Minimum Radius

80".  But space is always a concern; the best I could do was 74" for my big Northerns with skinny tail beams.  I had to cheat with my articulated coach diaphragm even on that broad radius.

Yeah space is a concern as always. We are going to build a new house here in Houston and my hot-blooded Latin woman has given me a clear signal for my own large space. In my avatar you can see how I look when I win a battle.

80" is just over 13 feet for a complete turn. I think I'm going to be able to get that space. Not bragging as this has been a long time in coming. Built a complete HO layout in my 2-car garage years ago and this will be my first "O".

I assume super-elevations have to be done with hand-laying of track or can it be done with Atlas flex?

Any other inputs I'm listening.

Chuck

If space was truly not an issue??? Then dream BIG!!!

I'd go with O-100 minimum.

Real world on my 14 x 32 layout??  O-72 on my mainline and O-42 for my logging shortline.

O-72 looks OK,,,,,I too would like bigger......but OK

PS just noticed I was in 2 rail.....sorry....my world is 3 rail!!!  still go as big as you can. As I have gone from 3 rail traditional to 3rail scale......O-72 is kinds small!

I appreciate the heads-up Tom! I built a large HO layout using every bit of John Armstrong's book and am probably about 8 months away from starting any benchwork for this new project.

That being said I have learned to listen especially to those who have made mistakes... I have made my share that's for sure.

Houston is pretty barren when it comes to 2-rail layouts... I believe there is someone in Kingwood who has a nice layout?

Over the next few months I expect to ask many questions and will heed your advice about visiting other projects. Right now I'm casting dozens of hydrocal rocks and buying what flex track I can afford. My dog-eared "Track Planning for Realistic Operation" is back on my desk.

The planning sure is a fun part of it!

Thanks Tom.

Chuck

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Does this include reversing loops or strictly around the wall?

Thanks.

Chuck

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Chuck,

A minimum radius of 72" is sufficient for large engines.  They negotiate the curve well and look good also.

You can superelevate flextrack easily by placing a piece of stripwood under the outer edge of the ties.  I use 1/16" square stripwood for a noticeable superelevation but one that does not cause operational problems.

Tom is correct.  While you are waiting for your train room, see as many O scale layouts as you can to find out what you like and dislike.  Take notes of important features you want to include and avoid.

Best of luck.

Ed

You may want to figure out what you want to model before you decide on the mechanical issues like radius.    And decide on what type of operation you are aiming for.   

For example do you just want to run trains around and watch them?    Then a double track loop with large radii is good.   As mentioned 72 inch radius (O-144) is good for almost any big steam.    

But if you like scenery more, maybe you use a bit smaller radii and have the main curve back and forth along the longer axis.

Finally, if you want to operate using switchlists or car-cards or something like that, you may want to get more specific about era and type of equipment.    Most older brass smaller than mountains and northerns, all 40 and 50 ft cars, and almost all 4 -axle diesels will go around 48 inch radius.    so if you want to model 40s-50s era with that kind of equipment, you can use smaller curves and get more room for industries and sidings and operation.    I model the 40s and sometimes the early 60s and I run all that stuff.    I also easily run GGD pullmans and coaches (full-size) on 52 inch radius.    

I can't speak for more modern longer cars, but my guess is most of the newer stuff made for the 3-rail market would go around 48-52 inch radius.    The hhighly detailed museum quality brass with fully detailed under frames and brake rigging will probably balk.   

With a decent radius (72"+) reverse loops flat out steal real estate.  In John Armstrong speak, think of curves in squars.  As your ROW exceeds well over one quarter of a circle stuff gets awkward.  Unless your area is large, it would be best to have a spare room for just the reverse loops or a helix. 

The most difficult situation is when some one is buying up a bunch of large locos and 80' cars wants to builf an empire in a modest room.  It can get a little wierd.

Build with a theme that will fit the room, budget and time available.

That's it pretty much in the old nutshell.  Define your boundary conditions up front.

If you have good space for 72" radius, then by all means design for it.

I designed my layout with most curves being 72" and 68" for the mainline. When I realized what my engines and rolling stock could actually negotiate, I knocked most of the mainline down to 64" and 60" so I could have a little more tangent track. I went down to a mainline minimum of 60" and 56". I used easements where I was able.

Like others have said, what you are modeling makes a big difference. After I visited the N&W west of Bluefield, I realized there were many tight curves and steep hills greatly suited for my basement railroad.

With a good design, hills, tunnels, and dividers can carve up even a modest space to make large trains and long passenger trains work visually.

If you are running a UP 9000 across the plains somewhere, I'll be looking forward to seeing solutions to that.

I've heard this discussed over many years.  The bottom line is use the largest curves you can, because even if you don't need big curves everything looks much more realistic.  I understand that you need to compromise as well.  I'd have nothing less than 72 radius, 144 diameter curves everywhere if I could, but I don't have a gym.  Therefore my minimum are 72 diameter 36 radius curves which is tight for O scale especially if you are full-sized O stuff.

Re-read John Armstrong's book for a thoughtful discussion of the trade-offs between operation, space, aisle width, and visual appeal.  On my walk around railroad I use broad curves for visual effect in most areas and tight curves in hidden areas to pack as much prototype based operation in my available space. My minimum radius is 58" on the innermost of five hidden 40' long  staging tracks and have no issues with running scale length passenger cars and fully flanged 2-10-4's and 4-4-4-4.  Out on the visible main the curves are quite a bit larger.  Also consider that how curves are perceived is significantly influenced by how they are viewed.  Equipment viewed on curves viewed from the inside of a curve appear more prototypical that the same equipment viewed from the outside of the same radius curve.  The same is true if viewed from near eye level rather than from above.  With space at a premium even in a very large basement, (2600 sq ft)  I found it well worth while to invest in layout design CAD software to facilitate iterative design trading off the many variables factored into a track plan.

Ed Rappe

Tom,

You said," In John Armstrong speak, think of curves in quarters."  John used the term "squares" not quarters.  The side of the square is the radius plus twice the center to center track spacing suitable for that radius.  See page 52 of THE BOOK, aka Track Planning for Realistic Operation.  i can pick this book out of my collection in a heartbeat because it is the only one with such a tattered appearance.

BTW, I used squares to design my RR.  My railroad was 6 squares by 10 squares.  I could draw a rectangle 6 by 10 and doodle just about anywhere.

Ed

It is very important to have a large minimum radius, because a model railroad looks silly unless it is completely devoid of straight track. At least 96" minimum radius is a must--that way your roster of articulated steam will have minimal wheel wear From sideways friction.  

The first question to answer is what is the minimum radius possible in order for your equipment to run properly. The layout must run reliably or it won't be fun.

the second question deals with the cosmetic factor inherent--what amount of overhang can you live with and why...and I bet ten different people could come up with 10 different answers to this question....

the third question is the most relevant: what will your minimum radius requirements do toward your overall modeling goals? There will almost certainly be areas where you can go smaller on your minimum radius without causing a problem--but there will be areas where the cosmetic factor of a curve can make or break that entire scene. That's where the large radius curve is needed and wanted, not somewhere in a turnback curve where nobody can see the darned train....

Jeff C

I would recommend that you decide on what you are trying to accomplish and then it also depends on the size of your layout.  I know larger radius curves always look better as far as the curve but if for instance you are really concerned with operations, you can really lose a lot of operating area with large curves.  They look really nice but they also waste a lot of modeling space.  I have found this to be true.  Its a tough compromise but if you are using large curves in a relatively small area for O-scale, I would say anything smaller than 30 ft by 40 ft, I would really recommend laying out track and seeing how much space is eaten up by really large radius curves.  it starts to look like just a big circle to me and as a whole can be distracting.  That is just my opinion from prior experience.   Sometimes what you have on paper looks and feels a lot different when you get all your bench work build and lay your track.  I have got to that point a couple times over the years where I had to pull up and tear out what I had going because it didn't feel right in the space I had.   I think it is important to find a good balance....

bottom line - figure out what the minimum operating limits are for the equipment you are planning on using.  You can only be sure of this by laying some curves and actually running your stuff through them.  Then you can go bigger than that up to where it infringes on other goals you have.  that is how I have determined radii for layouts I have built over the years.  Works for me!

Have fun with your planning and building!

Don

As we all know the planning stages are a big part of the fun.

I wonder why Atlas 2-rail track stops at 54" radius? I can use Flex track which is fine... I assume that 54" just won't cut it and will start thinking bigger curves.

All of your inputs are appreciated and they are being listened to. Back when I built my first big HO layout in 1995 there wasn't the internet and forums you could rely on like we can today.

Lots of experts on here!

Chuck

Not sure you read all the replies.   A bunch said that 54 inch radius would work just fine with some types of equipment and might be desirable if you really want to operate.

But I would rather use flex track and be able to fit the curves to each location with a minimum overall.    

For reference, John  Armstrong, the Master, had 58" min radius on his layout, the Canadaigua Southern. As I recall, the sharpest curve was in one location only. He ran big locos, too, although I believe the largest was a Challenger-type. But, big, rigid-frame locos-2-10-2, 2-10-4- and his masterpiece, a double-Belpaire 4-8-4.

8 of the replies indicated using a curvature much larger than 54" which is why I asked why Atlas didn't go bigger.

Above are photos of my HO layout using every trick in John Armstrong's book except easements (which I will use this time).

The original question said space was not the criterion.  If you have accurate scale Northerns with narrowed tail beams, you will find nothing less than 72" will do.  When a 2-10-2 is said to go around 54" radius, that is because the cylinders, pilot beam, and tail beam have all been seriously modified.  A Challenger, properly set up with extra space between engines, can do 54".

Back when I was buying restorable doorstops, about half would come in with the inner part of the cylinder block Dremeled away, and only a thread left at the tailbeam.

Even my own locomotives have gouges in the pilot beam so the flanges will not short out. On a real railroad the wheels do not even come close, laterally.

If you do have space limitations, 2- rail locomotives and cars can be made to go around any radius that a 3- rail model can.  The problem is, you have to do some cutting.  Lionel and MTH do the cutting for you, so 2- rail their models if you need O-27.  Simple.

If you have no restrictions, go with 80", spiral easements, and 1/16" superelevation.  If you do have restrictions, change the first post?

There are no restrictions fortunately. I like the 80" you mention along with easements and superelevation.

Thanks to everyone for the help. I thought 54" would be fine but it appears that is not the case.

Chuck

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All of the recent 3rd Rail/Sunset large steam locos require at least 56" minimum radius....

Jeff C

Jeff,

I'm thinking 56" seams about right for the larger rigid wheel base engines. I don't think it is true for the articulateds. 

The recent Y6 engines get around curves in the 40"-50" range. They would get around 40" with a longer drawbar. The extended grab irons on the cab touch the tender at 40".

I'm not saying this is desireable visually but I use the tighter curves in hidden staging areas.

I'd bet they don't even test below 56" on the larger engines.

I should have specified non articulated locos. 

Jeff C

Chuck,

If space is not an issue, as others said, go big young man, go BIG! Atlas has up to O108 track, that's a 9 foot diameter circle. Every engine and passenger car would look real good on that. If that is out of the question, go at least O72. Because of space, my layout has a couple of O54's and O63's from Atlas and the rest are O72's.

Wrong forum.  Those numbers are diameters.

If watching trains run around an oval is your thing by all means go with the broadest curves you can fit in the space. 

But if you want long runs while seeing the route only once in your field of view, have multiple towns with local freight switching, and perhaps helper districts you'll probably have to fold the route one or more times down the middle of the layout room.  As discussed in John Armstrong's book this is where  tradeoffs are typically required between aisle width, grades, radius, turnout size, and run length to optimize the railroad for prototype operation.

The key is to start your planning with some notion of your limits and preferences (John called these Givens & Druthers) - then let the analysis and design begin.  Using 3rd Planit software once I mastered the basics I enjoyed the process. 

Ed Rappe

PS - I can testify that all the large Sunset 3rd Rail PRR motive power  (2-8-8-2 HH1, 2-10-0 I1, 4-8-2 M1a, 2-10-4 J1, 2-10-2 N1, 4-4-6-4  Q1, 4-6-4-4 Q2,  6-4-4-6 S1, 6-8-6 S2, 4-4-4-4 T1) will nicely operate around 54" radius curves without modification.

When I was looking at doing a layout in the back yard, I started with 72" radius (O-144 in hi-rail speak) but went to 96" radius. And that was with the plan to use 3-rail track. The reason is that equipment looks better and is better supported operationally on broad curves irrespective of how many rails you're running or where your couplers are mounted. The physics of a long train are disrupted by sharp curves (think about the SP Cantara Loop disaster up near lake Shasta). This applies in both a 2-rail and 3-rail context which is one of the bases for my frequent comment "just because we can doesn't mean we should". For an inside layout, I would try to design for 36" - 42" minimum radius with easements and select equipment/train length appropriately. Hopefully when I get relocated I'll either have a big interior space to work with or a nice back yard.

Good evening

I run scale size equipment, 80' passenger cars and 89' flat cars on super elevated 120" (60" radius) curves and I wish I could go bigger, no articulated locomotives.

Clem k

FWIW, I have a K-Line J1e Hudson that was converted to 2 rail with blind center drivers and it has no problems on 36"r. Might even make 27"r with long shank couplers. It depends on what models you are running.

It's great to see such a variety of ideas and inputs on this!

The decision as we all know is critical... most of our layouts are destined to be with us for years if not a decade or two.

Every one of you brings expertise to the table. It's funny to once again be reading John Armstrong's book cover-to-cover. It's too bad he can't see how his work has carried over the years and is still such a big part of this hobby.

These are exciting times for me. I think I'm going to get access to about a 16 x 30 ft. room upstairs strictly for my layout. Those numbers may change up or down but it's looking like room for a pretty nice "O" layout.

Please keep posting your thoughts. It all gets looked at and decided upon.

Thanks!

Chuck