The dark geometrical relaxation of sterically congested diarylcarbenes under matrix conditions was studied by ESR using bis(2,4,6-trichlorophenyl)carbene as a test molecule. The initial decrease of the parameter D has been found to proceed independently from the well-known expansion of the cental carbenic angle. The latter manifested by the reduction of the parameter E appears to be in correlation with the molecular mobility of the immediate surroundings probed by the reorientation of the primarily aligned test carbene. The complicated nature of the geometrical relaxation of the test carbene was interpreted in terms of the competition of the release of the congestion at the carbenic center and the restraints imposed by a matrix cage on any geometrical changes of the guest molecule.