The belt construction is formed mainly of polymeric material, and has rounded top and bottom teeth respectively extending along the length of the top and bottom surfaces of the belt construction, the belt construction comprising a tension section (29) having the top surface (30), a compression section (31) having the bottom surface (32), and a load-carrying section (33) disposed intermediate the tension section and the compression section. The bottom to top tooth pitch ratio (45 to 44) of the belt construction (28) is approximately 1.40, and the bottom to top tooth depth ratio (47 to 46) thereof is approximately 1.77, while the belt thickness (42) to flex thickness (43) ratio thereof is approximately 3.98.