# What's YOUR Min. Radius?



## Gary Woolard (Jan 2, 2008)

Or diameter, either one -- I'm not afraid to divide by two











Here's the deal -- I'm trying to design a layout that will handle the typically large radius's (radii, I know) that live steamers need. One of my favorite local steam layouts has a min radius of 8.5 feet, and it seems to handle everything up to Berks and Challengers. But I was surprised to discover that an Aster G-4 couldn't keep on the track. So I'm curious -- what's the min radius for YOUR largest engine? How wide a curve will I need if and when I invite "the Big Boys" over to play?

Thanks in advance --


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## David Leech (Dec 9, 2008)

Gary, 
With live steam, it's all to do with the length of the wheelbase. 
Typically, a live steam loco does not have the side movement that is allowed with electrics, so a large wheeled 4-8-4 will need a good 10 foot radius. 
Each of a Big Boys engines, actually has a smaller wheelbase than a Daylight, so could potentially go around a steeper radius, but then cylinders and multi wheel tenders come into the equation. 
I would try and keep above 10 foot radius, and if possible, go as large as you can fit in to the space. 
All the best, 
David Leech, Delta, Canada


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## Dr Rivet (Jan 5, 2008)

Gary 

Ten foot MINIMUM RADIUS. My minimum radius is 24 feet, but I have more space to work with than the average guy, even with a one acre lot. My layout, not including the steaming bay fits in a box about 120 x 140 feet. Part of the issue is that Asterhaulics tend to run at warp speed, so 10 foot radius slows them down... or it gets to be a heart stopping experience watching them run. I would try to use 12-15 foot radius if you have the space.


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## deltatrains (Nov 25, 2010)

Very wise advice from both of the above members. I originally had five foot radius when most of my friends had four foot radius and I thought it was good.Then along came live steam and the need for bigger engines so I had to redesign my layout inside a smallish city lot, (60 X 120 ft) and now have one track that is ten foot minimum radius. Another point to consider, if you have the room, is transitioning into those curves by starting with a larger radius than that which will be the minimum in that section of curved track. This of course will add to how much the total diameter will be than the minimum ruling radius would eventually have created.
Hope that makes sense. It is easier to build from scratch and get it correct the first time than to try and rebuild later. All the best. Peter.


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## Joe Johnson (Jan 2, 2008)

Minimum diameter is 11 feet. Largest engine AC K-37. 

While it is the smallest, the engine that is most sensitive to radius seems to be the AC 3 cylinder Shay. I had some 8' on my original layout and it certainly didn't like those curves. Although I have to admit my track laying skills were pretty meager when I laid those curves so it could have been the track crew as much as the curve diameter.


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## vsmith (Jan 2, 2008)

Minimum Diameter is 21" ....thats INCHES not FEET


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## Dave Meashey (Jan 2, 2008)

"Minimum Diameter is 21" ....thats INCHES not FEET"

I have actually seen a photo of a Cricket negotiating less than that, but this thread is really about the BIG hogs. I suppose the PRR T-1 even has a longer fixed drive wheel base than a garden-variety 4-8-4.

I hope to keep my purchases to the smaller wheel arrangements. That way I won't need a rail bender or additional curved track. I love to watch those big hogs highball, though.

Best wishes,
David Meashey


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## steamtom1 (Jan 2, 2008)

*As to your question of Min. Radius, it does depend on what you are running. Like this...*











*Or perhaps even this...*


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## bicyclexc (Mar 31, 2010)

My outdoor layout has a min radius of 4 feet on just the reversing loops, everything else is 5 feet. I thought that would be adequate, but I'm already finding that even that is too tight to make things "Look Good". Next layout will have larger turns. Maybe even scale turns, (16 degree max). 

My indoor layout radius is 1.5 feet. lol Critters only.


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## Phippsburg Eric (Jan 10, 2008)

I also had 10 foot diameter curves but am upgrading to 16.5 foot DIAMETER which is a good improvement even with smaller engines and stock, I would have gone larger yet but would have had to blast or close the driveway to do it!


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## Kovacjr (Jan 2, 2008)

I'm stuck with about 9.5' radius on one end of my track as it stuck between my house and the fence. The rest is all 10' Radius. Would of gone bigger but don't have the yard to do it. Mine is a L shape covering about 70' x 100'


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## Dr Rivet (Jan 5, 2008)

Jason 
Don't try to get an Accucraft GS-4 around that tight curve... never happen.


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## David Leech (Dec 9, 2008)

Posted By bicyclexc on 05 Dec 2013 05:39 AM 
My outdoor layout has a min radius of 4 feet on just the reversing loops, everything else is 5 feet. I thought that would be adequate, but I'm already finding that even that is too tight to make things "Look Good". Next layout will have larger turns. Maybe even scale turns, (16 degree max). 

My indoor layout radius is 1.5 feet. lol Critters only. 


I believe that a 16 degree turns is about 11 foot radius.
Hardly scale if you are talking mainline!
All the best,
David Leech, Delta, Canada


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## Charles (Jan 2, 2008)

If one has the room bigger is always better. Not only for locomotives but the look of the train. At minimum 12 foot would be fine. All depends on layout design, space and any future engine requirements.


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## Dan Pantages (Jan 2, 2008)

1/1 Southern Pacific Railroad's ruling radius scales down to 66ft radius in 1/32 scale.


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## Chris Scott (Jan 2, 2008)

Posted By Joe Johnson on 04 Dec 2013 06:22 AM
Minimum diameter is 11 feet. Largest engine AC K-37.

While it is the smallest, the engine that is most sensitive to radius seems to be the AC 3 cylinder Shay. I had some 8' on my original layout and it certainly didn't like those curves. Although I have to admit my track laying skills were pretty meager when I laid those curves so it could have been the track crew as much as the curve diameter.

My AC 3 Cylinder Shay on my ~ 4.5' R layout pretty well. Although she was temperamental about whether the cylinders were on the inside rail or outside rail. Years since that layout so I'm not certain, I believe the Shay balked a bit if the cylinders were on the inside rail because the u-joint linkage would bind. I thought of cutting a little off the male expansion link so it would compress a little more but never got around to it.


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## Randy Stone (Jan 2, 2008)

While I'm not into steam, I hope my experience helps everyone avoid the problems I have experienced do to my choice of switches. I have a layout running inside my 2 stall garage. I used 8 ft dia. curves for the main line. I also used 4 Aristo Craft Wide Turnouts (10 ft dia turnout Switches) to access two frt yards and an industrial siding. But, the problem came when I used 4 ft dia switches inside the frt yards. Originally I was installing truck mounted Kadees on everything. but then I started installing body mount Kadees and that is when the problems started. They worked fine on the short cars but when I tried backing a frt consist with a long gondola that had the body mount couplers through a 4 ft switch the car would keep derailing. So, even though the 4 ft dia curve of the switch is a short length, it's still long and tight enough to cause problems with long cars and locos. 
I bet there are sidings on real railroads where long cars are prohibited due to sharp radius curves being used to reach a customer.


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## Chris Scott (Jan 2, 2008)

Posted By Dan Pantages on 05 Dec 2013 09:24 PM 
1/1 Southern Pacific Railroad's ruling radius scales down to 66ft radius in 1/32 scale. 
In real terms that works out to about 2.5 degrees and and half a mile. 

Jim;
You're going to have to enlarge your layout.


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## Reg Stocking (Sep 29, 2010)

Years ago I read somewhere that the minimum radius on the original narrow gauge Rio Grande line from Denver to Salt Lake City was 205 feet. In Fn3 this comes out almost exactly 10 feet. This is lovely if you have the room. 

Also years ago I had a mentor who custom-built O scale locomotives and passenger cars. He gave me some rules about aesthetics. If you can see the outside rail from above when a passenger car is on a curve, the curve is too sharp. For full-length cars in American O scale (1:48), the minimum radius was 6 feet. In 1:32 this would be 9 feet. Anyone have thoughts on this?


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## Chris Scott (Jan 2, 2008)

Second thoughts. Check back later.


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## bicyclexc (Mar 31, 2010)

The tightest curve on the Western Maryland Scenic Railroad for example is 19 degrees. It is located on track 1 in Frostburg MD going into the turntable. That works out to a real-life 302ft radius, and about a scale 10ft radius. 

The WM main line is more often about 6 degrees, which works out to a 955ft real-life radius and about 30 ft scale radius. I hope that my next layout can more or less abide by those upper and lower bounds.


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## Randy Stone (Jan 2, 2008)

Posted By bicyclexc on 07 Dec 2013 06:48 AM
The tightest curve on the Western Maryland Scenic Railroad for example is 19 degrees. It is located on track 1 in Frostburg MD going into the turntable. That works out to a real-life 302ft radius, and about a scale 10ft radius.

The WM main line is more often about 6 degrees, which works out to a 955ft real-life radius and about 30 ft scale radius. I hope that my next layout can more or less abide by those upper and lower bounds.

Thanks for the comparison. I've always wondered just how our radius turns compared to the prototype. So, our 20 ft diameter curves are still quite sharp/tight compared to most standard gauge mainlines. The our 20 foot dia curves are probably more inline to what can be found on narrow gauge railroads.


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## BigRedOne (Dec 13, 2012)

My employer receives material by rail. The track to our property forms a "U" of slightly more than 180 degrees; using Google map, the diameter of the curve is 276 meters. That works out to 8.625 meter diameter in 1:32 scale, or over 14' radius - and this is a small switching siding. 

The tight turn puts a lot of stress on the track, which sends the gauge out of alignment. 

The "Altoona Curve" of the former PRR scales to 20.3 feet radius in 1:32 scale.


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## Chris Scott (Jan 2, 2008)

Posted By Reg Stocking on 06 Dec 2013 11:59 AM 
Years ago I read somewhere that the minimum radius on the original narrow gauge Rio Grande line from Denver to Salt Lake City was 205 feet. In Fn3 this comes out almost exactly 10 feet. This is lovely if you have the room. 

Also years ago I had a mentor who custom-built O scale locomotives and passenger cars. He gave me some rules about aesthetics. If you can see the outside rail from above when a passenger car is on a curve, the curve is too sharp. For full-length cars in American O scale (1:48), the minimum radius was 6 feet. In 1:32 this would be 9 feet. Anyone have thoughts on this? 
Per Narrow Gauge Railroad Discussion Forum:

Posted by: Earl (IP Logged)
Date: September 10, 2010 09:35AM

"Sharpest curves on the D&RGW ng was 24 degrees. There was one mainline curve west of Monero at 24 degrees. The Chama-Alamosa line's maximum is 20 degrees. The Silverton Branch has several 24 degree curves. Wyes were laid out with a 24 degree maximum. The track profile I have dates from 1954 and doesn't show Marshall Pass, but I think there were some 24 degree curves up there too. The Baldwin spec sheet for 480's show a maximum curvature in road service of 24 degrees (at 25mph with a 6" super elevation!) with an "emergency" curvature of 30 degrees. I recall when the D&S started running 481 there was a tendency for the inside pilot truck wheel to lift off the rail on some of the 24 degree curves, so to get around a 30 degree curve, it would have to be REALLY good track. "

Per Stan's Handy Converter for Model Railroads, Version 16.0.0


1:1 Curvature (degrees) => Scale Radius
Degrees = Prototype 1:1 (100') = 1:20.3 = 1:32 
19 degrees = 303" = 15' 0" = 9' 6"
20 degrees = 288' = 14' 2" = 9' 0"
24 degrees = 240' 6" = 11' 11" = 7' 6"
30 degrees = 193' 2" = 9' 6" = 6' 0"


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## Kovacjr (Jan 2, 2008)

Even the Unitah scaled out to about 9' radius I think it was when I was looking into a 2-6-6-2


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## cocobear1313 (Apr 27, 2012)

My old track had a diameter of 13 feet. I will have 20 foot diameter curves minnimum when I put my new one in. The exact scope is still being negotiated with the missus. 

Dave


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## SD90WLMT (Feb 16, 2010)

Ya all know I'm at the other end of the spectrum...ha!! 

Put for conversation here, since it has turned to prototypical sizes.... 

On my Fn3 I have some of these... 

17ft. R = 345' R 
15ft. R = 304.5' R 
40ft. R = 812' R 

And for the 1/29th crowd.... 

Mainline minimum.... 
45ft. R = 1305' 
....others include... 
50ft. R = 1450' R 
55ft. R = 1595' R 
60ft. R = 1740' R 
75ft. R = 2175' R 
100ft. R = 2900' R 

I foresee some curves on sidings being as tight as 10-12' R, while most will be more in the 13'-18' R ranges.. 
These may require a smaller road switcher or local engine to spot cars, from and to a place they can be reached by a thru freight. 

Dirk - DMRR & DMS Ry. 
Running on the Lordsburg sub, UPRR


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## Chris Scott (Jan 2, 2008)

I have 2 acres of wonderfully flat land that used to be vineyard; 165' x 545'. So I was planning on an 80' radius by 270' radius layout. One lift gate at the driveway entrance. I call it my irrational curvature layout.









A few things come to mind contemplating my future layout and those above;

I think we've reached the point of diminishing returns.









It's not how big it is it's how you use it.









Bigger is not always better.









Better always seems bigger.









This is an arms race in layout size.









Someone's layout somewhere will always be bigger than yours.









Rationally, what size layout triggers conversion to a larger scale & gauge ?











Just sayin'


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## BigRedOne (Dec 13, 2012)

I'd see the "sweet spot" of radius to be that which is visually a reasonable match to the prototype being modeled. Large mainline locomotives and cars look so much better (to me) on sweeping, wide radius turns. Having every curve the radius representative of the absolute minimum a train at low speed can negotiate, by a model running at mainline speed, looks silly. 

The upper limit would be the point at which I can't see the train from one end of the railway to the other. 

About 12 foot is the largest I can comfortably fit in my back yard, retaining walking / mowing access to both sides, though I expect to start with shorter narrow gauge prototypes.


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## Gary Woolard (Jan 2, 2008)

Thanks, Guys, for all your help. (And it got into an interesting discussion of prototype practice







) My main focus was an attempt to figure out if I might attempt a tighter curve for a live steam radius than the 9' minimum I've got already (and most of the curves are 10'). Looks like I'd be courting trouble to try 8'6", so I'll stick with what I've got.

I'm actually designing two loops, roughly, one above the other but staggered on a slope (think of a wedding cake that's slipped over. I'm trying to connect the two with a 'transition' track that achieves a 24" rise with a resultant 2% grade. So, dsince somebody has already posted a question about a 10% grade (whew!) I'll head over there and ask y'all what you think of a 2% grade!


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## jjwtrainman (Mar 11, 2011)

For my next indoor layout in 1:20.3 I plan to use 4 foot radius, which is 8ft diameter. Why? First, all of the locomotives I plan to accumulate aren't that large. Second, it's inside so I can't go much larger. However I should note that both of my current locomotives are 0-4-0 type, but late on I may go up to something like a 2-6-0. 

For what you're doing outside, the general idea is to have a large of radius as possible, or practically possible. The one problem with this idea is that if I had a 20' by 20' space, I would then have a 10' radius curve to make a large circle. But if you are only running smaller locomotives, that large of a radius is unnecessary. 

So what to do? For me it is about finding a happy medium that is both adequate for the locomotives but doesn't eat up too much space. Obviously what works for you depends on you situation. If you like running live steam, it would be wise to have a large radius so that the engines don't encounter too much resistance and hinder their performance. 

For what you do for radius will depend completely on what you run. If wanting big boys on the layout, I can imagine it would be pretty big though  

Best of luck! 

--James


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## du-bousquetaire (Feb 14, 2011)

Radius isn't the only aspect of track planning for instance there is also switch angle or size I use exclusively N°8 points or over because we europeans run engines and cars with buffers, under that size you will have buffer lock on the reverse curve. A minimum radius often found on engine terminal trackageand on wyes or interchange tracks on prototype railroads is around 11'6" radius, as John Armstrong used to explain in Model Railroader magazine, every engine or just about, can negociate that at very restricted speeds. My Accucraft T1, which is probably the longest rigid wheelbase engine you can find, negociates that. The beauty of Johns philosophy is that if real engines pass through those kinds of curves, gingerly, because the side play in real engines is practically identical to the one in our models (that is: not scaled down) and there aren't the dynamic forces that come into play with real size locos, ours can negociate these types of curves at cruizing speed. This is real good news to us modelers. however I can confirm from more than 30 years of operation in the garden, these kinds of curves do offer a big rolling resistance to the train. So bigger is adviseable. Also another important factor to consider in layout planning is the size of your sidings and yards. As long as I was modeling continental trains, an 8-9 meters siding was a going proposition, I could fit a7 coach passenger train in it when most pacifics handled 8 and about 25 continental size freight cars. Going american (and Pennsy to boot) means 40', 50' up to 70' freight cars and up to hundreds of them. Suddenly my siding looked ridiculously short... On the other hand I confirm that one has to keep things in reason very large layouts means that your train starts to look like N gauge once they are far away. And depending on your climate the maintenance can easely get out of hands. my track is about 50 meters in circumference. Because of my US modeling, I am contemplating replacing the 11'6" curve by one of17'6" radius which should lengthen the main to around 60 or so meters. But I will also lengthen a siding considerably. The larger the curve and the pointwork the smoother the operation and the better trains look, this is the most important factor for me. When I look at some videos of GG 1 or big boys going over some 4foot cuves it makes me sick. These weren't rapid transit equipment at all. So why have them run on rapid transit type of right of way? If you must use that type of curves go narrow gauge or Rapid transit. Especially out of doors. I mean that, after years of beying limited by the size of indoor space available to my hobby, coming out of doors was like discovering freedom after years in jail. There are limitations out of doors also, my terrain for instance is on an average ten percent gradient: Too steep to climb. But I took advantage of that to have the track at ground level on one side and at table top height on the other. Great for manual controling of our steamers, on the fly. Think and plan carefully, you will be happier on the long run.


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