Complex sentence: The 1953 Grand Prix motorcycle racing season was the 5th F.I.M. Road Racing World Championship season, with nine Grands Prix and five classes, 500cc, 350cc, 250cc, 125cc and Sidecars 500cc.
Split into simpler sentences: The 1953 Grand Prix motorcycle racing season was the 5th F.I.M. Road Racing World Championship season. The season consisted of nine Grand Prix races in five classes 500cc, 350cc, 250cc, 125cc and Sidecars 500cc.