I've been looking at my old tubular Lionel brand track stored in my parent's attic and it doesn't match the Lionel O-Gauge or Lionel 027 curvature specifications seen everywhere on the Internet. After a lot of research, I finally figured out that my curves are Lionel 031, a lesser known variant that produces a radius of ~ 30" on the outer rail and ~31" to the outer edge of the crossties. (I don't make this stuff up folks -- over the many years, Lionel has concocted some interesting "radius" calculations that have stumped modelers of several generations). I wanted to mention this in case others discover as I did, that O-Gauge and 027 tubular track were not the sole Lionel curved track options. I don't know when 031 tubular track was offered (postwar? prewar? both?) I have two Lionel locomotives that are documented to not work on 027 track because of the tight curvature. Looks like I'll have to test 'em on 031 and see what happens, as I can't find any documentation for these on that radius. If they fail, I have some Super-O which will work for certain.