O72 track & Lionel No. 450 signal bridge wiring diagram.

I let the track tell me, not forcing it to go wide, nor pushing it inward. I relax it and let it take its shape. If I wanted the curve wider, I'd inserted a piece of straight-track. Other than that, I have never measured the diameter, not inside nor outside, Jim.

In this photo is an example. That is my outermost mainline track. Its curved track, at each end of this curve, the widest of the entire layout, is compose of 0-72s with straight track inserted in the middle to allow for the width apparent here..

FrankM

Thank-you MOONSON that will help considerably.  Cheers Jim

I think Lionel is measured at the center rail.  John in Lansing, ILL

Thanks RATTLER21 & cheers Jim

Here is a topic on various methods to wire the 450: https://ogrforum.com/...-wiring-for-2-trains

Here are the 1954 wiring instructions:

And yet another method: https://ogrforum.com/...sts-of-an-022-switch

JD

trainnut56 posted:

...should Lionel 072 be 072 on the inside or the outside?

O72 is 35.88" radius measured to the center rail.

  Interesting. So 0-27 is the only track to measure to the outside? I thought all Lionel track was measured to the outside rail, but never checked other than 0-27...which I think is closer to 27" to the tie edges

 Because it's easy to "oval" a circle sligbtly, The best way to check a track is build a circle and measure across the  diameter twice at 90°s (or more angles) then average those measurements.

O27 is 12.37" center rail radius, "O" is 14.14" radius, or about "O-30.5" if you measure the over-the-ties diameter. There really isn't much of a standard.