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Minimum Radius for HO

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Minimum Radius for HO
Posted by Precast on Saturday, October 10, 2009 7:16 PM

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. 

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Posted by nfmisso on Saturday, October 10, 2009 7:23 PM

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. 

 

Nigel N&W in HO scale, 1950 - 1955 (..and some a bit newer too) Now in San Jose, California
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Posted by jecorbett on Saturday, October 10, 2009 8:25 PM

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.

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Posted by IVRW on Saturday, October 10, 2009 8:42 PM
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.

~G4

19 Years old, modeling the Cowlitz, Chehalis, and Cascade Railroad of Western Washington in 1927 in 6X6 feet.

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Posted by cuyama on Saturday, October 10, 2009 9:15 PM

 

IVRW
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:


Curve radius rules-of-thumb

Fortunately the rules-of-thumb work for all scales.

Tags: HO , Curve radius
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Posted by tomikawaTT on Sunday, October 11, 2009 12:01 AM

Real-world curve radii on a railroad I am actually operating:

  • 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.
  • 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.
  • 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)

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Posted by selector on Sunday, October 11, 2009 12:19 AM

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, to close the loop, and this post, it is all a synthesis between what you have to run that you like, and the space you have to fashion minimum effective radius curves.  It's almost a chicken and egg debate...what you buy because you gotta have it, and what curves you can squeeze into the room you have to play with.

-Crandell

 

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Posted by jwhitten on Sunday, October 11, 2009 12:32 AM

cuyama

 

IVRW
32 is kept as a guideline for realisticness.

"Realisticness"?

 

 

It's an industry term.

Modeling the South Pennsylvania Railroad ("The Hilltop Route") in the late 50's
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Posted by wabash2800 on Sunday, October 11, 2009 12:42 AM

 

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's would work fine.

But having said all of the above, using a smaller functional radius curve on a helix, for example, will give you a steeper grade which will limit train length. Personally in HO, I would never build a helix with a smaller radius than 30 inches (give me about a 2% grade) but I know of some that have built them down to 24 with very short trains. Another trap to note is that because a smaller radius curve will cause more overhang with longer equipment (even if you push the enevelope with truck mounted couplers) this can be problematic on multiple track unless the track spacing is widened. The wider spacing can also look very unrealistic. Another thing to consider on sharp curves is that sometimes coupling and uncoupling on a sharp curve can be difficult because of couplers not lining up.

I would recomend experimenting with sectional curved or flex track or possibly visiting other layouts and asking questions. 

 

 

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Posted by Anonymous on Sunday, October 11, 2009 1:18 AM

 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...Big Smile

The type of operation and equipment you like to see on your "road" finally determines your minimum radius!

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Posted by wedudler on Sunday, October 11, 2009 2:24 AM

 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

Pueblo & Salt Lake RR

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Posted by Bernie on Saturday, July 23, 2022 12:35 PM

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. 

 

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Posted by snjroy on Saturday, July 23, 2022 1:35 PM

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

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Posted by crossthedog on Saturday, July 23, 2022 1:51 PM

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

Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.

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Posted by crossthedog on Saturday, July 23, 2022 2:12 PM

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 

Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.

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Posted by John-NYBW on Saturday, July 23, 2022 2:32 PM

Bernie

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. 

 

 

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.

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Posted by doctorwayne on Saturday, July 23, 2022 2:40 PM

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

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Posted by BEAUSABRE on Saturday, July 23, 2022 6:07 PM

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

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Posted by JDawg on Saturday, July 23, 2022 6:53 PM

Precast

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. 

 

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. 

JJF


Prototypically modeling the Great Northern in Minnesota with just a hint of freelancing. Smile, Wink & Grin

Yesterday is History.

Tomorrow is a Mystery.

But today is a Gift, that is why it is called the Present. 

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Posted by BEAUSABRE on Saturday, July 23, 2022 7:05 PM

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.                                                                          I've based my Bellefonte and Nittany Valley off this idea. The B&NV being the YV, the PRR's Lewisburg and Tyrone at Bellefonte being the SP - with the added feature that just west of Bellefonte the L&T had an interchange with the PRR's Bald Eagle Branch between Tyrone and Lock Haven, which had some heavy duty railroading. That allows me to use just about anything the PRR had. I have an H6 and an H9 for the L&T local freight and passenger and an I1 (drag freight), K4 (Altoona-Lock Haven passenger), L1 (local freight) and M1 (Manifest freight Altoona-Lock Haven) for the Bald Eagle Branch. And a C&O T1 that I couldn't resist and a CNJ 4-6-0 that was a Christmas present from my parents and my first brass loco. I just say the Texas type is leased due a traffic surge and the Camelback is leased for the B&NV passenger service. And my PRR FT A-B lashup, GP3, GP20 and SD24 for when strange moods strike. 

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Posted by ricktrains4824 on Saturday, July 23, 2022 11:09 PM

The original post asked minumum radius required, but that answer varies greatly.

6 Axle GEVO's & SD70ACe's can run on 22" curves, but do they look good? That is up to you. Similar sized diesels can do these same curves. Me - I like to run trains, and I have a few 6 axle units that will be run on my 24" mainline curves. I do know that some 6 axles can operate on as tight as 18" curves, but not all. (And only if they are not coupled directly to larger-sized cars.)

Bachmann's 2-8-4 can handle as tight as 18" as well, but is better on larger 22" (or even bigger) curves. (Who doesn't like 765?)

But bigger is always better, with the caveat that you must be able to fit bigger for it to be better. Sometimes space is tight, so we build what we can, where we can.

So, what radius is a very hard question to answer, as there are too many variables to consider for a blanket answer, unless that answer is "It depends."

(But I've seen some really big equipment run on really tight curves in a pinch. One show I attended had a "show-stopper" on a 22" radii curve layout with zero derailments - a Bachmann Schnabel car! Everyone simply stopped to watch that thing, and everyone I saw was impressed!)

Last question about point to point with 42", or dogbone with 32" - You answered it yourself when you called the 42" minimum radii mainline "boring". Build the dogbone with 32" curves, and enjoy it.

Will my trains "look good" on my 24" radii curves? My definition of "look good" on a model railroad is that they run smoothly, and that the operator finds enjoyment in it. So they will look perfect to me. Smile

Your answer may be different, but when it comes to model trains, the only important answer about your layout comes from you. It's your layout, build it where you can fit it, at the size you can fit, how you will enjoy it. If others prefer something else, let them build their own layout their way. 

Ricky W.

HO scale Proto-freelancer.

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1: It's my railroad, my rules.

2: It's for having fun and enjoyment.

3: Any objections, consult above rules.

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Posted by fwright on Sunday, July 24, 2022 3:25 PM

Bernie
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'll point to 2 philosophies to help you choose.  John Armstrong (in a '50s MR article) separated model railroaders into 3 groups, based on operational preferences - dispatcher, spectator, engineer.

The dispatcher perfers the dispatcher role, keeping multiple trains (often each with their own engineer) running according to schedule and mission.  Designing a good dispatcher layout takes considerable planning, and effort in executionl.  In reality, there are very few dispatcher model layouts built in the US.

The engineer prefers to take his train over the line, doing what it is supposed to do (usually a way freight doing switching).  The engineer serves as train crew, couping/uncoupling as needed for switching.  Walkaround DCC is a very good fit for the engineer, a central console is not.  An engineer layout works very well for a solo operator - one train at a time.  Having more than one engineer simultaneously requires some thought during the design stage.  Scenery is nice, but usually second in priority to opportunities for switching.

The spectator layout is designed for the model railroader who likes to watch his train roll through a scene(s).  Scenery is usually crucial to the success of a spectator layout.  Your starter train set is a spectator layout at its very basic.

Because of train sets and the continuous run, most model railroaders start off as spectators.  Some-to-most eventually get bored with nothing but spectating.  Some will get bored with spectating more quickly than others.  Others never get bored with spectating - for them a continuous run layout is probably essential.

Curve radius is most closely related to the length of rolling stock you are going to use.  A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation.  Under this standard, min radius for a 40ft model car in HO (6" long) is 18".  Full length (80ft) passenger cars (12" actual) need 36" radius curves.  At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact.  Coupling/uncoupling on 3X is normally not possible.

I did some research on going smaller than 3x because I noted 3 rail O gauge trains were in the range of 1.2X to 1.5X, and I wanted to use 15" radius curves in HO.

2.5X (15" radius for a 40ft car) can be reliable IF trackwork is excellent, couplers have adequate swing, and underbody detail may need to be cut away to allow adequate truck swing.  Overhang will be nasty.  3 rail O gets to where they are with no underbody detail and trucks that can rotate 180 deg, truck-mounted couplers, and gross wheel flanges.

At 5X, coupling and uncoupling on curves is usually practical, and overhang is prototypical.

just my thoughts and experiences

Fred W

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Posted by riogrande5761 on Sunday, July 24, 2022 4:14 PM

fwright
A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation.  Under this standard, min radius for a 40ft model car in HO (6" long) is 18".  Full length (80ft) passenger cars (12" actual) need 36" radius curves.  At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact.  Coupling/uncoupling on 3X is normally not possible.

That was from an article published by he who cannot be mentioned here.  It's somewhat more oriented to what looks decent on curves as well as reliable operation.  My layout is a bit under that standard for example with minimum radius of 32", but only two curves that tight and one of them is the inner curve with a larger outter 34 1/2 radius.

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Posted by wjstix on Monday, July 25, 2022 9:44 AM

Just from a functionality point of view, most HO equipment today will take a 22"R curve, but a few things like Walthers passenger cars or BLI's 2-10-4 say they need a 24"R. In reality, some long cars may need some adjustments to the underbody to make 24"R curves however.

Stix
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Posted by fwright on Monday, July 25, 2022 11:59 AM

Joe didn't do the original research, he published the results and added his take.  My memory escapes me to be sure, but I "think" the original work was performed by the LDSIG within the NMRA.  My tiny contribution was to examine how toy trains were able to circumvent the rules of thumb, and reliably use much smaller than the rule of thumb radii.

Reality is that using NMRA standards with quality track and rolling stock, a 2.5X will usually work out functionally - if appearance is left out of the equation.

Fred W

 

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Posted by Doughless on Monday, July 25, 2022 1:13 PM

Bernie
)  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. 

The shape of my last layout was a dogbone with the double tracked area running along the long wall.  I operated it as point to point but wanted continuous running.

Operationally, I used the two turn back loops for industrial spurs, one being a load balloon track for a cement plant and the other a curved spur for corn syrup transload.  They were scenicked in such a way as to have them look like they ended after the curve (short of connecting to the back straight).  Operationally, the loco shoved cars onto the curved "spurs" and backed them off the same direction. 

The second main line along the wall served no operational function in the pt to pt mode.  It merely represented a Class I mainline that my shortline's trackage ran parallel to.  The interchange was nearby.

The turnback loops had a radius of 22 inches.  That told me that I wanted short cars on those loops during ops, and that's why I settled on shorty cement covered hoppers and corn syrup tank cars...typically 40 foot cars negotiating a sharp spur slowly...not unprototypical.    The longer cars typically ran over the rest of the layout...gentler curves.

During continuous running, it was merely a display situation and having the longer cars looking a bit out of place on the 22 inch radius curves was an acceptable tradeoff for having the continuous run.

It is possible to have both.  PtP that offers continuous run...even on something like a done bone shaped layout.

So your minimun radius is truly the minimum that the equpiment can handle, and appearences can be less of a priority because the cars aren't running on those two sharp curves during normal ops.

- Douglas

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    January 2019
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Posted by John-NYBW on Monday, July 25, 2022 1:57 PM

fwright

Curve radius is most closely related to the length of rolling stock you are going to use.  A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation.  Under this standard, min radius for a 40ft model car in HO (6" long) is 18".  Full length (80ft) passenger cars (12" actual) need 36" radius curves.  At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact.  Coupling/uncoupling on 3X is normally not possible. 

I hadn't heard that standard before but it seems like a reasonable one based on my experiences. Some brands of full length passenger cars operate more reliably than others so that has to be factored in as well. Just one correction. An 80 foot passenger car is only 11", not 12". 80 feet is 960 inches. Divide by 87.1 gets you almost exactly 11". Now an 85 foot passenger car is almost 12". An 80 foot passenger car would therefore call for 33" radius. That's very close to what I consider to be the minimum which is 32".

I designed my layout to have a 36" minimum curve on the mainline. On one curve I used a Walthers/Shinora #8 curved turnout which was advertised as having 36"/32" radius curves. I thought the 32" would be able to handle my full length cars. It was only after years of poor performance I learned that the inside curve was much tighter than 32" radius. Using my Ribbonrail gauges, I determined the inside curve was about 28" which explains why I had so many problems. I've since replaced it with a Peco #7 turnout which actually has broader curves than the W/S #8 and operation has improved tremendously. 

  • Member since
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  • From: Dearborn Station
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Posted by richhotrain on Monday, July 25, 2022 4:16 PM

John-NYBW
 
fwright

Curve radius is most closely related to the length of rolling stock you are going to use.  A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation.  Under this standard, min radius for a 40ft model car in HO (6" long) is 18".  Full length (80ft) passenger cars (12" actual) need 36" radius curves.  At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact.  Coupling/uncoupling on 3X is normally not possible.  

I hadn't heard that standard before but it seems like a reasonable one based on my experiences. Some brands of full length passenger cars operate more reliably than others so that has to be factored in as well. Just one correction. An 80 foot passenger car is only 11", not 12". 80 feet is 960 inches. Divide by 87.1 gets you almost exactly 11". Now an 85 foot passenger car is almost 12". An 80 foot passenger car would therefore call for 33" radius. That's very close to what I consider to be the minimum which is 32".

I have used that 3x standard in the past, and it is reliable. I have Walthers and Rapido 85' passenger cars as well as IHC 80' passenger cars, and John's calculations are correct.

I went down to my layout to measure these cars. The IHC 80' cars are just over 11", and the Walthers/Rapido 85' cars are just under 11.75". If you carry the calculations out four decimal points, you get 11.0218" and 11.7107", respectively.

As John indicates, they run well on 32" radius curves and, in my opinion, they look best running on 36" radius curves, or broader.

Rich

Alton Junction

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    June 2007
  • 8,709 posts
Posted by riogrande5761 on Tuesday, July 26, 2022 11:06 AM

My minimum is 32" radius, but most of my curves are a bit larger.  If anyone has a link to the topic on making Walthers passenger cars work better on curves, please past it in here.

Rio Grande.  The Action Road  - Focus 1977-1983

  • Member since
    September 2004
  • From: Dearborn Station
  • 22,943 posts
Posted by richhotrain on Tuesday, July 26, 2022 11:38 AM

riogrande5761

My minimum is 32" radius, but most of my curves are a bit larger.  If anyone has a link to the topic on making Walthers passenger cars work better on curves, please past it in here. 

If you follow the suggestion that I am about to make, you make hear some weeping and gnashing of teeth, but here goes nothing. There are lots of threads that touch on the topic of making Walthers passenger cars work better on curves. My suggestion is to start a new thread that will hopefully focus on this issue.

Rich

Alton Junction

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