A frame rail for a vehicle that is provided between vehicle frame and the bumper of a vehicle that has a thickness that varies from the front end of the rail to the back end of the rail. The compressive strength of the rail increases from the front end of the rail to the back end of the rail. The rail is rectangular in shape and the thickness of the rail is continuously increased to improve progressive crush characteristics of the rail under an oblique loading. A rail may be provided by providing a tubular rail having a plurality of ring shaped segments that have incrementally increasing thickness. Alternatively, the rail may have a uniformly increasing thickness from the front end to the back end.