Curve Radius

good write up here

http://www.mthtrains.com/news/249

and did a google search. "for o gauge curves".

https://www.google.com/#sclient=psy-ab&hl=en&source=hp&q=o+gauge+curves&pbx=1&oq=o+guage+cur&aq=3bs&aqi=g-s2g-ms1g-bs1&aql=1&gs_sm=c&gs_upl=1405l14160l0l17714l25l17l8l0l0l0l573l2988l1.12.2.0.1.1l25l0&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=3b6976d17058900d&biw=1152&bih=574

Track descriptions that have the zero in front, like 027, 054, 072, etc. are diameters. That's the "width" of a full circle. The easy way to remember this is that the zero looks like a circle.  A curved piece of track described as 072 will create a circle of track 72" across, if extended all the way around.

Scale folks refer to radius, and the radius of a circle is half-way across the diameter.  They say 36" radius, 48" radius, etc.

So, a curved track called 072 is a 36" radius curve. (36 is half of 72)

For the most part it depends what your modelling,typically, a 48" radius  would be for a 2-rail o guage locomotive, an o-48 would be for a 3- rail o guage locomotive. Manufacturers like MTH that offer similar locomotives for 2 or 3 rail, usually give the minimum curve description for both track types.

Gentlemen Thank You very much. Mr Bloom I think that is the easiest and best way to remember the difference. Thanks again every one.

Hey how did this post get so wide

apparently when I posted the google link the hoop-la program did not keep the format.

I think the confusion comes in because HO and N all talk in radius, not diameter.