Hey Guys,
Just getting started on a shelf layout. What’s a good minimum number to use on a radius? I want to make a complete 180 degree U turn. Thanks in advance.
For what kind of equipment?
Many years ago in MR, there was a picture of an 0-4-0T steam locotive going around a circular layout where the inner rail was a silver dollar.
Close to the other extreme, is the MTH 4-12-2 with the chassis locking plate installed (see MR 11/09 pg 78) has a minimun radius of 42 inches. WIthout the locking plate, it will do 22".
If you stick to 40’ and shorter cars, smaller steam locomotives like Bachmann’s 2-8-0 or smaller four axle diesels like GP7 and RS3; 18" radius is do-able.
What should your minimum radius be. My answer would be the largest radius your available space can handle. There are two issues when it comes to radius. What is the minimum radius your equipment can negotiate and what is the minimum raidus it will look good running on? The latter requires a much larger radius than the former. Sectional track is widely available in 22" and 18" radius but 15" is still around as well. In order to make their equipment marketable to a large segment of the hobby market, manufacturers try to develop equipment that can at least negotiate 22" radius track. While large locos and full length passenger cars might be able to handle sharp curves like that, they are not going to look good doing so. Model railroad curves, even on large layouts with very broad curves are going to be much sharper than the prototype curves so some compromise is going to be in required. Regardless of the size of your layout, the broader you can make your curves the better. Your railroad will look and operate much better. I have never heard of anyone complaining that they made their curves with too large a radius.
As nfmisso said, it depends on what you run. If your running 85 foot Passanger cars, a good minimum Radius is 32. However, if your just running a small beginners layout, 22 is good as well. In a case of dire needs, 18 will do. But before you kick the bucket, I would say 15 is good for REALLY small locomotives, no bigger than 4-6-0, and VERY TINY cars, no bigger than 36 feet. But if it is Modern or 1950s, 32 is kept as a guideline for realisticness.
“Realisticness”?
32" is much too broad for many smaller model railroads in HO. If one chooses too large a minimum radius, it can be just as problematic as too small, since it so severely limits what can be accomplished in a given space.
This guideline is based on some experienced modelers’ findings from the Layout Design SIG site:
Fortunately the rules-of-thumb work for all scales.
Real-world curve radii on a railroad I am actually operating:
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Main line - shorty (about 10 inches long) passenger cars, 2-8-2 steam, a few long rigid-frame diesel-hydraulics and long freight cars - 610mm radius (24 inches) with easements.
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Secondary trackage - no passenger cars, medium freight cars, electrics and diesel-hydraulics with no more than 8 drivers - 500mm radius (19.8 inches) with easements.
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Mineral hauling shortline - short and articulated cars and short-wheelbase steam - 350mm radius (13.8 inches) with easements.
Leaving out the easements would increase the radii required by at least 100mm.
I have proved by experimentation that the Mantua 2-6-6-2T will take a 305mm radius (12 inches) - which is just about the same as the 1:1 scale 68 degree curve the prototype was designed for.
Incidentally, the 0-4-0t that was photographed on the Silver Dollar Central was the original Varney B&O “Little Joe,” AKA, “Dockside,” not to be confused with the MILW electric of the same name.
Chuck (Modeling Central Japan in September, 1964 - on some pretty tight radii)
Byron, I am pretty sure he meant “realisticity”.
The minimum radius in HO is a synthesis of what you have to push around the curves and the shape and dimensions of your overall track plan. As stated earlier, some larger steamers in HO will go around 18" curves. We all learn to live with compromises. We all learn that there is a better way to do things after we accept what “better” means to us. Often, for most of us, better usually is a combination of more/larger. We get more engines, and usually not the same kind. We develop a hankering for a larger steam or diesel monster, and there is where we realize that we shot ourselves in the foot…we didn’t plan ahead, or we bought the wrong monster.
As a general guideline, subject to individual bias, the smallest practical curves in HO are accepted widely to be in the order of 18". Not a hard and fast rule, but a guideline. Mountain logging operations had tighter curves in scale and nasty track of a temporary kind.
For those with the room, and who know not to fill all their space with every conceivable track apparatus and length, but to keep tracks to an operational and effective minimum, curves between 24 and 30 inches are highly desirable, and would be called medium curves. The lower limit in that range, 24" is what Walther’s states is the minimum to operate their heavyweight passenger cars. I’ll bet 100 people who post here regularly would say “baloney!” They’ll tell you they had to alter their cars or widen their curves before the derailments went away looking for another layout to haunt. (I have it on good authority that they are busy to this day…)
Curves in excess of 30" radius are generally considered broad curves, and if laid properly are essentially trouble free. They look the best, too, for longer rolling stock and large engines.
But
It’s an industry term.
I agree with jecorbett. IIRC, some years ago someone wrote an article on the subject in an NMRA magazine. They called the two types of curves, “functional” and “cosmetic”. Functional curves were the smallest radius curves that your trains could run effectively on and cosmetic were the curves that your equipment looked more realistic on.
So, of course, this is variable depending on what type of equipment you are using. And if you would like to use the concept to its best advantage, you can use the smaller functional radius curves in hidden areas and the cosmetic curves where they will be seen to get more bang for your buck in layout design. But when I say functional I’m not necessarily talking about the absolute smallest radii your trains can run on as that might be asking for problems in hidden areas. I’m taking about the smallest radii that will be reliable.
So if you are running old time trains with small steam locos and short cars you can get by with tighter curves both functional and costmetic, say, 15 and 18 inch radius in HO. But obviously, with larger locos and longer cars you need much larger radii. For my layout in the early 50’s with medium steam locos and long heavyweight passenger cars, my functional is 30 inch and my my minimum cosmetic is 42 with spiral easments. Even with 42, I have some overhang btw the long cars. Most medium size diesels will run fine on 18 inch curves and No. 4 turnouts though some need 22 and 22 might be a better choice anyway for reliability. But if you are modeling long autoracks and doublestacks it those smaller radii might not cut it.
I agree with what someone else here said about wasting space with too large of curves. But the other fellow that had a point about wide radius curves was not that far off. It depends on your priorites. For example, I use No. 8 or larger turnouts on my mainline because I think they look a lot better than No. 6’s, but No 6
Linn H. Westcott classified radii as follows (HO scale)
- Sharp: 18"
- Conventional: 24"
- Broad: 30"
With sharp curves, you´ll limit your operation to short wheel-base locos and rolling stock, with conventional curves, you should be OK with most of the R-T-R equipment currently in the market, but if you intend to run those 85" or 89" - cars, broad curves seem to be the minimum.
If you intend to operate those Big Boys or UP 9000´s - well, then you´d better go for 42" and above, if you want them to look OK on the track…[:D]
The type of operation and equipment you like to see on your “road” finally determines your minimum radius!
You minimum radius depends heavy on the equipment. For this shay and short cars I can run it on my Pizza layout.
At my mainline at Westport Terminal I have 47’'.
I’ve widened the gauge for this 8.7’’ radius ! My 44-ton will run there too.
Wolfgang
I know this is an old question, but this is something I’ve been thinking about recently.
I know, “Make your radius as big as your space allows.”
I also know, “Choosing too large a radius limits what you can do.”
I’m thinking if I have, for example, a 14’ by 30’ space (a pre-manufactured garage to be delivered onto my property, the largest available).
I have two options:
1.) A true point-to-point with one end on the south-west corner, the mainline running along the north wall, and the other end on the south-east corner. I can have realistic broad 42" curves (or even larger), but a short boring mainline.
2.) A dogbone with one loop on the south-west corner, double tracks along the north wall, and a loop on the south-east corner, for continuous running. Then I can add two wyes at each end and have two stub terminals sticking out into the center to simulate true point-to-point and treat the dogbone as if there’s a mainline and a separate freight line connecting the two distant urban centers. This is actually prototypical in a few places. This will be a fun layout to operate or to just watch the trains run. But the mainline minimum radius will have to be 32", and even less for the wyes approaching the terminal stations.
It depends on many factors, mainly the type of equipment you want to run and the type of operations you will be doing. What era and industries are you thinking of?
Simon
For me, the continuous run is a deal breaker. I have to be able to let the train run. It runs while I’m repairing cars, or while I’m just standing and thinking how I will solve a problem. It’s a personal choice, but it’s the first and most important choice for me and it very much determined the shape of my layout today, which is not ideal, but it provides me with a loop and also a small yard and some switching opportunities. A point-to-point would drive me batty with frustration unless it was very long with lots of operations along its length. Your trackage may vary, of course.
-Matt
And reading carefully your two options again, it seems to me the only benefit of your first option (point to point) would be enviable 42" radius curves, and that benefit I reckon as dubious considering that you’d lose the continuous run and be stuck with a mainline that you would assess as boring.
If you go with the second option, you get your continuous run (grandkids will love you if they don’t already!) and still have 32" curves, which anything will run on, even long passenger cars. (I don’t worry about passenger cars not looking realistic on curves – that’s a luxury for people with more space than I’ll ever have. My mainline curves are minimum 24" – my plan was to use mainly 40-foot freight cars, which I do, and I just hoped that Athearn’s shortie heavyweight passenger cars would look okay rounding them. But I ended up finding Atlas/Branchline regular length (72-foot) cars and they look really good on my layout, at least to me. If I really want to make myself unhappy, I can squint enough to see that their overhang on the curves is too much to be prototype, but allowing this to smirch my enjoyment would amount to contravening my first rule of the hobby – that’s it’s supposed to be fun.)
-Matt
I’m not sure why you want loops and a wye at each end. Both eat space but you only need one or the other to turn trains.
Allen McClelland did have a loop track incorporated into a wye on one end of his point-to-point V&O layout but the loop was not used to turn trains. He operated it as a wye. I can’t remember his reasoning for having a tail track of the wye loop back and connect to the lead for the wye.
The minumum mainline radius on my layout is 30", and occurs only on three legs of a dead-ended wye, meant for turning cars or locos and 80’ heavyweight passenger cars, too.
Otherwise, the curves are anywhere from a 32"radius up to about 48".
My layout is in an oddly shaped room, and is meant to be a point-to-multi-point set-up, although I do have a lift-out at the train room’s entrance, which allows for continuous around-the-room-running when visitors (or grandkids) want to see trains running in circles.
The partial upper level is accessed from the main level, but dead-ends at two different points which act as staging tracks.
Wayne
That "someone"was probably John Armstrong, who was an advocate of not just following the edge of the basework, Here’s an example of a cosmetic curve on a modern layout - imagine a train sweeping through that 
Track Planning for Realistic Operation by John Armstrong (1998, Trade Paperback, Revised edition) for sale online | eBay
If you are running small 4 axle road units with smaller 40-50ft cars then 18 is the smallest that should be done. 22 is better.
For shorter passenger cars, 24 is a good rule of thumb, although they look best on 30 plus.
I have run 40, 50 and 60 ft cars with smaller GP’s ano RS units on curves as sharp as 15 in. Do I recommend it? No, but it’ll do in a pinch.
When I was a member of the old Summit-New Providence Club in the Sixties we had the “show loop” - turnouts and crossovers that allowed us to convert our point to point mainline, branchline and short line to continuous running when we had our annual open weekends. They were unobtrusive, never used during normal operation and just used when we “wanted to run trains” for the public Second, John Armstrong had a design for a basement sized layout based on the Yosemite Valley, a shortline that ran between a SP (and ATSF - not modeled) interchange at Merced to El Portal at the entrance to Yosemite National Park. It was impressive with heavy log trains to the sawmill and Pullmans for park visitors - not your streak of rust that “shortline” says to so many. Anyway, the SP was a simple loop around the edges with a dual directional fiddle yard on one side and the interchange (station, small interchange yard, YV servicing facilities) on the other - most to be eventually concealed from view with the tracks coming around a bend into the interchange area and disappearing (under a highway bridge…maybe a tunnel…I forget that part) at the other end. So if you left the center track clear in the fiddle yard, you could run the SP as a continuous loop. He advocated building the SP first as it would allow you to perfect your benchwork, track laying and wiring skills, before moving on to the larger and more complex YV. Also, as the YV was obviously a multi-year project, it would allow to get trains up and running quickly to keep interest from flagging. And when you needed a break from construction, you could “run trains” to inspire you again. And of course,as YV progressed, you could begin operating over completed sections of that as well. Man was a genius. &