The Radius of Ophir's Loop?

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Well-Known Member
That was most helpful Willie! The guy's table was not helpful, as it is for the Outdoor scales: 1:20.32, 1:22.5, 1:24, 1:29 and 1:32. (It's interesting that they can get so many scales from a Track Gauge of 1.722 inches which is; or, was the original G scale). So, I needed to use his simplified method of determining Ophir Loops radius, which per what he stated, had a degree of curvature of 24. He stated that I should divide 5729.65 feet, which is the degree of curvature for 1 degree, by the 24 degree curvature of Ophir Loop, So, 5729.65 feet divided by 24 equals 2.74 feet; or, 33 inches. I have to assume that his 24 degrees of curvature for the Loop is correct as I have no way of knowing otherwise.

I have used Google Earth to get a Ball Park radius for the Durango and Silverton's radius at the turn around wye at Silverton, of around 300 feet and the tightest radius at the "Highline", to be somewhere around 280 feet; or, so.

Thanks Willie for that website!
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Well-Known Member
That is the length of the curve that will give 1 degree of curvature. Check out Willie's link, it will tell you there!
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Staff member
It doesn't matter to most model railroaders, but there are actually two ways to define the degree of curvature.

One is Chord definition, which is what railroads use. It uses a 100 foot chord to determine the angle. That's the one referenced in the formulas above.

The other is Arc definition, which measures 100 feet along the arc of the curve to determine the angle.

For gentle curves, the answer is nearly the same. On tight radius curves, they vary by a fairly significant amount.

If you wish to geek out on it, you can read more here:

If you ever need to hire a railroad surveyor, ask them this "Do you know the difference between chord definition and arc definition of a curve?" If they say no, look elsewhere. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to - An online railroad bookstore featuring a curated selection of new and used railroad books. Railroad pictorials, railroad history, steam locomotives, passenger trains, modern railroading. Hundreds of titles available, most at discount prices! We also have a video and children's book section. - An online model railroad bookstore featuring a curated selection of new and used books. Layout design, track plans, scenery and structure building, wiring, DCC, Tinplate, Toy Trains, Price Guides and more.