Understanding track spacing on curves

Correct, you can't truly make those two curves concentric safely.  I will guarantee that with 3.6" c-to-c on the curves that you will have problems with anything that has a significant overhang.  For instance, on O72 curves, my Vision Line Big Boy hangs out 3" from the track centerline.  For reasons I don't fully understand, the MTH Premier Big Boy needs more than that, about 3.25" from the centerline.  Either of those would contact even small rolling stock on the outside rail, the overhang would be right up to the inside rail on the outer track!

@gunrunnerjohn posted:

Correct, you can't truly make those two curves concentric safely.  I will guarantee that with 3.6" c-to-c on the curves that you will have problems with anything that has a significant overhang.  For instance, on O72 curves, my Vision Line Big Boy hangs out 3" from the track centerline.  For reasons I don't fully understand, the MTH Premier Big Boy needs more than that, about 3.25" from the centerline.  Either of those would contact even small rolling stock on the outside rail, the overhang would be right up to the inside rail on the outer track!

What do you suggest then? Going to the next step up with gargraves which is 89" or going down to O63?

I have seen many people on this forum say they use O72 and O80 on their layouts- so how are they getting away with it?

We use 4 inch spacing almost everywhere.  In yards...straight sections 3.5" works. 

Many people ask this question, and it is next to impossible to answer.  The correct answer is it depends on the sharpness of your curves and the length of your longest 2 pieces of equipment.

We use curves ranging from 72 to 96 diameter.  In places where there are parallel curves: 96 and 89--pictured below.  That leaves a shade under 4 inches between lines.  No issues.  Our longest 2 pieces of equipment: 21 inches.  No sideswipes!

My suggestion is to physically test prior to actual securing the track in place.

If you're willing to have symmetry but not perfect concentricity, just insert four short lengths (say four or five inches) of straight track into the outer O-80 circle every 90-degrees apart. That will move the outer track further away from the O-72 circle. Try it and see if you think it's satisfactory.

MELGAR

so take any car with a large overhang like a large auto carrier or container car or an engine.

place a felt pen at the front corner of the car so that the pen touches the surface. Move the car by hand to scribe a curved line on the surface.  repeat by holding the pen at the midpoint of the car.

do the same for each curve inside and outside. the scribed curves show the potential interference lines between curves.

relocate curve track and repeat until no side-by-side inference lines touch.

When the first RailKing BigBoy came out, I determined that 5.5" was the minimum track spacing for small tinplate curves I measured it on (O31, O42 and O54).  My club's O72 modules have 4.25" centers on straights but our curves are not concentric.  We use straight track to offset the start of the curve to allow additional spacing.  Check out the photo Steve posted here.

We also have wide curve modules with O120 outer diameter that maintain the 4.25 centers throughout the curve.  We often use these modules as S-curves and do not have clearance problems on them.

@John C. posted:

We use 4 inch spacing almost everywhere.  In yards...straight sections 3.5" works.

Many people ask this question, and it is next to impossible to answer.  The correct answer is it depends on the sharpness of your curves and the length of your longest 2 pieces of equipment.

We use curves ranging from 72 to 96 diameter.  In places where there are parallel curves: 96 and 89--pictured below.  That leaves a shade under 4 inches between lines.  No issues.  Our longest 2 pieces of equipment: 21 inches.  No sideswipes!

My suggestion is to physically test prior to actual securing the track in place.

I did test before laying the track!  There's no way I could live with 4" spacing, I have a bunch of articulated steam that would be taking out anything on the next track with that spacing.  On our club layout we had two tracks with 4.5" spacing, the outer track was O90, the inner track was O81.  My Vision Line Big Boy on the inside track sideswiped a 21" passenger train and took a bunch of cars off the rails.

I don't know what kind of equipment you run, but any scale articulated steam would seem to be a risk there.

There is no perfect answer because no matter what spacing is stated someone can always come up with a counter argument using some combination of unique engines and cars. (e.g. the MTH Coors engine was especially wide and some engines/car may have tremendous overhang). I think we all try to design to a 99% solution; not perfect but a reasonable tradeoff given the cars and engines we expect to run and the space restrictions we all have.

That all said, years ago I standardized on a minimum track separation of 4.5" for 0-72, 0-63 and 0-56 concentric curves (with 3 1/2" on straights). I don't recall ever having a problem in normal day-to-day operation since I am not running long cars or long engines on the smaller diameter tracks.

@MELGAR posted:

If you're willing to have symmetry but not perfect concentricity, just insert four short lengths (say four or five inches) of straight track into the outer O-80 circle every 90-degrees apart. That will move the outer track further away from the O-72 circle. Try it and see if you think it's satisfactory.

MELGAR

Thanks for suggestion, I added a straight track section on the outside curve. This seems to fix the issue.

It allows for more than enough spacing - about 5" between tracks. As others have said there are some edge cases. I run mostly steam era but want room to expand into large locos one day such as the MTH premier big boy.

@Bruce Brown posted:

There is no perfect answer because no matter what spacing is stated someone can always come up with a counter argument using some combination of unique engines and cars. (e.g. the MTH Coors engine was especially wide and some engines/car may have tremendous overhang). I think we all try to design to a 99% solution; not perfect but a reasonable tradeoff given the cars and engines we expect to run and the space restrictions we all have.

Bruce nailed it, you need to decide what limitations you're willing to live with.  FWIW, I forgot about the Coors locomotive, it won't go into my main 10-track yard because it hits the ground throws on the switches.

@gunrunnerjohn posted:

Bruce nailed it, you need to decide what limitations you're willing to live with.  FWIW, I forgot about the Coors locomotive, it won't go into my main 10-track yard because it hits the ground throws on the switches.

I decided to give more spacing than needed, at least 4.5-5" with some places with more spacing  I guess you never know and its better to do it now than later.

I started redoing the yard for more spacing but dont know if thats really necessary in a yard situation. I am using Ross #6 switches.

The Austin Tinplate Trackers track spacing is 4 1/4" between each of our 4 mainlines. Some modules us the 5th track position so we have all 5 tracks on our corners and our lift bridge module. This allows us to be more flexible in our layout design. We also have a pass through yard that must be entered via tracks 123 and 5.

Attached is the track plan for our 5 ft. corners showing track radii and spacing. We used K-Line shadow rail / super snap track. We designed 6 ft. corners as well but our layout geometry would have forced us to build extra 2 ft. modules so we went with the 5ft. corners. Since building these we have not had any issues with trains clipping each other. Those in the club with 21" plus cars and articulated engines run on tracks 1 & 2.

We also have 4 45 degree corners that made a half circle. Two of them together make an 8 ft. square 90 degree corner.  I cannot seem to find the diagrams on those corners but tracks 1 & 2 are extended 120's. They are extended by having straight sections before going into the curve. Track 3 is straight 120's. Track 4 is an extended 96 by way of a section of 120 in the middle. Track 5 is all 96's. These modules can also be reversed and create large sweeping 6 curves that all large engines and cars can negotiate with hitting each other.

Hope this helps.

FWIW, my frieght yard tracks are spaced at 3.5", no reason to space them wider once everything is straight with curves out of the picture.

I also did 3½" spacing on my yard tracks, with greater spacing in their curved leads.

@KarlDL posted:

I also did 3½" spacing on my yard tracks, with greater spacing in their curved leads.

I actually didn't worry about the spacing of the curved leads much.  Since I don't plan on a lot of multiple-train traffic at one time in and out of the yard, I couldn't see it being an issue.

Glad that no one 'attacked' yardtrain about this being a really big subject.  There is info archived about this going back a decade or more at least, probably thousands of comments, and sometimes it is easier to just ask the question again and get great answers as have been provided here.  I've stepped on a couple landmine questions that set some folks off at times.

Ross makes 084 sectional which would allow you to have concentric curves with your 072 inner line and keep 6" spacing.

@gunrunnerjohn posted:

FWIW, my frieght yard tracks are spaced at 3.5", no reason to space them wider once everything is straight with curves out of the picture.

Thanks for the photo, one issue I ran into was the actual distances between the tracks in the yard. With Ross #6 switches it only gives about 3.21".  So I would need to add little straight spaces in between switches. Is there a way to avoid this?

@yardtrain posted:

Thanks for the photo, one issue I ran into was the actual distances between the tracks in the yard. With Ross #6 switches it only gives about 3.21".  So I would need to add little straight spaces in between switches. Is there a way to avoid this?

Ross has “make-up” tracks that set the next yard track at 3.5”, 4”, or 4.5” for multiple angles. Look for model numbers TR435 or TR445 or something like that.

@rplst8 posted:

Ross has “make-up” tracks that set the next yard track at 3.5”, 4”, or 4.5” for multiple angles. Look for model numbers TR435 or TR445 or something like that.

I tried what you suggested but the make up tracks are curved and not straight tracks so I was not sure where they go. I was able to use a 3" Ross straight track pieces. Here is the current process on the layout trackplan after "fixing" the yard with proper spacing adding a new spur track on the inside track. I still have some tweaks to make

All good advice.

A couple more clearance thoughts...

1) While it's true that articulated locos will usually dictate the most problem on parallel curves with their swing to the outside of the curve, long wheel base cars...e.g., 21" passenger cars...will contribute to the problem with their overhang to the inside of a curve...especially the shaper curves common to O3R.  Of course, when they're both traversing parallel curves, it's even more a recipe for disaster.  Something to consider based on your own fleet and operating possibilities.

2) At this stage of your planning, it's not too soon to consider vertical clearance issues!  I thought my several domed passenger cars would be the criteria.  I even checked caboose cupola heights.  Satisfied I built the layout, placed tunnel portals, truss bridges, etc., etc..  Only to find that my assortment of RailKing double decker cars with die cast autos wereway taller than anything else.  Too late.  Too bad.  Sold them all. 

FWIW...

KD

All good advice.

A couple more clearance thoughts...

1) While it's true that articulated locos will usually dictate the most problem on parallel curves with their swing to the outside of the curve, long wheel base cars...e.g., 21" passenger cars...will contribute to the problem with their overhang to the inside of a curve...especially the shaper curves common to O3R.  Of course, when they're both traversing parallel curves, it's even more a recipe for disaster.  Something to consider based on your own fleet and operating possibilities.

2) At this stage of your planning, it's not too soon to consider vertical clearance issues!  I thought my several domed passenger cars would be the criteria.  I even checked caboose cupola heights.  Satisfied, I built the layout, placed tunnel portals, truss bridges, etc., etc..  Only to find that my assortment of RailKing double decker cars with die cast autos were way taller than anything else.  Too late.  Too bad.  Sold them all.

FWIW...

KD

Is there an echo in here KD?

@yardtrain posted:

Thanks for the photo, one issue I ran into was the actual distances between the tracks in the yard. With Ross #6 switches it only gives about 3.21".  So I would need to add little straight spaces in between switches. Is there a way to avoid this?

I didn't do a ladder of switches like it sounds like you're doing, I had a couple of 4-way switches that I used, then a couple of switches I had left over from the build to finish off.  I didn't have enough run to have a switch ladder for the ten tracks, that would have taken a lot of real-estate.

I got to thinking on everyone's comments on track spacing. Just like the 2R use of radii and the 3R use of diameter, seems to me the same thing is happening here. With my Ross track (and I presume its the same for all mfgs) when I said 6 1/2 inch center rail to center rail, this is the same as saying 5 inches outer rail to outer rail. Of course saying 5 inch spacing really doesn't convey what is really going on. NMRA uses track centers as their references and of course radii.  Hmm, what does "between tracks" mean?

Another thing to consider is that if you run modern equipment at home  or on a club layout where others run modern equipment.  The scale 89' flats by Atlas and the 89' Auto-racks and 86' high cube boxcars by Lionel are longer than 21" passenger cars. They are closer to 24". They too will get you with height clearances too. Scale auto racks, high cube boxcar, and double stacks are tall and you will probably need 7" of clearance from the railhead.

@Texas Eagle 77 posted:

Another thing to consider is that if you run modern equipment or on a club layout where others run modern equipment is that the scale 89' flats by Atlas and the 89' Auto-racks and 86' high cube boxcars by Lionel are longer than 21" passenger cars. They are closer to 24". They too will get you with height clearances too.

Thank you for your tip. I am considering an elevated loop on this layout in the future. I am not a big fan of modern equipment, however I do own two husky stacks. The longest thing I would probably have are some passenger cars or well cars. Most likely won’t even own an auto rack but I would still would consider the possibility when planning this.

I am testing 88, 84, and 72 as my triple main on my 18.5 by 10 foot layout. I am starting with 5.5 to 6 inch center rail spacing.  I plan on screwing down the outside track first.  Using my Big Boy, Allegany and EM1 I will add the inner loops and testing before I finalize the inner loops. I will also assure spacing for the 21 inch diner cars during that process.  I will also need to determine the location of the steel tread dowels I will need to support the 2nd level.  As others have said, the spacing is dependent upon track geometry and type of engines and rolling stock you plan to run on the layout.  Start with an assumption that either 4.5 or 5.4 inches will work and adjust accordingly.

@gunrunnerjohn posted:

FWIW, my frieght yard tracks are spaced at 3.5", no reason to space them wider once everything is straight with curves out of the picture.

John, are those track markers on the fall wall hooked up to resistors and diodes for actuators to align the switches? Well it seems you have the rest of it wired pretty nicely .

I like the use of a Y switch splitting off into two into the storage area. Is the switch on the left side a RH #6?

Thanks John.

Paul

@Railrunnin posted:

John, are those track markers on the fall wall hooked up to resistors and diodes for actuators to align the switches? Well it seems you have the rest of it wired pretty nicely .

I like the use of a Y switch splitting off into two into the storage area. Is the switch on the left side a RH #6?

Thanks John.

Paul

I wish it was automated.   Actually, all the switches on the entry to the yard are manual with ground throws, no automation.

This is the whole yard entry.  The switch at the extreme right is off the mainline, then I used a Ross RH 100 switch, two Ross 4-way yard switches, and two Ross RH #6 switches on the bottom of the picture.  I wanted to get all the switching done before I got into the yard so I had those tracks for useful storage.  Sticking some of the switches on the lift bridge worked out, that was never going to be a place to park anything anyway.

Nice John, I like that your design has to some extent built in yard leads to minimize fouling the main.

Paul

@gunrunnerjohn posted:

"I did test before laying the track!  There's no way I could live with 4" spacing, I have a bunch of articulated steam that would be taking out anything on the next track with that spacing.  On our club layout we had two tracks with 4.5" spacing, the outer track was O90, the inner track was O81.  My Vision Line Big Boy on the inside track sideswiped a 21" passenger train and took a bunch of cars off the rails."

The UP articulateds seem to have the most overhang of all, they take out signals, lineside structures, etc., so we banished them! 😉

@BobbyD I was hoping my 2-10-10-2 had the greatest measured overhang but I wonder if the Vision Line Big Boys are worse.

I don't believe GRJ uses his yard much for anything other than storing "whole trains."  Otherwise, he would find those "built-in" yard leads wholly inadequate.  The rule of thumb for yard leads is to make them as long as your longest yard track.  Of course, we as modelers often bend those rules of thumb, but we should try to come as close as space permits.

Chuck

@BillYo414 posted:

@BobbyD I was hoping my 2-10-10-2 had the greatest measured overhang but I wonder if the Vision Line Big Boys are worse.

The VL-BB has a 3" overhang from the track centerline on O72 curves.  The MTH Premier BB has 3.25" overhang, don't know why it is more than the VL-BB.

@PRR1950 posted:

I don't believe GRJ uses his yard much for anything other than storing "whole trains."  Otherwise, he would find those "built-in" yard leads wholly inadequate.  The rule of thumb for yard leads is to make them as long as your longest yard track.  Of course, we as modelers often bend those rules of thumb, but we should try to come as close as space permits.

I can move a few cars around on the leads, but you are correct, they should be longer.  However, one has to live within the limitations of the space available.

@BobbyD posted:

The UP articulateds seem to have the most overhang of all, they take out signals, lineside structures, etc., so we banished them! 😉

That ain't happening here! I confess, the first run of my VL-BB did clear out some trackside scenery at our club, but we adjusted.

Besides, there are others that are major offenders, the Y6b comes to mind, not to mention the C&O Coal Turbine.  Those are just a couple of them...

@gunrunnerjohn posted:

The VL-BB has a 3" overhang from the track centerline on O72 curves.  The MTH Premier BB has 3.25" overhang, don't know why it is more than the VL-BB.

I'll have to measure when I get home. Thank you!

@gunrunnerjohn posted:

That ain't happening here! I confess, the first run of my VL-BB did clear out some trackside scenery at our club, but we adjusted.

Besides, there are others that are major offenders, the Y6b comes to mind, not to mention the C&O Coal Turbine.  Those are just a couple of them...

Ha! I can picture the "clearing out" John. 😁

IIRC the Y6b has tapered running boards which provides a little more clearance than the straight ones. Been awhile since one was here. Thanks for the tip on the C&O Turbine, have been pondering one.

Always nice to see everyone's solutions to a common problem.

I'm sure there's a host of other "problem" locomotives, probably even some on my shelves.   I'm thinking maybe the Centipedes might be an issue as well...