Re: John and Dave

In addition to some of the mind-numbing physics involved, there are also a lot of intangible variables involved, such as the condition and profiles of the rails and wheels. Every engineer knows the difference between "good" and "bad" rail - heavily curve worn rail with smaller head size is "slippery" while new or freshly ground rail pulls good. New wheels with good profile and "soft" steel pull better than wheels that the profile is worn flat and the tread has become work hardened. Worst combination is worn wheels on worn light rail track. Some engines can't hardly pull themselves around under conditions like that - throw in some ice, snow, wet leaves and inoperative sanders and you ain't goin' nowhere. Its amazing what a big difference all these factors can make on how well an engine actually "pulls".