Editing Tractive effort (section)

====Values and comparisons for steam locomotives====

Tractive effort is the figure often quoted when comparing the powers of steam locomotives, but is misleading because tractive effort shows the ability to start a train, not the ability to haul it. Possibly the highest tractive effort ever claimed was for the [[Virginian Railway]]'s [[2-8-8-8-4]] triplex locomotive, which in [[Expansive working|simple expansion]] mode had a calculated starting T.E. of 199,560&nbsp;lbf (887.7&nbsp;kN)&mdash;but the boiler could not produce enough steam to haul at speeds over 5&nbsp;mph (8&nbsp;km/h).

Of more successful steam locomotives, those with the highest rated starting tractive effort were the Virginian Railway AE-class [[2-10-10-2]]s, at 176,000&nbsp;lbf (783&nbsp;kN) in simple-expansion mode (or 162,200&nbsp;lb if calculated by the usual formula). The [[Union Pacific]] [[Union Pacific Big Boy|Big Boys]] had a starting T.E. of 135,375&nbsp;lbf (602&nbsp;kN); the [[Norfolk & Western]]'s Y5, Y6, Y6a, and Y6b class  [[2-8-8-2]]s had a starting T.E. of 152,206&nbsp;lbf (677&nbsp;kN) in simple expansion mode (later modified to 170,000&nbsp;lbf (756&nbsp;kN), claim some enthusiasts); and the [[Pennsylvania Railroad]]'s freight [[Duplex (locomotive)|duplex]] [[PRR Q2|Q2]] attained 114,860&nbsp;lbf (510.9&nbsp;kN, including booster)&mdash;the highest for a rigid-framed locomotive. Later two-cylinder passenger locomotives were generally 40,000 to 80,000&nbsp;lbf (170 to 350&nbsp;kN) of T.E.