Abstract: A stock rubber is provided with chopped aramid fibers and chopped polyester fibers blended in the rubber component, which is EPDM. The chopped polyester fibers are longer than the chopped aramid fibers. A transmission V-belt is obtained and molded from the stock rubber. When molding, the chopped aramid fibers and the chopped polyester fibers are oriented in a width direction of a belt body of the V-belt.

Abstract: Noise and vibration of a helically-toothed-belt transmission device driven under heavy load or at a high-speed rotation, are reduced. A backlash “D” is selectively enlarged in a helically-toothed-belt transmission device that transmits drive force by meshing between a helically toothed belt and a helically toothed pulley. That is, a tooth helix angle “?” is set in a range of ?0.2?1?W·?/Pt?0.75, with “Pt” being a tooth pitch, “?” a tooth helix angle, and W the width of the belt. The backlash “D” between the helically toothed belt and the helically toothed pulley is set to be 1.6%-3% of the tooth pitch “Pt”.