From the archives...

Dear ???

Suggest a read of one of the earliest articles published in MRH...

http://model-railroad-hobbyist.com/mrh2009-01/curve_insights

I'd also ask, what scale are we talking?
(A little confused about the "30-40 cars = 30ft long train" calc...)

Happy Modelling,
Aim to Improve,
Prof Klyzlr 

My initial thoughts were for

I'd go with as wide of curves as possible if appropriate based on the prototype you are modeling( is it a straight railroad or a curvy railroad or location?). Curves are not a waste of space if the modeled line was curvy, in that case they are more realistic than straights. My last O scale layout had 46 inch radius mainline and if I build my new  layout in S scale it will also have 46 inch radius or if I build in HO scale about 42 inch radius. The HO trains look a lot better on 42 inch than the O trains did on 46 inch. My small N scale layout has 19 inch which is also pretty decent looking.....DaveB

Our club has curves that were

Our club has curves that were initially set at 30 inch radius HO scale. However the temptation by some of the original builders to short change this from time to time has resulted in some that were sharper. I know of some 28 inch curves and there might just be some 26 inch curves.

Now I would ask what type of equipment you are planning, if I remember from other posts it is diesel locos. The longer the equipment the better it looks on bigger curves. After running my equipment 1950s era, nothing over 85 feet in length I would agree with the 42 inch radius as a minimum. Articulated steam looks better on bigger curves and should you ever get the urge to move your era or time period back you will enjoy it. If you don't your existing equipment will look better and run better on the bigger curves.

With that said all things are a compromise and if you only have space for 30 inch radius build your layout and realize that it will not look as good as it could with the bigger curve but you might get much more railroad in the space you have.

I believe that one of the best calculators for radius was based on length of equipment. I also think it involved the length of your equipment times a number between three and five with the higher number producing the best result. I believe this should be credited to Joe Fugate as I believe I am quoting one of his posts. Example HO scale 85 foot car is close enough to an actual foot to use that. Three times that will give us a 36 inch radius, four times is 48 inches and five times is 60 inches. Now if for example you were going to an earlier time when your longest car would be say 8 inches long you would be looking at radii of 24 inches, 32 inches, and 40 inches respectively.

Generally the biggest curves you can fit will be the most reliable and best looking. You can also use sharper curves once you leave the mainline and go to industrial tracks as you will be using smaller cuts of cars and engines generally to perform switching operations.

Yes, check MRH issue 1

The Bigger, The Better

If space is not an issue, make the curves as large as possible, it's more realistic, more pleasing to run on, operates better, and just plain amazing!

My largest curve has a 61.6" radius and it's fantastic to watch trains on it.

All, Thanks for the link to

All,

Thanks for the link to the radius info. I am modeling HO and will be using up to 85 foot cars and 6 axle locos. I like the math on lent of car times 3, 4 and 5. My thoughts are in the 36 inch area. But needed some validation. 

Thanks again 

Mike

85 footers in HO

Viewing angle has a big part

Viewing angle has a big part in how toylike your curves make your equipment appear too.  From eye level a sharper curve isn't as noticeable.  

Auto racks on 36" curve coming out of staging. 

My main line is 40" curves because I have the space, but you get the idea about viewing angle. 

Viewing angle and inside a curve

Viewing angle is a good point - you can get away with a lot if the layout is near eye level when it comes to selective compression. I have some cases where bridge abutments are narrower on the back half as compared to the front half - and because it's near eye level, you don't notice it.

The other thing that's true about your photo is you're viewing the curve from the inside - curves always look less sharp when viewed from the inside. Knowing this is a trick you can use if you're really pressed for space - find a curve where you view it from the inside on your layout and drop the radius a few inches. As long as it's 3x of your equipment length, things will run fine on it - and viewing it from the inside will make it look less sharp.

You can also get away with a

You can also get away with a tighter radius if you broaden the transition from curve to straight track, I forget the term used to describe it I think its "easement" but if your arc is say 30 inch radius,  increase that radius to 36 inch  as you ease into 30 inch over all radius..

WOW! Great explanations from

WOW! Great explanations from all...  I see my "blobs" need to be larger but inside radii can be tighter if needed. Love the visual too. (and the Grande at the point!).

I wanted my curves to be as

I wanted my curves to be as broad as possible. I am in HO scale and ended up with a 32 inch minimum radius, but this is only one curve on the mainline. Most curves are 38 to 42 inches.

Even in industrial areas my minimum is at least 20 inches. Even a string of 40 box cars look a bit toy like on an eighteen inch radius. I also like to run passenger cars and they look so much better on broad curves.

I have to say, the first

I have to say, the first article from Joe's very first issue of MRH magazine is possibly one of the most valuable layout design pieces of information that I've come accross.

As he says, with this information at hand, you know what you're getting into, and why.  I am working on some layout design stuff, and that information is right there, in my face.  No denying it.  No, "well, 28" sounds large..." (when I want to run HO scale autoracks, and have them look good AND be able to couple / uncouple on curves).  I can't have my cake and eat it too.

I think this info could be used to really help people determine a scale, as much as anything else.

My layout is located in a

My layout is located in a long 12.5' wide room. I made the curve to turn 180-degrees with a 54" radius. Nothing technical. Nothing complicated. This is the min radius on the layout. Trains work very well around these somewhat broad radius turns. To be honest, I did not pre-determine the radius. I fit the track into the space I had to make the turn and it just ended up being 54" radius. My feeling is that too many model railroaders over-complicate things when it is not necessary.

3x gives you the minimum for

Dreams vs. reality for most of us.  Unless we are fortunate enough to have a large basement, most of us have to be content with less than 40-inch curves - so toy-like is something we are stuck with save a few John Armstrong cosmetic curves.  I put one into my tiny 10x18 layout but curve minimums are a tight 32-inches.

I do struggle to impress upon noob's on other forums, such as MR, that they need to break away from the 18 and 22 inch curve model that continues to plague the hobby from ancient times.  Such tight curves restrict people from running much rolling stock and if you think 36-inches looks horrible under long cars, 18 and 22 inches is nightmarish or impossible, yet many a large percentage start there and I have to gently encourage them to think a little broader - and for them I think realistic is 24 inches or maybe 28.

I totally agree about how cars look on curves.  I designed in 32-inch minimum curves which should allow me to run most modern commercial rolling stock, but 89' TOFC cars still don't look so hot on them.  What's a guy to do?

For me, my rolling stock and

For me, my rolling stock and my requirement to have reasonably realistic scenes for taking photos are the two determinants.  For example, all of my non-brass locos can take curves in the 24" range with ease, including at silly speeds. However, my one brass engine, a Sunset 2-10-4, requires a minimum of 30".  So say the importers. I have never challenged that figure, but since my track-laying skills are less than stellar, I figure a 10% fudge factor is in order.  Therefore, I lay, as a minimum in consideration of that one engine, 33" curves.  Obviously everything else I run will be just fine, and even shoving Walthers heavyweights won't be a problem.

For photography, I have to have several very wide curves in the 50"-and-up range.  The only way I can do that in my confined space is to place myself inside the loop and use the corners of the room for large sweeping curves.  Hence my decision, for the second time, to build a central operating pit and to have the scenery surround me and the trains doing a folded loop around me as well.

Minimum AND reality.

By design we have to have a minimum radi for curves in the design phase. In HO, 30 seems to be what most use.

One thing Ive noticed that people seem to forget, the minimum is what is needed in certain locations BUT go larger at any opportunity. Too many times you will see the same radi on every curve. Maybe a hold over from the sectional track days, but now with the flex, go large!