Those big 4-2-4s look odd to our eyes, but they were very stable and very fast, averaging 60mph, and one was recorded at 83mph down Dainton bank (one of the big 4-4-0 saddle tanks achieved 88mph in the same place with the up Plymouth mails conveying urgent despatches during the ACW). The change in wheel diameter was in answer to increasing loads and to reduce the stress on the crank axle. These regularly achieved speeds must be seen against the background of the "standard gauge lines which were barely averaging 50mph at the time and speeds of 60 were considered excessive. Indeed some of Stephenson's engines, the so called long boilers were unstable at these speeds