A comparative evaluation is presented of the performance of two types of materials with different yield strengths both of which currently are used in heavy duty truck frames. These two materials are an as-rolled 80 ksi yield strength low alloy steel (VAN-80) and a 110 ksi yield strength low carbon, intermediate manganese, quenched and tempered steel.The evaluation consists of a full size siderail fatigue life evaluation, fatigue performance of smooth and notched specimens tested in load control, fracture toughness data and fatigue crack propagation rates down to -60°F for each material, and an analytical treatment to establish the critical event that leads to failure in a structure at low temperature.As truck frame siderails must provide reliable performance over a prolonged service life, they must demonstrate a high resistance to fatigue. A discussion of the conventional R.B.M. rating of a frame siderail related to its fatigue performance based upon the results of the fatigue evaluation is presented.The use of “as-rolled” high strength material yielding equivalent in-service performance to a quenched and tempered product offers significant benefits to both user and manufacturer. This product is both cost effective and energy effective in that the additional processing through conventional heat treatment systems is eliminated.