Smallest prototypical curve in HO?

[nachoman]

I remember investigating this a few years ago after looking at some industrial trackage that I thought had very sharp curves. After looking at the area on google earth, I learned the actual radius was something like 300 feet. That comes out to be about 42 inches in ho scale. So, I assume the sharpest prototypical scale curve would be about 40 inches in HO.

The Uintah railway was 3' narrow gauge, and had some of the sharpest curves in the USA. I remember calculating they would scale out to be about 14-15 inches in ho scale. Remember, this was narrow gauge with specially modified locomotives and cars. They used shays and articulated locomotives only on that part of the line. I suspect some logging lines had equally sharp curves, but these were special cases.

Nobody has prototypical curves on their layout. The best you can to is use the widest you have room for, and try to hide the curve so that you can't see the whole thing at once. I am using 18" for both standard and narrow gauge because that is all I have room for. I am trying to make the sharp curves less noticeable by hiding parts of them inside tunnels.