Improved performance of arc coil springs by stress reduction when they are bottomed out is achieved by forming the coil spring wire in a substantially trapezoidal or other shape such that when bottomed, the side surfaces of the coil abut and carry the bottoming load which is distributed over a comparatively large surface area. The angles of the sidewalls of the substantially trapezoidal cross section wire are preferably coincident with lines of radius when the spring is installed in an arc in a clutch, damper or flywheel. The radius of the outer surface of the arc coil spring wire is matched to the radius of the inner surface of the guide or housing so that the area of contact is large, thereby distributing the outwardly directed spring force over a large area, reducing the force per unit area and improving lubrication retention on the contacting surfaces.