Curve Radius

[trainsarecool]

Does anyone have suggestions for the best curve radius in HO?

 

[Lone Wolf and Santa Fe]

Here is a list I made up of minimum radius for different type of equipment.
Toys = 18”
Most scale models = 22”
Scale models with accurately detailed fames and coupler pockets = 24”
Steam Locomotives = varies up to 30" or more.

Those are them minimum at which they will operate however many people will complain that those are too tight and that long cars look horrible overhanging the track. It is more obvious when looking down at a layout than on an eye level layout. They also have other issues with S curves and can’t be right next to a turnout without problems.

Best practices is to have curves in the 30” to 36” range.

[7j43k]

I chose 48" for my mainline minimum because most real railroad equipment can handle that curve.  So, if I were to be blessed/cursed with an EXACT model of a piece of rolling stock, it still should fit.

For branchline curves, I expect to go with 36".  And for industrial trackage, 24".

 

 

Ed

 

[cuyama]

trainsarecool

Does anyone have suggestions for the best curve radius in HO?

Welcome to the forum. "Best" is a tricky term. It depends on what era you model and the types of cars and locomotives you will be running. The length of your longest cars and engines is a good metric. This must trade-off versus the room you have available.

Telling us more about those factors will help others help you.

Curve radius rule-of-thumb from the Layout Design SIG.

Good luck with your layout.

 

[RR_Mel]

Hi and Welcome to the Forum!

 

For me it would depend on the size of the layout, the larger the layout the larger the radii. 

 

My layout is 14’ x 10’, my tightest radius is 18” in my yard due to space limitations.  My mainline minimum is 24” and are hidden under mountains.  My viewed mainline minimum is 28” with a maximum of 30”.

 

I have small and large locomotives from 0-6-0 to 4-8-8-2 & 2-8-8-4 steam and GP7s to E7s diesel power, all will operate through the 18” radius and #4 turnouts in my yard.  My longest cars are 72’ passenger cars but not because of tight curves, longer cars on small layouts doesn’t work for me.

 

The only problem in the 18”/#4 tight curves are my GS4 4-8-4 steam, they will clear the turnouts at a little over a creep but that is max speed in my yard anyway.

 

 

 

Mel

 

Modeling the early to mid 1950s SP in HO scale since 1951

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

 

I'm beginning to realize that aging is not for wimps.

 

 

[Colorado Ray]

I think Steve needs to make a sticky on curve radius so that newcomers don't have to start the umpteenth thread on the subject.  I mean no disrespect to the OP, who may not have any idea that this has been endlessly covered. 

Ray

[rrinker]

 Of course, what would you put in such a stickey? There are guidelines for smooth operation, there are guidelines for best appearance, and still they are at best just that - guidelines. The only way to be absolutely sure is to mock it upa nd test with the exact cars and locos you plan to run. Guidelines might say that 24" radius is enough for a 6 drive steam loco, but that nice NYC Hudson you have derails every time on anything less than 28" radius. Or the guidelines might say you need 30" minimum for your size cars to operate, but every one you have have extended couplers and work reliably even at warp speed through 24" curves.

 Guidelines give you a good starting point but what you can get away with and/or what looks good to you may be totally different. Same with center to center clearances, especially on curves. Test, test, and test again with all possible combinations before laying any track permanently and you will be sure it will work and you won't have any surprises.

 That really covers just about any physical characteristic - curve radii, turnout numbers, grades, vertical clearance, etc. Guidelines are a good place to start but you still need to test with your specific equipment because the people who come up with the guidelines can't possibly test against every product on the market. ANd because of the varuous compromises built in to most any model, you can;t just assume anything. I've seen cases where an 89 foot autorack handles the curve and clears any possible car on an inside track but an 80 foot passenger car sideswipes something on the inside track, all else being the same. That's why you need to test with a representative sampling of your rolling stock, not just assume that because the longest car works, anything shorter will automatically work.

                              --Randy

 

[Choops]

Colorado Ray

I think Steve needs to make a sticky on curve radius so that newcomers don't have to start the umpteenth thread on the subject. I mean no disrespect to the OP, who may not have any idea that this has been endlessly covered. Ray

Agreed.  Seems there are a lot of new posters lately asking these questions.

Steve

 

[Colorado Ray]

Randy, the points you raise are exactly why a sticky would be helpful.  The sticky doesn't have to have the definitive answer, it would just be a repository of the endless discussions with the same comments made time and again.  Another example of a repeated thread includes a discussion of grades.  Having a sticky would allow folks with new ideas or thoughts on the topic to add their comments there without having to start a new, and potentially redundant, thread. 

Ray

[selector]

Everyone at some time asks for advice on what is the "best" radius for curves in a given scale.  The question is only answerable by the asker.  Strange, huh? The reason is that the person asking is the only person who know what curves he needs! 

Wait a minute,...that's no help at all!

Ah, but it is.  The person asking will have his/her answer when he/she knows the answers to questions he/she ought to ask first.  Questions such as:

What scale am I using?

What types of rolling stock will need to be able to negotiate my curves?

Can I fit curves of that nature in the space I have allocated and still complete my intended track plan?

What would I need to change in my ideal and available curves if I were ever to add new rolling stock and locomotives to my stable (yes, almost all of us do add new items eventually)?  Would I need larger curves, or could I keep the same ones?

Our prior preferences in rolling stock, and then based on the era and prototype's use of rolling stock, and then again what the manufacturers offer as facsimiles of those items, determine the nature of our track plan, including the curves we'll need.  There will be a lower limit in radius until things start to go wrong.  Upward to expanding radii should present no problem or danger provided you can still shoehorn them all into the space you have, or into the same track plan if you hope to keep it.

In the end, once you decide on what you will purchase, laying smaller and smaller curves with flex track, and then testing coupled cars and locomotives through those curves, is the only sure-fire way to settle the matter.  Even stated specs from the manufacturers are sometimes iffy (ask me what I learned about the Walthers heavyweight passenger cars with their diaphragms).

Finally, if you want to err on the side of caution, add 10% to whatever lower limit in radius you find you need.  Especially if you are laying curves out by sight and not using strict measurements and centerlines.  Or, just use the broadest curves you can "afford" to lay and still have good use of the space you have to play with.

[BMMECNYC]

Here is a good starting point. 

http://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-11.pdf

[jjdamnit]

Hello all,

On my 4'x8' HO pike I use sectional track from 15-inch to 22-inch radius with a maximum grade of 3%.

The majority of my turnouts are #4, the Wye is made up of PECO #2 turnouts to an Atlas Mark IV Wye.

I DIY any flex track as needed (http://cs.trains.com/mrr/f/11/t/256138.aspx).

Because of the limitations of the trackage radii I am limited to 4-axle diesels and 0-6-0 steam. Hardly toys and satisfactory to my needs.

My coal drag is made up of vintage 34-foot operating hoppers originally produced by Tyco and upgraded with Kadee split bolster trucks and couplers.

I run a 4-unit GP40 consist with 12 coal hoppers.

My rotary plow consist does have a 54-foot flatcar which negotiates the #4 turnouts with no problem.

By all means if you have the space to model 48-inch curves great!

For those of us that want to do more with less I suggest ignore the naysayers and do what works for you.

(See my disclaimer.)

Hope this helps.

[riogrande5761]

Short answer, as big a curve radius as you can fit in the space you have.

My personal absolute minimum would be 28 inches, but I've managed to keep it at 32" on my last two layouts bu wish I could do bigger.

[hornblower]

If your layout space is restricted enough to require smaller radius curves, just use smaller locos and rolling stock to keep things looking right.  Four axle diesels, 2-6-2, 4-6-0 or smaller steamers and 40 foot or smaller freight cars look just fine on curves of 22" radius.  The shorter rolling stock tends to make the trains look longer as there are more cars in a train.  Passenger trains on such curves tend to restrict you to older era modeling where 50' coaches would be appropriate.

My own layout models a fallen flag short line built in the 1890's and so the 22" mimimun radius curves reflect a line built during an era when smaller rolling stock was the norm.  Even though my layout scenario is set in the 1950's, I also assume that development in the area along the railroad grew quickly and swallowed up any land the railroad could have used to ease it's curves.  Thus, the 1890's as-built condition of the line restricts equipment to 4 axle diesels, small steam and 40 foot or less freight cars.  Passenger service is limited to short commuter trains using hand-me-down 50' wooden coaches. It all seems to work just fine and no complaints (yet) from visiting operators.

[BMMECNYC]

jjdamnit

For those of us that want to do more with less I suggest ignore the naysayers and do what works for you.

Who was naysaying?  It seems that almost everyone said test the equipment you have/look into minimum radius specs for equipment you want to run in future.  Sounds like solid advice to me.

[IRONROOSTER]

Buy a copy of Track Planning for Realistic Operation by John Armstrong (available from Kalmbach - click shop>books on the menu bar above).  This topic and many others about planning your layout are covered.  If you only buy 1 book for this hobby, this is the one.

Good luck

Paul

[ACY Tom]

My own personal belief is that 28" is the minimum for operating full size passenger cars or 89 foot modern freight cars with body mounted couplers, as well as and most steam locos. Even so, I prefer 30" or greater. There are a few items that require more generous curves, but too not many. Most 6-axle diesels will negotiate a 24" radius, and most 4-axle diesels can manage 18". Some rather recent offerings are specifically engineered to get around very sharp curves, but they usually look horrible while they are doing it. Equipment representing an earlier era tends to be smaller, and it looks and operates better than the bigger, more modern equipment on tight curves.

Tom   

[ATLANTIC CENTRAL]

Bigger is better.........

My choices, 36" minimum mainline, 48" prefered.

Sheldon

[jjdamnit]

Hello all,

Lone Wolf and Santa Fe

Here is a list I made up of minimum radius for different type of equipment. Toys = 18” Most scale models = 22” Scale models with accurately detailed fames and coupler pockets = 24” Steam Locomotives = varies up to 30" or more.

The quote that 18-inch radii is for toys! Seems to be nay saying to me. 

Hope this helps.

[DSchmitt]

jjdamnit

Hello all,

 

 

Lone Wolf and Santa Fe

Here is a list I made up of minimum radius for different type of equipment. Toys = 18” Most scale models = 22” Scale models with accurately detailed fames and coupler pockets = 24” Steam Locomotives = varies up to 30" or more.

 

 

The quote that 18-inch radii is for toys! Seems to be nay saying to me. 

Hope this helps.

 

18" radius was the HO standard for years.  Many fine HO layouts have been built with 18" radius. Still bigger is usually better, especially with the newer locomotives and cars which often do not have the design compromizes that were accepted in "the old days".

[BMMECNYC]

jjdamnit

Hello all,

 

Lone Wolf and Santa Fe

Here is a list I made up of minimum radius for different type of equipment. Toys = 18” Most scale models = 22” Scale models with accurately detailed fames and coupler pockets = 24” Steam Locomotives = varies up to 30" or more.

 

 

The quote that 18-inch radii is for toys! Seems to be nay saying to me. 

Hope this helps.

 

Fair enough.  I use 18" radius for spurs. 

[DSchmitt]

BMMECNYC

Fair enough.  I use 18" radius for spurs. 

Good point.  Many  model railroaders make the mistake of seting a min radius for the main line and using it everywhere.  On spurs and in industrial areas the prototype may have curves that modeled in scale would make many model railroaders cringe.

 

[7j43k]

BMMECNYC

Fair enough.  I use 18" radius for spurs. 

 

 

Ah.  I see you are going with prototype curves!

 

A Baldwin 660HP diesel switcher could do 16.5" with train (presumably 40' box).  And 6.9" by itself, FWIW.

A UP SW10 could do 14.5".  That's probably without train.

A BNSF GP15 is 16.5 singly.  And 23.5 with a second unit coupled.

 

 

 

 

 

Ed

[BMMECNYC]

40' cars or less and 44ton/0-6-0s/HH660s and Alco S1s.  18" for pier tracks, other sidings between 18-22.  Largest planned radius at the moment is somewhere around 55" in one or two places.  Layout plan is being professionally critiqued.

[BMMECNYC]

Creative Layout Design, by John Armstrong covers this whole curve radius thing well.  As does Track Planning for Realistic Operation, also by John Armstrong.  The latter is in print.  The former I stumbled upon on consignment in my LHS.  Paid original cover price.  Even had the original sales slip still in it.  I should find mine and put it in there for posterity.

[ATLANTIC CENTRAL]

BMMECNYC

Creative Layout Design, by John Armstrong covers this whole curve radius thing well.  As does Track Planning for Realistic Operation, also by John Armstrong.  The latter is in print.  The former I stumbled upon on consignment in my LHS.  Paid original cover price.  Even had the original sales slip still in it.  I should find mine and put it in there for posterity.

 

Paul Mallery, another great from back in the day, had a little different take on radius than Armstrong in his Trackwork Handbook.

He lobbied for much broader curves for HO trying to represent Class I mainlines, with 48" being the desired goal for mainlines. 

A target I am getting close to with my current layout rebuild, with 36" as my minimum mainline.

Sheldon

[mbinsewi]

Well, the OP hasn't chimed in since his first post on Feb. 27.  Hopefully, he's read some of this, and decided accordingly.

Mike.

[carl425]

ATLANTIC CENTRAL

Paul Mallery, another great from back in the day, had a little different take on radius than Armstrong in his Trackwork Handbook

I'm sure you don't mean to imply that Armstrong was a proponent of tight radius curves.  This is not the case.  He was about understanding your options, how one choice impacts others, and finding the best compromise that would allow you to satisfy as many of your desires as possible while dealing with the reality of available space.

OTOH, like we have in all evdeavors where human males participate, there are those in this hobby who are always looking for the opportunity to say "mine is bigger than yours".  ...and BTW, I do not mean to identify any specific individual as a member of this group.

[Colorado Ray]

BMMECNYC

Here is a good starting point. 

http://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-11.pdf

 

We could debate this till the cow's come home.  BMMECNYC's advice is sound and rather than the starting point should be the end point.  Recommended Practice 11 very clearly indicates appropriate rolling stock for what ever radius you have.  Seems simple enough that once you know what your limiting radius is, you know what type of railroad you can model.  If there's a disconnect between what you have and what you want your choices are to either change scales or find a larger space.

Ray

[ATLANTIC CENTRAL]

carl425

 

 

ATLANTIC CENTRAL

Paul Mallery, another great from back in the day, had a little different take on radius than Armstrong in his Trackwork Handbook

 

 

I'm sure you don't mean to imply that Armstrong was a proponent of tight radius curves.  This is not the case.  He was about understanding your options, how one choice impacts others, and finding the best compromise that would allow you to satisfy as many of your desires as possible while dealing with the reality of available space.

OTOH, like we have in all evdeavors where human males participate, there are those in this hobby who are always looking for the opportunity to say "mine is bigger than yours".  ...and BTW, I do not mean to identify any specific individual as a member of this group.

 

No, it is not a criticism of Amrstrong, just pointing out that other leaders in the hobby had somewhat different opinions.

And even 50 years ago or longer, a fair number of people did understand that better operation and better appearance was acheived with larger curves.

And, it plays along with a concept I support, there is a difference between a large layout and a complex one. A layout may occupy a somewhat larger space to allow larger curves, longer yard and sidings, etc, without being anymore "trackwork intense" than a layout others would have in a smaller space.

Sheldon