Steric effects play a major role in the assignment of configurations in cyclohexanes. One can use steric hindrances to determine the propensity of a substituent to reside in the axial or equatorial plane.  It is known that axial bonds are more hindered than the corresponding equatorial bonds. This is because substituents in the axial position are relatively close to two other axial substituents. This makes it very crowded when bulky substituents are oriented in the axial position. These types of steric interactions are commonly known as 1,3 diaxial interactions.  These types of interactions are not present with substituents at the equatorial position.
There are generally considered three principle contributions to the conformational free energy:
# Baeyer strain, defined as the strain arising from deformation of bond angles.
# Pitzer strain, defined as the torsional strain arising from 1,2 interactions between groups attached to contiguous carbons,
# Van der Waals interactions, which are similar to 1,3 diaxial interactions.