4-8-4+4-8-4 classes of 4-8-4+4-8-4 steam locomotives across the globe, all of which were constructed by Beyer, Peacock and Company, the owners of the Garratt patent. The predecessor 4-8-2+2-8-4 Double Mountain was probably the optimal Garratt wheel arrangement, with the four-wheeled leading bogies and the two-wheeled trailing trucks on each engine unit ensuring stability at speed and with sixteen coupled wheels for traction. More coupled wheels would inhibit the locomotive on tight curves, while the only advantage of more non-coupled wheels, such as on the Double Northern, was to reduce the axle loading. The second Double Northern locomotive class were the AD60
2-8-8-8-8-8-2 2-8-8-8-8-8-2 Under the Whyte notation for the classification of steam locomotives, a 2-8-8-8-8-8-2 has two leading wheels, five sets of eight driving wheels, and two trailing wheels. Because of its length, such a locomotive must be an articulated locomotive. It is not longer than a normal articulated; the fourth and fifth sets of drivers are located under the tender. Other equivalent classifications are: UIC classification: 1-D-D-D-D-D-1 (also known as German classification and Italian classification) AAR classification: 1-D-D-D-D-D-1 French classification: 140+040+040+040+041 Turkish classification: 45+44+44+44+45 Swiss classification: 4/5+4/4+4/4+4/4+4/5 The equivalent UIC classification is to be refined to (1'D)DDD(D1'). The Baldwin Locomotive Works