Clearance

In all likelihood, no. You'll have "underhang" on the outside and "overhang" on the inside that will likely lead to equipment making contact. On those curve sizes, you'll need at least 5"-5.5" of clearance between the curves.

Chooch,

To get those two (Ross) curves to line up symmetrically, I had to use a 4" center rail to center rail spacing. (diff. in radii 072-064=8/2=4) I estimated the car bodies at 2" x 19".  If those dimensions are correct, there should be 5/8" to 3/4" clearance at the apex.

A big steam engine pilot would be another story. It's close enough you should try an actual mock up.

I thought a visual may help to see that's it's clooosse!

Measured some years ago.......

My Challenger's rear cab roof corner and front running board corner both had a 2-1/8"outer reach from center rail when passing in an 072 curve on an inner main track. For a 20"[80'] passenger car 1" inner curve overhang from the car center in an adjoining 084 on an outer main.  I was measuring to locate an 084 outer curve on the dual 072/084 mains and decided on 6" on center spacing--as Matt noted above long equipment passing in curves is the key issue that needs focus. In my case I ran passenger trains on the outer mainline and freight on the inner.

I was using 100% Gargraves flextrack which makes it easy to select the curve spacing at any desired curve arc.

 Thanks to all for your input. I saw a set of MTH Premiere cars at a good price, and began to think about it, but I had my reservations given their length, and that's why I went with this post.

   My last layout was with Fastrack 060/072 and it was a no brainer. I would love to go with 072/080, but the real estate is an issue.

    Moon man, that was a fantastic graphic! What program did you use to create it?

   Dewey, I had seen a demonstration with a Big Boy, and it too, had quite a large overhang. Being unable to to go with an 072 minimum layout I have to limit myself to 054 and smaller equipment.

Laid off sick, I have actually been working on a layoutI had first seen on the thread about your layout. I believe it was designed by Obsidian, but as stated above the real estate issue forced me to change to a smaller track size. In any case the room will not be started until the fall at the earliest. I may be able to squeeze in a couple of extra feet.

Once again thanks for all of your input. This forum is the best! Rich

Chooch,

I used SCARM. Ross library to lay the track, figures to create the car shapes to size, measure tool to check distances.

It's freeware, still in beta, with the MTH library still needing refinement.

An O scale car is typically 10 scale feet wide or 2.5" as opposed to 2". In 3-rail, many passenger cars use offset-bolster trucks which cause the car to swing inward on curves This cuts the clearance available for steam locomotive pilots.

NMRA recommendations for tight curves -- 36" Radius/O-72 is five inches. So if O-72 is the widest you can use, you probably want to cut down the inside curve to O-62 for concentric curves or set the inside curve back by an additional inch to achieve the same result.

Thanks Matt, I did check the MTH website, and they describe the cars as 2 7/16" wide so I think it would not work out too good either. Oh well back to the drawing board. 

Speaking of drawing boards, Thanks again Moonman I'll have to get back to the Scarm tutorial and figure out how to do this. Nothing like a visual depiction to have it all come into focus. Thanks again. Rich

Here's an example of what I was talking about. There are ways to achieve this where you can have the track tight in straights and widen them for the curves if you have the distance to pull it off. Prototype railroads increase separation as required for clearance for platforms, curves, signals, etc.

Here's an example of clearance between a large steam locomotive and 80-foot (20-inch) passenger cars on the above configurations

.

Thank you Matt, another great visual, that clearly make the adjustment a matter of inches rather than the feet that would be required by upsizing all of the track to 072/080. Which by the way I would still like to do if I can make it work. Even so I get how to change the center rail spacing in the curve no matter what size track is in play. 

You guys are great. Rich