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Scale and Gauge Tips
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Many people have wondered what the "G" in "G Scale" really means. Some say it stands for Garden. Other say is stands for Gross (German for large). However, I suspect that "Goofy" is the real source phrase because it adequately describes the state of "G Scale."
Unlike the relative state of sanity that exists in other common scales, "G Scale" or "Large Scale" is not a scale at all but a range of different scales where the models all run on the same track.
HO scale is 1:87. This was derived from standard gauge prototypes that run on 16.5 mm track. The track scales to 1:87 so the models are scaled to 1:87 also. If a narrow gauge prototype is modeled, the model is still 1:87 scale and runs on track with a gauge less than 16.5 mm. Narrow gauge models are physically smaller because the narrow gauge prototypes were smaller.
Scale is the ratio of size of the model to the size of the prototype. Gauge is the distance between the rails. If all is well, gauge scales in the same ratio as the size of the model. However, this is not always so.
In the large scale world, the whole concept is turned upside down. Everything runs on 45 mm gauge track and the scales of the models are "adjusted" to fit. A 3' narrow gauge model works out to 1:20.3 scale on 45 mm track. Meter gauge models are 1:22.5 on the same track. Standard gauge (4' 8-1/2" gauge) models should be 1:32, but some are scaled at 1:29 instead. 1:24 scale models should represent 42" gauge prototypes, but this scale is often used for 36" prototypes simply because scaling at 1/2" to the foot is easy.
Prototype narrow gauge equipment is physically smaller than standard gauge equipment. A narrow gauge boxcar is typically 30' to 32' long. A standard gauge boxcar might be 40' to 50' long. When these models are scaled to run on 45 mm track, the physical size of the models often work out to be nearly the same so that when the models are run together, they look about the same size.
For large scalers who are less concerned about consistent scale, this works out fine. They can lash together a consist of mismatched equipment and just run it. For modelers who care about proper scale relationships, this is sacrilege and intolerable. To each his own.
For American prototypes, there are three reasonable scales which represent most of the prototype railroads. These 1:20.3 for 3' narrow gauge models, 1:32 for standard gauge models, and 1:24 for 3' 6" narrow gauge models.
Unfortunately, the majority of the models available are at other scales than the three obvious ones. LGB is primarily 1:22.5 (due to their European meter gauge heritage). Aristo is at 1:29 (due to a fudge to make models of standard gauge prototypes "look" better when placed next to 1:22.5 scale models). Most Bachmann cars seem to be between 1:24 and 1:22.5.
There is some mass produced 1:20.3 scale equipment becoming available, particularly the Bachmann Shay, but most 1:20.3 modelers are stuck scratch building or building from wood and metal kits. There are quite a lot of detail parts available that are suitable for 1:20.3, so scratch builders don't have to build everything. One would hope that with the obvious success of the Bachmann Shay, that relatively inexpensive ready to run plastic models will become available in this scale.
There is a variety of 1:32 scale models available but most of it is finescale equipment fabricated in brass. These models are highly detailed and VERY expensive. There are some plastic models that are close to 1:32 scale. USA Trains steel box cars and some MDC cars are acceptably close. But for the most part 1:32 scale modelers must either have very deep pockets or roll their own.
1:29 scale is the defacto scale of choice for mainline standard gauge models simply because the vast majority of available relatively low cost plastic models are manufactured in that scale (Aristo and USA Trains). By measurements, most of the models are pretty self consistent in dimensions except that many of the Aristo models are too tall (due to excessive spacing between the trucks and the carbody) and most of the USA locomotives are too low (due to small wheels). Due to the scale/gauge mismatch, the wheels are set 10% too close together.
This scale/gauge mismatch bothers some people quite a bit. However for those that run their trains out of doors, this 10% discrepancy really is a small problem compared to the "scale" of the track itself. Most of the track used outdoors is way to large to represent real rail, it is about twice as big as it should be. This is necessary to allow the track to have sufficient strength to put up with the physical abuse that it will get in outdoors service. The "scale" of typical curves is also grossly incorrect, usually by a factor of 10 or more. Prototypical curve radius for standard gauge models would be way to large to fit in an ordinary backyard. It is hard to understand why a "scale" modeler could accept 100% to 1000% scale errors in the track and be intolerant of a 10% gauge error of the equipment that runs on that track.
The large scale manufacturers will make what people will buy. Until such time as a large percentage of the Large Scale train purchasing public insist on true-to-scale models, the current state of "goofiness" will continue to exist.
Contents
The Large Scale Working Group
A working group was formed to define the scales, gauges and designations of the variants of "Large Scale." This is a copy of their report which was provided to me by Larry Rose. Be aware that there may be data translation errors in this version. I caught one, there may be more. Also I don't know if this is a final release or a draft version.
Fine Scale Dimensions
| Scale Ratio |
Scale Letter |
4-81/2 Gauge |
42 in Gauge |
Meter Gauge |
3 Foot Gauge |
30 in Gauge |
2 foot Gauge |
|---|---|---|---|---|---|---|---|
| 1:32 | #1 | 45 mm | 32 mm | 28.6 mm | 19 mm | ||
| 1:29 | A | 49.5(1) | 37.5 mm | 32 mm | 22.5 mm | ||
| 1:24 | 1/2 | 63.5 mm | 45 mm | 41 mm | 37.5 mm | 32 mm | |
| 1:22.5 | G(2) | 64 mm | 45 mm | 41 mm | 32 mm | ||
| 1:20.3 | F | 70.5 mm | 49.5 mm | 45 mm | 37.5 mm | 30 mm | |
| 1:16 | 3/4(3) | 89 mm | 64 mm | 60 mm | 45 mm | 37.5 mm | |
| 1:13.5 | M | 106 mm | 71 mm | 64 mm* | 45 mm | ||
| Appended Letter: | n3 1/2 | m | n3 | n2-1/2 | n2 |
| Notes: | (1) A Hi-Rail version of this scale is currently marketed using 45 mm gauge track. (AristoCraft) |
| (2) NEM 010 refers to this scale as II Scale | |
| (3) NEM 010 refers to this scale as III Scale | |
| * This value was corrupted in the original copy, it has been "corrected" - gws |
AAR Scale Dimensions
| Scale Ratio |
Scale Letter |
4-81/2 Gauge |
42 in Gauge |
Meter Gauge |
3 Foot Gauge |
30 in Gauge |
2 foot Gauge |
|---|---|---|---|---|---|---|---|
| 1:32 | 3/8 in | 1.76 in | 1.125 in | 0.75 in | |||
| 1:29 | 10.5 mm | 49.5 mm | 32 mm | 22.5 mm | |||
| 1:24 | 1/2 in | 2.35 in | 1.75 in | 1.5 in | |||
| 1:22.5 | 13.5 mm | 63.8 mm | 44.4 mm | 40.6 mm | |||
| 1:20.3 | 15 mm | 71 mm | 45 mm | 30 mm | |||
| 1:13.55 | 22.5 mm | 45 mm |
The following table is provided as an approximate guide for converting between inches and millimeters for the various track gauges. A more precise conversion can be done by using the conversion 1 inch = 25.4 mm.
| mm | 22.5 | 28.6 | 32 | 37.5 | 41 | 45 | 49.5 | 60 | 64 | 71 | 89 | 102 |
| inch | 7/8 | 1-1/8 | 1-1/4 | 1-1/2 | 1-5/8 | 1-3/4 | 2 | 2-3/8 | 2-1/2 | 2-3/4 | 3-1/2 | 4 |
| Signed: | |
| Stan Ames | (Working Group Chairman) |
| Marc Horovitz | (Editor, Garden Railways Magazine) |
| Glenn Joesten | (Large Scale Committee Chairman) |
| Joe Macaluso | (#1 Scale Committee Chairman) |
| Gary Raymond | (President: Gary Raymond Metal Wheels) |
| Garrett Paine | (Large Scale Modeler) |
| Russ Reinberg | (Editor, Outdoor Railroader Magazine) |
| H. Lee Riley | (Director, Product Development, Bachmann Industries) |
[ Top ]
Scales and Gauges
For reference, this is a worksheet that I developed to aid in my own understanding of scale and gauge of various model railroad scales. Any errors in this sheet are entirely my responsibility.
Model Railroad Scales and Gauges
| Name | Claimed Scale | Actual Gauge | Prototype Gauge | Scale Based on Track Dimension |
|||
|---|---|---|---|---|---|---|---|
| in | mm | mm | in | Narrow | Standard | ||
| Z | 220 | 0.256 | 6.5 | 1435.1 | 56.5 | 220.8 | |
| N | 160 | 0.354 | 9 | 1435.1 | 56.5 | 159.5 | |
| TT | 120 | 0.472 | 12 | 1435.1 | 56.5 | 119.6 | |
| HOn2.5 | 87 | 0.354 | 9 | 762 | 30 | ||
| HOn3 | 87 | 0.414 | 10.51 | 914.4 | 36 | 87 | |
| HO | 87 | 0.65 | 16.5 | 1435.1 | 56.5 | 86.98 | |
| OO | 76 | ||||||
| S | 64 | 0.875 | 22.23 | 1435.1 | 56.5 | 64.57 | |
| Proto48 | 48 | 1.177 | 29.9 | 1435.1 | 56.5 | 48 | |
| O27 | 48 | 1.25 | 31.75 | 1435.1 | 56.5 | ||
| #1 | 32 | 1.772 | 45 | 1435.1 | 56.5 | 31.89 | |
| REA | 29 | 1.772 | 45 | 1435.1 | 56.5 | ||
| 24th | 24 | 1.772 | 45 | 1066.8 | 42 | 23.7 | |
| Gn3 | 22.5 | 1.772 | 45 | 1000 | 39.37 | 22.2 | |
| 20.3 | 20.3 | 1.772 | 45 | 914.4 | 36 | 20.3 | |
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A New Proposal
"Chili" John Pritchard has proposed an insanely simple method of designating scale that is so easy to understand that it is not clear why it hasn't been implemented already. The original thought was to use the letter "G" followed by an indication of scale. "G" is pretty universally associated with Large Scale. However, some manufacturers were sensitive to the use of "G" because it also is associated with a particular brand name. Therefore, the letters "LS" for Large Scale are proposed followed by a number indicating scale.
A New Proposal
| Scale | NMRA Designation |
Proposed Long Form |
Proposed Shorter Form |
Proposed Short Form |
|---|---|---|---|---|
| 1:20.3 | F | LS-1:20.3 | LS120 | LS20 |
| 1:22.5 | G | LS-1:22.5 | LS122 | LS22 |
| 1:24 | H | LS-1:24 | LS124 | LS24 |
| 1:29 | X | LS-1:29 | LS129 | LS29 |
| 1:32 | #1 | LS-1:32 | LS132 | LS32 |
My personal preference is for the Short Form as it seems to have fewest redundant symbols in it, however any of these designations are clearly superior to the NMRA alphabet soup.
[ Top ]
This page has been accessed times since 30 Oct 1999.
© 1998-2000 George Schreyer
Created Mar 22, 1998
Last Updated Oct 22, 2000
