Synchronous drive belt

In combination (A) an endless synchronous drive belt comprised of a resilient elastomer, reinforced with one or more reinforcing members extending along and thereby defining a pitch line, with a succession of identical teeth, each having a tooth depth, uniformly spaced apart by their pitch P and having fore and aft flank surfaces, the space between adjacent teeth defining a land area having a centerline and lying below a land line L and a tooth root radius which inscribes a 90.degree. arc which forms the transition between the land line and a tangent to the flank surface perpendicular to the land line and has its center in said land area, the distance between said land line L and said pitch line defining a pitch line differential, wherein each said flank surface is shaped in longitudinal cross-section as an arc of a circle with a radius R having its center located in said land area no further than said centerline away from its opposed flank and below said land line from a distance equal to said tooth root radius up to one half said tooth depth;

• and (B) a pulley having a plurality of identical peripheral belt-engaging teeth defining between themselves pulley cavities, each pulley cavity having a fore and an aft flank surface shaped in cross-section as the arc of a circle with a radius R' having its center located within the pulley tooth no further than a radial centerline of said pulley tooth away from the opposed cavity flank and radially inward from the pulley tooth tip, a distance equal to or greater than the belt tooth root radius, wherein R' is equal to or greater than R.