# Minimum radius: 11” Recommended radius: 15”



## matisw (Jan 27, 2019)

Looking to buy this 

Athearn - N 4-6-6-4 w/DCC & Sound Coal Tender, NP #5138 - 22930 - *Minimum radius: 11” Recommended radius: 15”*

I have a 12" radius, how do y'all think this big Athearn will manage on a 12" inch radius, just barely, or ok?

Thanks.


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## CV-62 (Dec 9, 2018)

matisw said:


> Looking to buy this
> 
> Athearn - N 4-6-6-4 w/DCC & Sound Coal Tender, NP #5138 - 22930 - *Minimum radius: 11” Recommended radius: 15”*
> 
> ...


I am currently in the design stage of my N Scale layout. I am a model train novice, but I do my homework. I studied NMRA guidelines for various prime movers and rolling stock. These are the minimum turn radii I have entered into my book for reference. A few short months ago I could not even spell DCC. 

12-15" minumum for 4 axle diesels and 40 foot rolling stock.
15-18" minumum for 6 axle diesels, medium sized steam and 60 foot passenger cars.
20-24" minimum for big steam, modern freight and 85 foot passenger cars. 

These numbers go hand in hard with what the NMRA recommends for trouble free operation and a professional looking layout 

My layout will be Central Vermont RR transition era mid 1950's with the mainline at 19.5" radius and the short line granite hauling railroad basically 15" with maybe a 12" in the quarry area. I plan on running RS-3's and Geep GP-9's on the main line and GE 44 tonner and ALCO S2's on the short line. All period correct with the timeline of each railroad. 

Another thing to consider and you did not mention it is the size of your turnouts. That Challenger clone is not gonna like #4 turnouts and frogs. 

That loco looks similar to a UP Challenger. I would redo those specs and say 18" is the minimum to avoid potential issues. I would be surprised if it ran well and looked good on 12 radius turns. Sorry.


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## CV-62 (Dec 9, 2018)

Read and study. This should explain a lot. I downloaded the .pdf and saved it is my reference book. Remember these are all MIMIMUM curvatures. 


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


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## CTValleyRR (Jul 26, 2014)

Well, there is no substitute for a real-world test. If you can get one from someone who will take a return if it doesn't work, then test it.

Otherwise, my money would be on "don't risk it". Even if you can coax the loco around curves by itself, once you couple something to it, the tender and / or following cars may have a tendency to pull off the rails.


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## timlange3 (Jan 16, 2013)

An easement may also be a solution. Start your bend with a 15" radius and tighten to 12" after 45 degrees of curvature.


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## traction fan (Oct 5, 2014)

*"Minimum" radii Been there Done that!*



matisw said:


> Looking to buy this
> 
> Athearn - N 4-6-6-4 w/DCC & Sound Coal Tender, NP #5138 - 22930 - *Minimum radius: 11” Recommended radius: 15”*
> 
> ...


matisw;

I second CTValley's recommendation of real world testing. Here's why.

I built 12 radius curves into my N-scale layout. My thinking was "Most N-scale locos are able to get through a 9-3/4" radius curve. Anything that won't do 9-3/4 can use 11" radius right? So I'll use 12" for my minimum and that should be OK for any N-scale locomotive right?" Right, until I bought two Kato N-scale, 2-8-2 mikado steamers. They were recommended for a minimum radius of 11"; just like your 4-6-6-4 Challenger. Well they could get through my 12" radius curves---- sometimes. 
However, they tended to derail a lot more often than I was willing to put up with. I checked the gauge of both mikados, and of my track, with an NMRA standards gauge. Both were correct

So, I took some flex track, and bent it to gradually bigger radii, until I could run the Mikados forward and backward, without derailments. I found that 16" was the minimum RELIABLE radius. The smallest where those engines stayed on the track reliably. 
I ended up tearing out the 12" curves and replacing them with 16" curves
 So, I recommend you do the same thing before committing to a 12" radius. Don't take a manufacture's minimum recommendation as gospel. Test the loco on various curves extensively before settling on a minimum radius. Model locomotives are designed to handle tight curves that their prototypes would never even try to handle, but even model locomotives have their limits.

good luck;

Traction Fan:smilie_daumenpos:


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## CV-62 (Dec 9, 2018)

traction fan said:


> matisw;
> 
> I second CTValley's recommendation of real world testing. Here's why.
> 
> ...


TF, I wonder if the rear set of 6 wheels on the Athearn Challenger articulate as well as the front set? That would help on tighter curves a bit, but if not, don't you think that long loco would still have some trouble at 16"? I do not know, but I sure would enjoy testing one and finding out. Those are a beautiful locomotive and well above my pay grade.

As with computer software, always ignore the manufacturers minimum requirements and run with the recommended requirements as the minimum, at least. Safer that way.


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## traction fan (Oct 5, 2014)

*Probably*



CV-62 said:


> TF, I wonder if the rear set of 6 wheels on the Athearn Challenger articulate as well as the front set? That would help on tighter curves a bit, but if not, don't you think that long loco would still have some trouble at 16"? I do not know, but I sure would enjoy testing one and finding out. Those are a beautiful locomotive and well above my pay grade.
> 
> As with computer software, always ignore the manufacturers minimum requirements and run with the recommended requirements as the minimum, at least. Safer that way.


 CV-62;

Yes, that is the normal design for models of articulated steam locomotives. Because our model curves, even what a modeler would call a broad curve, are very much tighter than prototype curves, both the front and rear sets of wheels pivot. They typically pivot a lot further than a real locomotive's sets of wheels did, for the same reason. 

Just to illustrate how tight our model curves are, compared to the real thing, here's an example.
Prototype curves are measured in degrees of curvature, not radius. My former N-scale club, had a main line minimum radius curve of 24". If scaled up to full size, that would be a ten degree curve. The prototype would consider that an extremely tight curve! Larger equipment would not be allowed on such a "hairpin bend" for fear of binding, damaging the track, or derailing. 

regards;

Traction Fan:smilie_daumenpos:


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## Magic (Jan 28, 2014)

tf not to derail this thread too much but how do the real RRs figure a curve?
10 degrees or 15 degrees?

Magic


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## matisw (Jan 27, 2019)

Thanks, you really saved my rear end on this one! I was about to plop down about $375 for one of these with DCC/Sound installed, etc.

Ok, I am looking for a Kato (or Athearn?) Steam locomotive that can easily navigate a 12 inch radius.

I like Kato products, but I find their website less than intuitive. 

Can anyone out there recommend a specific model?

Would love with DCC/Sound installed.

Thanks.


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## traction fan (Oct 5, 2014)

*Small steam*



matisw said:


> Thanks, you really saved my rear end on this one! I was about to plop down about $375 for one of these with DCC/Sound installed, etc.
> 
> Ok, I am looking for a Kato (or Athearn?) Steam locomotive that can easily navigate a 12 inch radius.
> 
> ...


matisw;

I like Kato too, a lot. Unfortunately, while they make lots of diesels, they don't make much steam. What few steam locomotives they do make are in the mid to large range, I don't think Kato makes a small steam locomotive. In fact the only two I know of that are available now are the 2-8-2 Mikado that made me rip out my 12" curves and replace them with 16" radius, and the even bigger 4-8-4 northern. Long ago, Kato made a J3a 4-6-4 Hudson that was imported and sold by ConCor.
It was a very smooth runner for it's time, but not up to today's higher standards. It's a shame Kato doesn't make more steam since the few they do make are superb running locomotives.

I do have a little Roundhouse 2-8-0 Consolidation that runs very well. That might work for you.

Bachman probably offers more choices of steam locomotive types than any other manufacturer. I have never owned a new production steamer, since I was pretty well put off Bachman permanently by their early crap. Many like the new design Bachmans though, so I'll let them comment. 

You are definitely limiting your choices, not only in locomotives, but also in cars, with your 12" radius curves. I recommend you adopt 16" as a minimum radius as I have. The Mikados work just fine on these broader curves. It may mean ripping out track, or even re-designing your railroad a bit, but In the long run, it was worth it for me, and may also be for you.

good luck;

Traction Fan:smilie_daumenpos:


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## matisw (Jan 27, 2019)

it is a little confusing, but from what I gathered, a loco with sound is about $200 and the 9 passenger car set is about $175

Was thinking about one loco with sound ($200) and one dcc without (about $100) and then the 9 car set $475!!!! we'll see.


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## matisw (Jan 27, 2019)

withdrawn


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