Model Railway Track: Code 75 or 100?

So you’ve picked a scale to model in. It would be reasonable to think that the most important part of railway modelling – i.e. the track and the stock – would be an accurate scaled down version of the real thing. Well you’d be wrong.

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OO Gauge suffers from a historical anomaly that means it’s rolling stock is actually too big for the track in runs on. In the early 20th century British model manufacturers had decided to compete with their American counterparts who had just launched O gauge. (Half of O Gauge, 3.5mm to the foot scale or 1:87). However to keep costs down they were still manufacturing models with wind up mechanisms. This method of propulsion was proving hard to fit into 1:87 scale models. The solution was to enlarge the models to 1:76 scale (or 4mm to the foot). Instead of enlarging the track with it – a costly exercise, the British manufacturers simply continued to import the American HO track and built the models’ axle width to cope accordingly. At the time, when manufacturing techniques were cruder than they are today, this inaccuracy was not so noticeable. Unfortunately the mismatch in scale sizes stuck, and is still in use by all the major companies (Hornby, Bachmann, Dapol, Heljan etc) today. The inaccuracy may still be hard to spot with the majority of models, but put a British OO Gauge model next to an American or European HO counterpart on the same track and the difference will certainly be noticeable.

So what can be done?

Some modellers do what the British manufacturers never did and properly enlarge the HO track to it’s true 1:76 scale. This is known as EM Gauge (and an even more accurate scale is P4), although you might often hear it referred to as ‘Fine Scale.’ This is a rather drastic step and almost exclusively requires scratch built track to be constructed by the modeller in question. It also requires all the wheel bases and axle widths to be altered on the models themselves to cope with the enlarged track. The results are certainly remarkable, but this is usually beyond the Novice modeller such as myself.

Track Codes: What’s the difference?

An alternative is to look at improving the rail dimensions without altering the actual gauge. You may have heard people talking about Track Codes – these are alternative varieties of off-the-shelf HO/OO Track with different rail heights. The gauge is exactly the same, but the rail height varies in an attempt to be more accurate. The track you get in any Hornby, Bachmann or Peco starter set is almost definitely Code 100 (sometimes referred to as ‘Set Track’). The ‘100’ simply means that the rail is 0.1 inches high. If this were to be scaled up along side OO Gauge rolling stock, the rail height would be almost 30% higher than it’s real life equivalent. Code 75 track (with a rail height of 0.075 inches) is far more accurate. If you scaled this up it would this time be 3% lower than it’s real life equivalent. It’s still not perfect, but it’s much closer to the mark than Set Track.

Codes 100 and 75 are the most common but there are of course other varieties: Code 83 is used to improve the accuracy of North-American-Image rail heights and Code 60 can be used on UK-Image layouts to mimic 3rd and 4th rail systems.

Do you need to worry about the difference?

Absolutely not. Many great show grade models have used Code 100 track. When ballasted properly you can still achieve a great effect, and it certainly looked good on Langstead Junction… However, Code 75 track will look that tiny bit better still. To help you make up your own mind I’ve got hold of some Code 75 track to do a comparison.

In the following picture the shallower rail height is certainly noticeable on the Code 75 track. The sleepers also look less chunky, and better spaced.

Top: Code 100 Bottom: Code 75

The rail height is really noticeable side on:


Left: Code 100 // Right: Code 75

With stock added, the Code 100 doesn’t look too bad and from this angle the difference is less noticeable:

Left: Code 100 // Right: Code 75

Left: Code 100 // Right: Code 75

The front on comparison isn’t great due to the light, but it’s just about clear that Code 100 looks a touch big from this angle although there’s not much in it.


Left: Code 100 // Right: Code 75

From above the Code 100 sleepers look too chunky, and the rails are noticeably bigger. From this angle Code 75 looks great:

Left: Code 100 // Right: Code 75

Left: Code 100 // Right: Code 75

From some angles Code 75 looks noticeably better, but form others the difference is hard to tell. On the other hand Code 100 is tougher, cheaper and curved radius’s come in pre-formed pieces (or set track to you and me), whereas Code 75 is only available in long strips of Flexi-track and can therefore be more challenging to create authentic looking curved sections.

As with most things in modelling there are pros and cons to each side of the argument. I’ve decided to use Code 75 from Peco for my new project, Woodford Wells, as the majority of the track is fairly straight and easy to shape.

If you want to read more about Track Codes I strongly recommend visiting Model Rail Workshop to read the full study and comparison. This post certainly helped me!

– Andy Carter