When we take up passenger service we come to a much more difficult and interesting part of the subject, for here we must consider it in all its bearings, and meet the complications that varying conditions of place and service impose.  In consequence, I do not believe we can recommend one diameter for all passenger car wheels although such a state of simplicity would be most desirable.  For instance, in a sandy country where competition is active, and consequently speed is high and maintained for a length of time without interruption, I would scarcely hesitate to recommend the use of cast iron for car wheels, because steel will wear out so rapidly in such a place that its use will be unsatisfactory.  If then cast iron is used, we will find that we cannot make with it as large a wheel as we may determine is desirable when steel is used.  And just to follow this line out to its close I will state here that we find that 36 in. seems to be the maximum satisfactory diameter for cast iron wheels, because this size does not give greater mileage than 33 in., costs more per 1,000 miles run, and seems to be nearer the limit for good foundry results.  On the other hand, a 36 in. wheel rides well and gives immunity from hot boxes—­a most fruitful source of annoyance in sandy districts.  It is also easily applicable where all modern appliances under the car are found, including good brake rigging.  In all passenger service, then, I would recommend 36 in. as the best diameter for cast iron wheels.

Next taking up steel wheels, a great deal might be said about the different makes and patterns, but as the diameter of wheels of this kind is not limited practically to any extent by the methods of manufacture, except as to the fastening of the wheel and tire together, we will note this point only.  Tires might be so deeply cut into for the introduction of a retaining ring that a small wheel would be unduly weakened after a few turnings.

On the other hand, when centers and tires are held together by springing the former into the latter under pressure, it is possible that a tire of larger diameter might be overstrained.  But allowing that the method of manufacture does not limit the diameter of a steel wheel as it does a cast iron one, the claim that the larger diameter is the best is open to debate at least, and, I believe, is proved to the contrary on several accounts.  It is argued that increasing the diameter of a wheel increases its total mileage in proportion, or even more.  Whether this be so or not, there are two other very objectionable features that come with an increase in diameter—­the wheel becomes more costly and weighs more, without giving in all cases a proportionate return.  We have to do more work in starting and stopping, and in lifting the large wheel over the hills, and when the diameter exceeds a certain figure we have to pay more per 1,000 miles run.  I am very firmly convinced that the matter of dead weight should receive more attention than it does, with a view to reducing it.  The weight of six pairs of 42 in. wheels and axles alone is 15,000 to 16,000 lb.