The following is an excerpt from The Missing Conversation Vol. 03, coming Jan. 1, 2013.

As John Armstrong notes in his classic book: The Railroad-What It Is, What It Does, it is futile to argue which was more important, a track system of rails, flanged wheels or the concept of coupling multiple cars together to form a train. All three taken together make up the most significant system of technology in the history of transportation to date: applying the heat energy output of a machine to transcend the capacity of animal power in moving cargo.

Modern 2 wear wheel

A prototype wheel looks deceptively simple at first glance, yet it is anything but. Full size train wheels have a number of functions to perform, with millions of dollars of freight and many lives riding on the outcome. Railroad wheels and track are a complex, integrated system that is carefully monitored and maintained for the safety of all concerned. As we’ll see, standards are critically important.

The beginning
The earliest railroad wheels were little more than modified wagon wheels that were sufficient to carry the lightweight railroad cars of the day. Although spoked wheel designs in both wood and metal were quite common, they soon proved unsuitable and were replaced by wheels having a disk design, typically of cast iron, which was easily worked by the metal smiths of the era. These designs evolved into the wheels we know today.

Cast iron tends toward brittleness and foundry men discovered that an extremely hard chill developed in the iron if it was poured next to another iron surface. This chilled area, as deep as an inch, could not be machined and was typically avoided. However, it proved ideal for the wear surface on freight car wheels. Therefore the rim and flange were poured as a unit against an iron ring, leaving the interior and hub areas soft and machinable.

Other considerations
You would think things like wheel diameter, tire width and flange depth appear straightforward enough, yet such was not the case initially.

Take the diameter for example. Larger wheels provided a better ride but added to the dead weight of the car. They were more expensive too, an important consideration given the ultimate number of wheels required by any line.

From what is known, a diameter of 36 inches appears to have been an early standard for freight cars. However, roads like the B&O used smaller 30 inch wheels on certain cars in the 1830s progressing in size to 31 inches, even though a compromise of diameter of 33 inches was widely accepted in America by the 1840s.

Gauging the impact of interchange
Early railroads were essentially closed systems. The trains of one line typically didn’t travel on competing lines and passengers and freight were manually transferred at end points or junctions. As rail travel and shipping of freight became more widespread, this cumbersome process began to fall apart. With manual transloading being horribly inefficient, the superiority of having cars able to travel freely from point to point soon became clear. Yet there was a huge problem looming: track gauge was anything but universal.

The interchange of freight cars among competing rail lines was unprecedented in American business history. It worked because everybody benefitted, either by increased efficiency, lower costs or both. The fly in the ointment was the wide variety of track gauges used in the United States at this time. Driven by local political interests, hubris among the “empire builders”, greediness in keeping traffic confined to their system or just an urge to be different, track gauge standards were all over the place. Pioneered by brothers George and Robert Stephenson, the Stephenson gauge of 4’ 8.5” was commonly used, accounting for over 50 percent of track miles in 1861, with the 4’10” gauge common in the states of Ohio and New Jersey only accounting for 9.9 percent. In the American South, five feet was the common standard comprising 21.9 percent of total miles of track, while the Erie Railroad’s famously broad gauge of six feet only represented a mere 5.3 percent.

Think that’s wide? A line in Missouri used 6’ 6” as their gauge for reasons no one understood. Rail lines in between these extremes used a gauge of 4’9” in an attempt to compromise the differences between the Stephenson gauge and 4’ 10”. Given the extent of trackage laid, compromise solutions to the problems of interchange abounded. Some were more laughable than others.

One stop-gap idea widely adopted for a time was an extra wide wheel tread that could traverse tracks laid to 4’-8.5” up to 4’10”. This proved to be ill-conceived at best because the running qualities of these wheels were horrible, due to the fact they didn’t conform to either gauge. By necessity the wheel flanges had to be gauged to the narrowest track leaving a lot of side-to-side slop on the wider gauges. Cars so equipped could only be moved at slow speeds and, while freight might withstand some jostling around, passengers were less tolerant. Suffice to say that railroad men hated these things.

Other schemes such as exchanging trucks, multi-gauged track composed of three and, in one case, four rails were all tried but the only solution that was going to work efficiently was to adopt a standard track gauge dimension. With miles of track already laid many lines were resistant to regauging their track, yet the handwriting was on the wall and all lines eventually adopted the Standard Gauge of 4’ 8.5”. Finally, a car could travel from one part of the country to another without the problems of delay from transloading, switching trucks and other impediments.

*** End of excerpt ***


Systems thinking
As the excerpt from TMC 03 conveys, track and wheels are an integrated system: in essence, two sides of the same coin and this relationship is just as true for our models as for the prototype. One cannot alter one part of the equation without impacting the other.

P48 wheels and flangeways

The P48 wheels and track shown above, illustrate this interdependent relationship of how the frog and guardrails work in combination with the wheel profile to guide the truck safely through the turnout. Notice in particular how the wheel is completely supported by the frog as it bridges the gap of the flangeway.This is just as critical in model form as it is on the prototype. The system is made of the width of the tire, the depth and thickness of the flange; the shape of the fillet where the flange transitions into the tire and the back-to-back distance between the inside faces of the wheels. These are complimented by the track components such as the shape of the rail head, which matches the shape of the tire, the width of the flangeways at the frog and guardrails, plus the back-to-back distance between these two.

A solution often promoted in O scale is to finally adjust the track gauge to proper dimensions but keep the existing coarse standards for wheels and flangeways. The thinking presumably is that this will allow all the existing legacy equipment built to five foot gauge to still have a place (just swap out the trucks and some drive wheels). Further claims are that it also allows modelers to decide for themselves whether to keep the legacy standards or adopt P48 for the sake of  consistency.

Here’s why I think this is a bad idea: A compromise is a compromise is a compromise. This is the situation in HO now. HO has one track gauge yet it also has multiple options for wheel specs such as the RP25, Code 88 semi-scale and P87 proto-scale.

P87 wheels and NMRA flangeways are not a system

Look closely at this image of P87 wheels on a regular HO scale Shinohara turnout. There are a multitude of problems here. Even though the track gauge is acceptable for P87, the flangeways are not. While the grossly oversized flangeways work with the out-of-scale NMRA wheels they were designed for, the P87 wheels have nothing to support or guide them through the frog. Notice the huge gap between the wheel face and guardrail on the left. Why is it so huge? Because the back-to-back dimension is vastly different between P87 and the NMRA standard. By reducing the width of the wheel tread and thickness of the flange to scale dimensions, the back-to-back distance is also widened. Do you see how interdependent all these relationships are and why changing just one aspect affects all the others?

Notice further how the wheel on the frog has fallen into the gap created by the wide flangeway, instead of being supported by the wing rail as it should be. The semi-scale Code 88 wheels that are becoming more popular in HO are not designed to this flangeway either. While they don’t drop into the gap completely, there is a noticeable bump when traversing certain brands of turnouts. Like the compromise attempt of the extra wide tires used by the prototype, such compromised solutions on our models are only marginally effective. Our models, like the prototype are made up of systems. It’s all or nothing, pick your standards and be consistent.

Why does this matter to us as modelers? I believe that fine scale modeling is the visible outcome of a journey that starts with the prototype. A modeler starts with a closer examination of the prototype and, as a result, gains a more thorough knowledge of the components and how they work together. With that knowledge comes greater clarity of how compromised many aspects of our models have become over time. From that point I believe  a decision has to be made: Accept the out-of-scale features for the compromise they are or continue the journey wherever it leads.

I understand that many folks are happy with such compromises for the simplicity of building with readily available products or the savings in time they offer. For my modeling such visual discrepancies ruin the effect I want to achieve. For me, such details matter a great deal. I believe it’s important that a model be consistent in scale from the rails to the running board, which is why I choose to follow the path wherever it leads.



  1. willbacker45

    Love the excerpt! Cant wait to read TMC3! I dont think that there are any compromises that ever turn out to be anything but harmful, this is why they are a compromise. I think that no matter what scale you model or what gauge there are certain standards that are in place for a reason. Certain things are meant to work together! Although I am not modeling P48 I still will build to the exact specs that O scale requires. This way everything will work as it is meant to.

  2. mike

    “Certain things are meant to work together!”

    Indeed they are Will. As your studies no doubt prove, such relationships are critical. Our models don’t have the exact same issues as the prototype however, certain aspects are universal regardless of the size. Thanks for writing in.