Speed distribution measurements have been carried out of the hyperthermal methane molecular beam reflected from a Pt(111) surface as a function of the incident kinetic energy of the molecule and the surface temperature. Obtained results are found to qualitatively agree with the expectations derived from the Hard Cube model (HCM) calculation. The departure of the experimental results from the expectation increases with increasing the incident kinetic energy as well as increasing the surface temperature. This is considered to be due to the presence of adsorbates produced during the decomposition processes of the hyperthermal methane beam at the surface, which decreases the effective mass of the surface atom and increase the surface "roughness".