius parameter to 8, the Height to 4 and the Sides

 to 5.  That way when the tires rotate we can easily see them moving.

Step 5.  On the Reactor toolbar on the left choose the Rigid Body Collection icon.  It's the first one

on the toolbar at the top.  Create this in the top viewport.  Next select the modify panel and ADD

all objects to the list, as in the image below.  This is required for the Reactor simulation to occur.

Step 6.   To make objects move and react in a simulation they must be assigned a Mass value.

Go to the 3ds max Utility Panel and choose Reactor.

Choose the Teapot object and under Physical Properties assign it a Mass value of 30, as in the image below.

Choose each tire and give it a Mass value of 40.  

Choose the spline and select "Use Mesh" . Since we do not want the Road to move we will not assign any Mass to

the spline object.

Step 7.  Now we will use the Reactor Toy Car System.  On the Reactor toolbar choose the Toy Car System icon ,

which looks like a red car.

Place the icon in the top viewport: the key here is to make sure the placement of the Toy Car System icon faces the same

way as our "teapot car" faces.  

Next go to the Modify Panel for the Toy Car System.  Add the Teapot as the Chassis and Add all four cylinders as

Wheels.  Set Suspension to 0.03 and make sure "Allow Wheel Penetration" is checked, as in the image below.

Step 8.  Finally, we need to test the simulation in the Reactor Preview Window.  On the Reactor toolbar

choose the icon Show In Window: it is highlighted in the image below, on the lower left.  This will bring up a

 Preview Window.

C hoose the the Physics Menu and select Realtime.  Then choose the Simulation menu and select Play.  

After testing this simulation you can go back and experiment with other Toy Car System settings to get different

 results.  The key here is to have fun!