Minimum Radius

Rail Dawg posted:

 

 

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.

 

 

 

Lots of experts on here!

 

Chuck

 

 

That's easy to explain. It's because their 3 rail line of track stops at 0-108 (54" Radius).

I was once told that any 2 rail steam locomotive will run on 72" radius curves but then I read on this forum that even that wasn't true. I think it was Bob2 that said he had locomotives that wouldn't run on 72" radius curves but I could be mistaken on that. I'm making the same decision on my railroad and it looks like the largest curve I will be able to fit as a minimum is the 54" curve. I would rather limit myself somewhat on equipment to run than to make the compromise and go to 3 rail track. If I can't run some of the older 2 rail locomotives so be it. All my locomotives are MTH, Lionel, or Sunset save for one Lobaugh.

Northerns and ten-coupled with full tail beams, narrowed for model use, will have trouble on 72" radius.  The tinplate models generally come without any tail beam, or a giant cavity where the wheels swing, and undersize cylinder blocks with elongated wheelbase engine trucks.

Understand that a real locomotive has a cradle under the firebox that is full frame width.  None of us can have that.  We taper the tail beam inward as it goes to the rear.  And those are the models that still have trouble with 72" radius.  In 2-rail, if the wrong wheel touches the frame, everything stops cold.

Gentlemen,

    Looking at his question from an engineering stand point, the answer comes down to, space and Engines he is planning to run on his layout, only he can decide these variables. The reality is his actual space dimensions and which Engines he has, or is going to purchase.  Nobody knows that but him, we can advise all we want to no avail. Always run as large a curve as you can for the space you actually have, and purchase Engines that will accommodate the track plan.

PCRR/Dave

That is certainly true.

but the reason folks ask these kinds of questions is to gather opinions.  The reason we respond is to offer opinions.

Opinion.

Steamboy, please don't be turned off.   Yes this thread was started on the 2-rail forum, but it is open to anyone.    I think what was meant by the comment is that generally in 2-rail, guys refer to curves by the radius rather than diameter, so 072 is 36 inch radius.   However after all that, you need to double the radius to calculate the width of a turnback loop

Rail Dawg,

My opinion is that you start with what you want to model and how you want to operate.      Then work on the compromises to come up with a track plan to fit into your available space and get you some your objectives.

John Armstrong called these "givens and druthers".    Givens are the space, time and money considerations and maybe existing models that you will never part with.    Druthers are things that you want to have on your layout or do with your layout.     You probably want to list both.    Then arrange your druthers from highest priority to lowest priority on the list.    then given the limitations of the "givens" list, try to fit as many druthers in as possible.

By the way, I have a fleet of USH PRR 2-10-0s and a Max Grey 2-10-4 and they will all negociate 54 inch radius.    the 2-10-0s (10 coupled)  will go around 48 with ease if you block the center driver so it cann't fall down inside the rails on the outsid eof the curve.    Now these do have blind drivers as the prototype did when built.

Good one.

 I did it the opposite way - I built a train shed with a maximum possible radius of about 64", then realized my favorite SP Decks would never make it.  A bit more concrete, a lot of carriage bolts, a new roof, etc, etc, and now I have a 74" loop.  It is enough for the Decks, and almost accepts the 4-12-2 in 17/64 scale, but darn - the SP Daylight articulated coach will not quite make it.

And you know my solution - a new train shed.  This is getting expensive!

Fact.

Glad somebody resurrected this thread.  I no longer understand the other one.

prrjim posted:

By the way, I have a fleet of USH PRR 2-10-0s and a Max Grey 2-10-4 and they will all negociate 54 inch radius.    the 2-10-0s (10 coupled)  will go around 48 with ease if you block the center driver so it cann't fall down inside the rails on the outsid eof the curve.    Now these do have blind drivers as the prototype did when built.

That is cool!

I recently built a layout, handlaid and flex-track, with 54" minimum radius including "spiral" transitions from straight to 54" radius.  I am very happy with how my modern diesels and rolling stock look, including the Lionel 89ft autoracks.

I don't have any steamers though. 

I'd like to add to PRRJIM's experience with 54" minimum radius.  For decades I ran Westside J1 2-10-4's, Q2 4-4-6-4, M1's, 4-8-2, USH L1's Overland M1b, and virtually all the Sunset PRR power from a S1 6-4-4-6 on down around a railroad with main line super-elevated 54" curves (branch line 46" curves).  None of the large Sunset locomotives required alteration.  The Westside/KTM's J1's and Q2 did require some relatively minor mods to provide for additional lateral motion in drivers 1 and 5, and swing clearance for the rear trailing truck wheel. Once painted none of the changes were noticeable - even at eye level.  My DC area O scale friends running heavy PRR, WM. B&O, and N&W rosters also use less than 72" radius curves to maximize operation interest – some in relatively modest basement spaces. 

For appearance reasons you may want to go 72" radius and up - but don't feel you have to do it to run a large variety of O scale locomotives and full length passenger cars.  My close coupled diaphragm equipped 80' passenger cars did just fine on 54"r. Wider radius curves do look better than tighter ones but they typically come at a price of track possibilities and aisle width - especially if the route is folded down the middle of the room.  My recommendation is to go with a mix of radius.  Wider in places where you will be viewing the trains from the outside of a curve, and tighter where the curved is viewed from the inside, or where it can be disguised by scenery features or structures (like a roundhouse complex).  Building the railroad at higher elevations serves to improve the look of the railroad as a downward viewing angles tends to call attention to sharp curves. 

While at it we should also mention track centers.  The PRR minimum was only 13' (3 1/4") on tangents.  My compromise was 3 1/2" on tangents and 3 7/8" centers on my one 60" radius curve.  Changes to track spacing can nicely be made in the length of the easements in and out of the curves.  The 3 7/8" centers will nicely clear 80' passenger cars passing my largest locomotives. If you plan to run Big Boys or other large articulateds with wide swinging boilers empirical testing can be used to find out what minimum track center they will need.

My recommendation is to size the minimum radius to the prototype equipment you want to run, and then use the layout design concepts in John Armstrong's book to maximize the operational interest of your railroad.  A blend of learning about the prototype, buying/building/detailing models related to the prototype, and operating the railroad with friends has served to keep the hobby fresh for me. 

Ed Rappe

A comment about the difference in curve terminology between scale model railroading and traditional Lionel 3 rail.   Lionel's curves were expressed as the diameter of a circle of track measured to the outside edge  of the traditional metal ties.  Scale model railroaders following NMRA practice measure curves by center line radius - not the outside of the ties.  Since Lionel metal ties are 2 1/4" wide - tinplate O72 track equates to 33 3/4" radius in scale model railroading terms - a bit tighter than one might expect.

Ed Rappe

A further comment from the Rockford O Scalers:  When we first built corners for our modular layout, since most of us were HO modelers, we figured that by doubling the size we were used to in HO (30' and 32" radius) we would be able to run most anything, so we went with 60" and 64" curves for our double track main lines.  However ( you know where this is going!) we soon found out that "scaling up" doesn't work that way.  These curves could accommodate an F unit or Geep but anything larger either looked bad or wouldn't make the curve (including a Westside PRR 2-10-4).  After putting up with these limitations for a couple of years, as mentioned in my previous post, we built new corners containing 88" and 92" radius curves.  Operationally, these curves work fine and will run anything, but it is interesting to watch a video taken at track level of 85' passenger cars going through these curves as they still look almost toy like!  This just shows you how broad a prototype curve really would be when reduced to 1/48 scale!  

Good looking Daylight and great module!

Great topic.  Unless I missed it above -- it isn't just about large vs. small engines.  Another factor is the wheelbase of the more rigid part of an engine (even though various brands have varying lateral articulation in coupled drivers).  My example would be my Sunset UP 844 with 4 each 80 inch drivers tied together (4-8-4) has a longer drivers  wheelbase than my Sunset UP Big Boy with the same 4 drivers for each engine (two 4-8-4's) under the boiler but smaller drivers and therefore a smaller  wheelbase for each set.  So, the UP 844 is the real minimum radius test.  There are an a huge number of factors like this that can bit one in the XXX if one tries to fine tune minimum radius down to a close minimum just to have more track.    I go with the bottom line majority well stated above which is make the minimum radius, eased or not, as large as you can possibly make it. 

Frank McCabe posted:

A further comment from the Rockford O Scalers:  When we first built corners for our modular layout, since most of us were HO modelers, we figured that by doubling the size we were used to in HO (30' and 32" radius) we would be able to run most anything, so we went with 60" and 64" curves for our double track main lines.  However ( you know where this is going!) we soon found out that "scaling up" doesn't work that way.  These curves could accommodate an F unit or Geep but anything larger either looked bad or wouldn't make the curve (including a Westside PRR 2-10-4).  After putting up with these limitations for a couple of years, as mentioned in my previous post, we built new corners containing 88" and 92" radius curves.  Operationally, these curves work fine and will run anything, but it is interesting to watch a video taken at track level of 85' passenger cars going through these curves as they still look almost toy like!  This just shows you how broad a prototype curve really would be when reduced to 1/48 scale!  

Beautiful work, Frank. Are the module specs available? I like to collect them for reference.

After drawing out several different designs for a layout in my space (a little less than 20' x 40'), I settled on 108" radius in order to provide a good visual setting for my articulated engines. The large curves include "spiral easements" (actually, approximations laid out by the "bent-stick and offset" method). In my opinion, the appearance of a large articulated engine entering and leaving these big curves pulling a train of around 30 standard 40-foot and 50-foot freight cars is very pleasing and more than makes up for the real estate the big curves gobble up in the room. I built my layout mostly for the occasional fun of running a fairly long train that looks good on the track and is fun to watch, rather than for operation, or switching, or as an attempt to reproduce anything more than just a small section of single-track mainline. 

Other people will have different desires and goals in building a layout, but if you want to operate some large engines and have them look OK (rather than simply ridiculous), then I would choose the largest radius possible and accept the limitations that follow. Of course, not everyone will agree. 

Keystoned Ed posted:

I'd like to add to PRRJIM's experience with 54" minimum radius.  For decades I ran Westside J1 2-10-4's, Q2 4-4-6-4, M1's, 4-8-2, USH L1's Overland M1b, and virtually all the Sunset PRR power from a S1 6-4-4-6 on down around a railroad with main line super-elevated 54" curves (branch line 46" curves).  None of the large Sunset locomotives required alteration.  The Westside/KTM's J1's and Q2 did require some relatively minor mods to provide for additional lateral motion in drivers 1 and 5, and swing clearance for the rear trailing truck wheel. Once painted none of the changes were noticeable - even at eye level.  My DC area O scale friends running heavy PRR, WM. B&O, and N&W rosters also use less than 72" radius curves to maximize operation interest – some in relatively modest basement spaces. 

 

For appearance reasons you may want to go 72" radius and up - but don't feel you have to do it to run a large variety of O scale locomotives and full length passenger cars.  My close coupled diaphragm equipped 80' passenger cars did just fine on 54"r. Wider radius curves do look better than tighter ones but they typically come at a price of track possibilities and aisle width - especially if the route is folded down the middle of the room.  My recommendation is to go with a mix of radius.  Wider in places where you will be viewing the trains from the outside of a curve, and tighter where the curved is viewed from the inside, or where it can be disguised by scenery features or structures (like a roundhouse complex).  Building the railroad at higher elevations serves to improve the look of the railroad as a downward viewing angles tends to call attention to sharp curves. 

 

While at it we should also mention track centers.  The PRR minimum was only 13' (3 1/4") on tangents.  My compromise was 3 1/2" on tangents and 3 7/8" centers on my one 60" radius curve.  Changes to track spacing can nicely be made in the length of the easements in and out of the curves.  The 3 7/8" centers will nicely clear 80' passenger cars passing my largest locomotives. If you plan to run Big Boys or other large articulateds with wide swinging boilers empirical testing can be used to find out what minimum track center they will need.

 

My recommendation is to size the minimum radius to the prototype equipment you want to run, and then use the layout design concepts in John Armstrong's book to maximize the operational interest of your railroad.  A blend of learning about the prototype, buying/building/detailing models related to the prototype, and operating the railroad with friends has served to keep the hobby fresh for me. 

Ed Rappe

Ed, you win the prize for most useful post in this whole thread. Opinion is one thing, but when it comes to spending 10's of thousands of dollars (or more) I prefer to read about proven results!

Thank you!

At the 2010 0 Scale Nationals in Towson MD I had a 3' X 21'  test track with 8 different radii from 49.5 thru 72". 

Most all engines passed on the 54"  curve.  One  Westside PRR J had a tendency  to climb the rail head.  It performed well on the 56" radius

It was interesting to see an engine work back and forth to find it's minimum radius.

Tom, good job. Wish I would have seen it. Perhaps, just maybe, we need a Model RR database of Radius Minimums. From the smallest 4 wheel caboose in Z gauge to the mighty Allegheny on O Scale, and all models in between. Anyone wants to know what a minimum radius is, look it up. Maybe the NMRA could sponsor the Database. I know there would be a number of variables as which couplers are used, and even what is any center drivers are blind, etc. Also even what other conveyance the unit of discussion would be coupled to! This was only a passing thought...Sigh...

Dan Weinhold

Here are some shots of 60 inch radius from some non-hot-air-balloon angles. Sorry for the line poles but I think the first car shows a reasonable representation of what you'd be in for at eye level. The second shot is straight from a standing position from a regular viewing angle. It shows the inside of the curve from another direction. Anyone who tries to jump on the outside of the curve to get that view will get a beating. The layout was designed with this in mind.

Thanks or posting the shots of the full length cars on 60" curves Chris .  I've seen his layout many times and he's packed an amazing amount of great looking and running heavy mainline railroading in a modest space - something he could not have done if he listened to folks saying you need 72" + curves to run full length passenger equipment and big steam.   For some inspiration check out this drone video of N&W 611 running in the mountains.   https://www.youtube.com/watch?v=Ub5H0BFQk88

Ed Rappe

I've realized that there are two posts titled minimum radius here.   I started the other post in December 2015, and had a lot of good feedback on my layout in progress.  I had posted some images but they were small and unreadable so using the snipping tool as recommended I'm posting them again in hopes they are readable this time. 

Scott Thompson

PS I change the other post to Minimum Radius Advice?  Hopefully there are no others the same.

Scott Thompson

I realize everyone here is talking about larger steam locomotives and full sized passenger cars but if you have a smaller space, you can still enjoy a layout if you carefully select your power.  Here are 2 videos of  an unmodified Glacier Park SP 2-8-0 handling 36" radius curves.  On the layout the entire 36" curve will be hidden in a tunnel but the rest are from 42 to 48.  Those are 60' coaches.

Layout:  

Test S curve:   Please pardon the poor quality but I think this was my first video attempt.  36" code 100 from Fast Track Jigs.

The reason I mentioned selection of power is I've found some models are better engineered to handle tighter radius than others.  For example, a 3D Rail 2-6-0 will not handle under 48" while my 2-6-0 and 4-6-0 Glacier parks will handle 36.  The 4-6-0 did require a 1/8th longer draw-bar and 2 plow looking things by the front truck removed.  All of my diesels handle the 36".  A CF7, SW1, RS1, S2, Whitcomb.

My layout space is 20 x 21 feet.

Thanks,

Peter

Scott, interesting....this thread opened with "If space wasn't a concern"  Which could be understood as Maximum Radius Advice".

Ed, I'll never forget the photo you posted over ten years ago  of full length passenger cars leaning into your earlier super elevated 60" +/-  radius  Horse Shoe Curve which was nothing less than spectacular.

I believe it was in response to my "you need 72" blah,  blah. blah"  comment.

You, Chris and Lee Hart have shown what magic can be worked with comfortable curves when one applies the masters touch to the overall scene.  IME, the issue boils down to symmetry of effort.

Viewing excellent modeling vs looking at a modest curve on a flat piece of plywood is a totally different experience.

Do you make house calls??

PS:  If you want to see a compilation of Ed's Horseshoe Curve, John Armstrong's Cattaraugus terminal & Ted Stepek's RR check out MR's  GMR 2016.  David Vaughn and a crew of many married these into what may be called an 0 scale museum.  A fantastic 1000' mainline of 1/4" RRing.  Tom Thorpe

Hi All,

Here is a photo of the Train of Tomorrow running on the Rockford O Scalers 92" radius outside main (as I mentioned in my previous post, the inside is 88" radius.)  I agree with previous comments that adequate double track spacing and the use of easements when entering curves is very important to assure both good operation and appearance.

Chuck,

Track radii should be what looks good to you with the longest locomotive or piece of rolling stock that you will be operating. I would get some flex track and experiment.

Do not believe what the locomotive manual says about minimum curves.  If you are running scale size articulateds you need minimum of 088.  They simply look ridiculous on 072 curves.

Also, if you are running two curves adjacent to each other, the distance between the curves needs to be at least 5.5" to run articulated engines.  If less than 5.5" the boiler outswing will catch cars on the adjacent track.  I have 102 and 088 on dual elevated loops with 5.5 to 6.0 inches between the tracks on curves.  That will easily clear even the Big Boys.

Also - super elevate the outside rail 1/16".  That may seem like a little, but it makes the curve less frightening and more realistic looking when running trains. 

Do not forget the double stack and large freight cars, the swing on them is tremendous.

bruce

bruce benzie posted:

Do not believe what the locomotive manual says about minimum curves.  If you are running scale size articulateds you need minimum of 088.  They simply look ridiculous on 072 curves.

Also, if you are running two curves adjacent to each other, the distance between the curves needs to be at least 5.5" to run articulated engines.  If less than 5.5" the boiler outswing will catch cars on the adjacent track.  I have 102 and 088 on dual elevated loops with 5.5 to 6.0 inches between the tracks on curves.  That will easily clear even the Big Boys.

 

That depends on what articulated models you are operating. I run A's and Y's and 80-85' cars on 56" and 60" with 4" centers. I don't care to run Big Boys, Challengers or others and never will, and would not design my layout for the chance that someone might want to run this or that engine at some point on my layout.  

I'd reiterate, as a starting point figure what your engines CAN negotiate. The information in the quote above may be good for Big Boys, but is absolutely incorreect and irrelevant for some other railroads. Figuring what your engines can negotiate will give plenty of leeway from a design standpoint and especiallly in hidden areas. From there you can put in cosmetic curves if you'd like.

When people say "you need" some certain minimum for cosmetic purposes, it likely confuses people about what minimum they really need  to operate in 0 Scale. Checking out what curves look good to you is certainly something to investigate, but is different for everyone. There is no authority here on that. 

 Tom,

Thanks.  I have been taking many photos of the layout for an article. I think you are going to like it. Right now I'm not doing scenery for others because I don't want to make my hobby a job but I would not rule it out in the future. 

Well said Chris.  I typed a reply to Bruce's post and am glad I didn't post it.  Each is entitled to their own opinion but not to their own facts.

Ed Rappe

bruce benzie posted:

Do not believe what the locomotive manual says about minimum curves.  If you are running scale size articulateds you need minimum of 088.  They simply look ridiculous on 072 curves.

Also, if you are running two curves adjacent to each other, the distance between the curves needs to be at least 5.5" to run articulated engines.  If less than 5.5" the boiler outswing will catch cars on the adjacent track.  I have 102 and 088 on dual elevated loops with 5.5 to 6.0 inches between the tracks on curves.  That will easily clear even the Big Boys.

Also - super elevate the outside rail 1/16".  That may seem like a little, but it makes the curve less frightening and more realistic looking when running trains. 

Do not forget the double stack and large freight cars, the swing on them is tremendous.

bruce

What the heck are 088 curves (you typed zero-eight-eight)?  Do you mean O-88 (with the letter O)?   If so, are you talking about 3-rail steamers?

If you did mean 88" radius curves (which is the proper nomenclature on the 2-rail forum), I'd like to know how wide your layout is?  

Was anyone else here completely confused by Bruce's post?  If we all follow the same convention (ie, 36' radius, 72" radius, 54" radius) and write it out that way, it should facilitiate better discussion and idea-sharing.

christopher N&W posted:

 

I'd reiterate, as a starting point figure what your engines CAN negotiate. The information in the quote above may be good for Big Boys, but is absolutely incorrect and irrelevant for some other railroads. Figuring what your engines can negotiate will give plenty of leeway from a design standpoint and especially in hidden areas. From there you can put in cosmetic curves if you'd like.

When people say "you need" some certain minimum for cosmetic purposes, it likely confuses people about what minimum they really need  to operate in 0 Scale. Checking out what curves look good to you is certainly something to investigate, but is different for everyone. There is no authority here on that.

Well stated - I'd only add that this is also something to be done within the context of the available or allotted space.

Yes, Bruce's post was tough to get on the first reading, but his use of O-88 should be a flag to all of us.  The ones that are harder to deal with are the ones that say O-88 radius, when they are discussing diameter.

When I read it, I sort of assumed he meant 88" radius, which is a wonderful thing to have if you have the space.  And since the OP said space was not a concern, and since thread drift is frowned upon here, the obvious answer is 88" radius or greater.  You can have tailbeams. Your passenger cars can be properly coupled. And yes, easements and superelevation.  Wish I had that kind of space!

072 and 088 are commonly used terms for 72 inches and 88 inches diameter over in the 3 rail world.   3 rail guys commonly use diameter speak.  2 rail guys commonly use radius speak.   No disrespect intended but I'm surprised that anyone is confused by this lingo as it's so widely used in all the magazines and catalogs and is all over the internet.    

I'm really enjoying this topic.  It comes around fairly often and always comes to similar conclusions but brings out good points along the way that amplify on John Armstrong's words.  I got my first edition copy of John Armstrong's "Track Planning For Realistic Operation" lo these many decades ago.  All of this is covered in the book and it's reassuring that John's time tested planning factors are still holding up lo these many decades later.  And while there's nothing new in this topic, no breakthrough, it's interesting to see how guys are currently applying this info.     

I highly recommend that anyone who is designing and building a layout snag a copy and read it cover to cover -- and then ask amplifying/clarifying questions on the forum.  "Ye shall know the truth and the truth shall set you free".  Yep.

"Up and back down" in 12 feet is a very heavy grade (Hudson5432) -- perhaps you meant in 120 feet?

Assuming the train is climbing 4.5 inches up and 4.5 inches down to be able to do that in 144 inches would be a very high and very unrealistic grade of 6.25% up and down. If the height needed to go up is more than 4.5 inches then of course that would increase the percentage of grade.