Ditriptycilmethanes are known as molecular bevel gears because the two triptycil groups show correlated rotation. In this report, molecular bevel gears bridged with a group 14 element, bis(methyltriptycil)X (X = SiH2, GeH2, GeF2), were synthesized, and their gearing properties were investigated. Gear slippage, that is an error in gear rotation, is observed in high-temperature solutions of molecular bevel gears. Heavy atom derivatives undergo gear slippage more easily due to the long bond lengths and wide angles between the two triptycil units and the bridging group 14 element. Activation energies of gear slippages were estimated by temperature-dependent NMR spectroscopy and DFT calculations, and theoretical thermodynamic parameters for gear slippage were found to be in excellent agreement with experimental values. The results indicate that theoretical calculations for gear rotation in molecular bevel gears can accurately reproduce experimental phenomena.