Turn Radius

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wheeler1963

Aurora & Portland Owner
#2
Depends a lot of what type engine and equipment you'll be running. A Big-Boy or DD40X is gonna need a lot of room. A small switcher doesn't need much. 24" is used as a good standard now days.
 
#3
Obviously, the greater the radius of the turn the easier time you will have with engines and rolling stock negotiating the curve. The problem is that most folks, including yours truly don't have the room for very large radius curves. (In point of fact, model railroad curve radii don't come close to prototype curves except for very tight branch lines or logging railroads!)

"Standard" HO scale sectional track commonly comes in 18-inch, 22-inch, and even 15-inch curves. Flex-track can, of course, be bent to form whatever curve you want. But it is somewhat more difficult to keep a consistant radius. You can obtain larger radius sectional track made by Shinohara, which IIRC, you can obtain through Walthers. In my own instance, because I want to run passenger trains, I had to compromise by using 20-inch radius Shinohara on my main lines and 18-inch Atlas snap track for tighter curves. Shinohara makes sectional track in sizes from 16-inch to 30-odd inches.
 

Selector

Active Member
#5
So if I did a 4'x8' layout, using the 22" radius would that work for a turn?
We don't know. As the first reply stated, it depends. If you run a long modern diesel, some will negotiate an 18" radius while some won't. So, you need to match your locomotive and longest pair of cars with the smallest curve that rolling combo will take.

A safe bet for almost all non-brass locomotives is 22" radius in HO. However, not all of them will work on that small a radius. A 2-10-4 steamer won't, plastic or brass, and the example of a DDX-40 probably won't either. Neither will any HO passenger car longer than about 75 scale feet that also has diaphragms.
 

tooter

play every day
#6
What's the recommended turn radius for HO scale? Looking to design a shelf layout and hopin to get a lower deck system.
If you want a continuously running shelf layout, you can run small 4 wheeled engines and short rolling stock which can negotiate very small curves. This is a test layout with a 6 inch radius circle...

[YOUTUBE]wR7LLFAj4DY[/YOUTUBE]

It is possible to fit a continuously running HO gauge oval track layout onto a shelf with a depth of only16 inches. ;)

Greg
 
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#7
A 24" radius will run almost anything...a 22" might have some difficulty with 80'+ equipment, like long passenger and intermodal cars. If you're only having boxcars and whatnot with 4 and small 6 axle power, 22" would work. I've designed my N scale railway to have 18" curves, that will run anything - equivalent to about 36" in HO.
 
#8
It depends on your layout...

If you want to run centerbeams, autoracks, 89' flats, or any really long car down your track, you want a 24" radius.

I am designing a switching layout which at minimum is 22" (mainly 24). It can take the above, but the mainline's biggest car is a Tri-Rail Bombardier Car which may be a bit tight.

Though I am not running Tri-Rail, if I really wanted, I would probably need a larger radius.

But if you're doing like a coal layout then you can get away with 22".
 
#9
It really depends on what you want to run. THe more modern the locos and RR cars are, the larger radius you will need.

If you are going to run small steam or GP-anything and some SD-somethings {up to SD-50}, you can get away with 18"R curves.

Bigger than that and you will really need bigger radii. THat would include passenger cars over 65-ish scale feet long in HO as well.

Atlas has come out with new "snap switches" that have 22"R divergent routes so you COULD, on a "plywood prairie" have an outside 24"R curve oval and switches matching into an inner circle/oval of 22"R curves IF you have an external support system for your table {such as the 4x8 recessed into a 2x4 framework}, making it bigger than just 48" wide, allowing for clearance as the locos go around, OR if you do a 5'x9' "Plywood prairie they will easily fit.

Even then, the larger steamers and modern longer diesels and longer RR cars {such as auto racks, deep well intermodals and anything over 65 scale feet} still may not like your 22"R and 24"R curves.
 
B

BSVRR

Guest
#11
you can still go with a shelf system and use gussets on the curves, maybe even incorprate some kind of down lighting in the gussets.
 
#12
I have a very limited space in which to build my layout, roughly 9' X 11'. The space is closed on three sides, so I was pretty much restricted to a U-shaped arrangement. To get maximum use of the space, I decided to go with two levels, with a helix connecting them. I would have loved to go 24" or larger radius, but it just didn't work. Instead, I used 22" radius on the helix, and 24-26 everywhere else.

I was surprised to find that I could run almost anything on that, including a Broadway GS-4. The only problem was the overhang of the loco hits the vertical spacers on the helix. I'm going to re-work those by moving the vertical supports outboard of the sub-roadbed, and I should then be able to run that engine all the way up and down the helix without hitting anything. I've also run an SD70ACe and a couple other 6-axle diesels on it without trouble.

The one thing that doesn't work, though, is just how silly those large engines look on a tight radius. They have a very 'toy-train' appearance to them, so I will stick with my original plan of only running 40' freight cars and B+B diesels. I will only roll out the big iron for special occasions.
 
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#13
Some really good information in this thread.

I generally recommend 21 5/8" to 22" as a minimum curve radius to accommodate most HO locomotives and rolling stock. You can get by with 18" to 19 1/4" radius curves if the locomotives and rolling stock are relatively short in length. Generally, the wider the radius the better but sometimes tighter radius curves are needed to fit a layout in a certain space.

One good way to avoid the unrealistic look of using tight radius curves with long locomotives and rolling, is to cover the tight radius curves with tunnels. This works especially good with tight radius turn around loops.

Best regards,
Brian
 

Wojo

Retired Engineer
#14
For what it's worth, I'm currently running a home layout with an outer loop of 26" radius, and an inner loop of 24". The curves have easements leading into them, and have a slight superelevation. I have no problem running Walthers P2K E units and passenger cars right out of the box on either curve. All main line switches are at minimum #6 frog.

I do not have a problem with 6 axel diesels either. Of course, the longer passenger cars would look better on broader curves such as 36" radius, but I do not have the room, so my regular passenger cars are PRR MP54s, prototypically correct at 62'.
 
#15
There are two different answers to the question of minimum radius depending on where you are coming from. "What will my trains get round?" and "What looks right to me?" There are some good answers already given to set you off in the right direction but try to answer the two questions for yourself by arranging a test piece.

Good idea above to hide sharp curves in tunnels, but also consider other ideas such as cuttings, buildings, etc. appropriate to the area modeled. Your 22" radius semi-circle could be 18" at the back (hidden/staging) and 26" at the front (visible).

Can I offer some words of caution.

Beware of bending flexible track too tightly. It can suffer from an effect known as gauge narrowing. This is where the ties will twist slightly (due to the webbing connection between them) so that they are no longer perpendicular to the rails. This may cause tight spots with larger locomotives. The simple solution is to use set track for the tighter curves and flexible track for curves above those radii. (The more advanced solution is to build your own track!)

Uncoupling magnets and curves don't mix.

Beware of stopping double-stack trains with loose containers on super-elevated curves.
 

tooter

play every day
#17
Can I offer some words of caution.

Beware of bending flexible track too tightly...
You can convert Atlas Flex Track into Atlas Snap Track down to a 6 inch radius with no gauge binding by first sliding out the free rail, prebending it, sliding it back in again, trimming the rails square, and adding Snap Track connector ties on each end...:)







None of these tracks are pinned down to hold their curvature. They are all laying on the table just like Snap Track. The two radii shown are 12 inches and 6 inches.

Greg
 
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#19
There is no disagreement about being able to bend flexible track down to tight radii, so long as you use the appropriately sized trains such as trolleys and the short wheelbase stock shown in the photos above. Some industrial railways and tramways are like this in real life.

What I did say was this may be a problem with larger locomotives, implying that a (border-line, hypothetical) larger locomotive my find it easier to get around an 18" set track curve than flexible track bent to 18" radius. Take another look at the photo with the graduated square. If the ties were not twisted, they would all be pointing at the corner of the square. I'm not saying that it is wrong or doesn't work, just pointing out possibilities for fine-tuning. The rustic track is probably more realistic for some industrial models!
 
#20
There is no disagreement about being able to bend flexible track down to tight radii, so long as you use the appropriately sized trains such as trolleys and the short wheelbase stock shown in the photos above. Some industrial railways and tramways are like this in real life.

What I did say was this may be a problem with larger locomotives, implying that a (border-line, hypothetical) larger locomotive my find it easier to get around an 18" set track curve than flexible track bent to 18" radius. Take another look at the photo with the graduated square. If the ties were not twisted, they would all be pointing at the corner of the square. I'm not saying that it is wrong or doesn't work, just pointing out possibilities for fine-tuning. The rustic track is probably more realistic for some industrial models!
 



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