A toothed power transmission belt suitable for use in contact with oil, having an elastomeric belt body, a helical wound tensile member embedded therein, and teeth on a pulley-contact surface with a jacket covering the teeth, wherein the jacket is a woven fabric with a smooth, continuous, outer rubber layer formed from a nitrile-containing elastomer compounded with at least one coagent, an RFS adhesion promoter, and with no fluoropolymer, and the fabric has para-aramid fibers in the weft, meta-aramid fibers in the warp, and no nylon fibers.

Power transmission belts are disclosed that have a body made of a first elastomeric material, a plurality of cords embedded in the body of the belt, a back and a plurality of ribs or teeth. The back, ribs, or the teeth are covered by a covering material of woven fabric, knitted fabric, and non-woven fabric, which is treated with a treatment composition that includes polyurethane, polytetrafluoroethylene, and polycarbodiimide.

Power transmission belts are disclosed that have a body made of a first elastomeric material, a plurality of cords embedded in the body of the belt, a back and a plurality of ribs or teeth. The back, ribs, or the teeth are covered by a covering material of woven fabric, knitted fabric, and non-woven fabric, which is treated with a treatment composition that includes polyurethane, polytetrafluoroethylene, and polycarbodiimide.