The County Class used the same cylinders and motion as Churchward's six-coupled locomotives and required the same mass to counterbalance the reciprocating parts of the motion. However the weight required had to be divided between four driving wheels rather than six. The heavier balance weights produced a high level of wheel hammer blow; at 6 revolutions per second the hammer blow was 8 tons, compared with the 3.6 tons of the inside-cylindered City Class and the 6.4 tons of the six-coupled Saint Class. The left hand trailing axleboxes often developed hammering, which was caused by the amount of counterbalancing used.