A Deflected Tire/Rolling Resistance computer model to simulate free-rolling of a belted radial automobile tire against a flat surface is reviewed. The contact conditions are then extended to include rolling against a test wheel, and the effects of load, deflection, inflation pressure, and test-wheel curvature are investigated. The analyses are restricted to isothermal at 25°C. Both the tire force and their contribution to rolling are examined. The investigation with an analysis of free-rolling twin-rolls, predicting gross of flat-surface and conventional test-wheel results.