Computer Aided Engineering (CAE) FEA Case Study: Boundary Conditions
Boundary conditions complete the FEA model 
Loads: Using Newtonian principles, an impact produced an acceleration of 100m/s/s of the total unsrpung mass (50Kg), giving a 5kN load. Plus the static mass of the car (500Kg) - another 5kN giving total load of 10kN. This was applied as a total pressure (which act at surface normals) onto the tyre contact patch - bottom of the picture above. To simulate air pressure of 32lb/in^2, applied as an intensity to all the inside wheel and tyre surfaces, after first converting to the units of this simulation which are mN/mm^2. In this case 32lb/in^2 = 225.454 mN/mm^2.
Contraints: The wheel's mating surface with the hub was contrained in Z (depth) translation and rotation. This was used for the base of the spring element, where it meets the coincident point of the rigid elements, generating an infinitely stiff pseudo hub. (Impossible, but will generate more loads in the wheel, which is good). The top of the spring element was constrained in all 6 degrees of freedom, simulating an infinitely stiff chassis. (Good, as before).