What is the minimum practical radius you guys would recommend for N-scale that could accommodate all sizes of rolling stock with the least amount of derailing etc??
I plan on using a tighter radius in my staging area than on my layout… the staging will be its own deck and fully accessible.
Any suggestions would be great!
You’re going to get lots of different answers on this one. What looks good and what doesn’t derail…these are different number radii. My preference for looks would be 14" radius. For reliability I’d say 11". There may be some specific steamers that will not negotiate an 11" radius, but I don’t own one. Others might.
I made a decision to use 11" min radius for my layout (well actually there is one double track where the outside loop is 11" the inner one is 9.75"). I have some sections with wider radius.
Eleven inch R is enough. If enough works for you. It may not handle a Big Boy or Challenger, but I don’t have either. My olf MiniTrix Decapod was able to make the turn OK on an 11" radius Diesels are not a problem.
But if I ever build another layout, I would strive for a wider R, just for aesthetic reasons. Eleven allowed me the reach I wanted, but it does look silly when long cars overhang the track like they do on an 11" R. My RDC tracks fine, but looks silly. Option of course is to only run short box cars and diesels.
So - eleven is enough - but 16 or even more would be better.
I went with 11 3/4", short cars are ok but passnger or modern trailer trains or well cars do look silly and with mirco-train, it’s reliable enough. If I have space and a new layout, I would actually aim for 16-19".
The caveat of “all types” of equipment makes this a toughie. It makes the answer the largest your space will allow. For reliability, I would recommend using easements into the curves regardless of radius. On extremely large curves the easements are mostly for asthetics. For everything else they allow the rolling stock to gradually enter the curve. Easements will cost you somewhere between 1/4" and 1/2" of space, but will be worth the trade.
The Layout Design Special Interest Group (LDSIG) has a rule of thumb (http://ldsig.org/wiki/index.php/Curve_radius_rule-of-thumb). It states that minimum radius should be 3 times the length of your longest car or locomotive, measured coupler to coupler. For an 89ft car in N, this means 3 times about 6.5", or a minimum radius of 19.5 inches.
The rule of thumb is based on body-mounted couplers, and sufficient margin that too-sharp curves will not be the cause of your derailments. In N, I have never heard of anybody encountering string-lining that was not caused by truck or wheel problems when following the 3X rule of thumb. But since most rolling stock in N does have truck-mounted couplers, you can normally “cheat” down to 2x longest car length without problems (except stringlining with long trains on grades). This last point supports what other posters have said, that 13" will work reliably as a minimum radius.
The rule of thumb states a need to increase radius for good looks from reduced overhang, and to be able to couple reliably on curves. When you apply the beginning note regarding speed and Note 4 regarding truck-mounted couplers, you arrive at a minimum radius of 21.5" using NMRA RP 11 (see http://www.nmra.org/standards/rp-11.html). This is based on both appearance and recommended model construction practices.
Long cars and locomotives need big curves to look realistic and operate well. But as always, these are just my thoughts, you make your choices for your layout.
Fred W
Being somewhat new to n-scale coming from HO, I made the mistake of using 9.75" radii and for all the engines I had this was fine.
However I went to get another engine recently and found out that several engines require a min. of 19" radii.
What it comes down to is if your engines and couplers on said engines are attached to the wheel trucks, you shouldn’t have any trouble with 9.75" or greater. However if you want to make a more “compatible” layout where several engine types can run, I’d shoot for 19" at a min. Any engine where the coupler is attached to the frame and not the wheel truck, expect a lot of rolling stock de-railment if using < 19" radii
I regret not doing this as it does limit my engine selection. I’ve already begun a layout in my head using 19" for this reason alone.
I can’t speak with any authority or even much personal experience, but I’ll throw in my 2 cents after all the researching I did. I’ve made 13.75" and 15" my minimum radius on the double mainlines for my first layout.
The upper line I’ll dip down to 12.5" if I have to, but that’s the bare minimum, and it’s only single track, so I don’t have to worry about clearance between passing trains on two tracks.
I conducted some loose testing with my Bachman 4-8-4 Northern and ER Models Sharks on the Bachman easy track that uses 11.25" radius turns. I strung together 12 cars behind each engine and played with various grades on those tight-ish turns and they all worked well enough even at silly grades without stringlining or derailing. I think I got as bad as 4 or 5% grades, so my planned maximum of 3% should work as well.
Nineteen inches is pretty wide! What do you have that requires that? In general terms 18 is considered broad in N scale, and more than that is for cosmetic than operational reasons, at least that’s what I though I’d learned!
I don’t have anything that requires 19" that now, thanks to a good relationship with my LHS 
Any engine that has the coupler mounted to the chassis and not the wheel trucks require wide turns. All (to my knowledge) of the bachmann 6-6 diesals “require” 19". I suspect you could get away with less and maybe get it to work but I know 12" isn’t enough for those 6-6 engines.
Check out bachmann’s website, it states right there they “should have” 19". After looking through my LHS I noted several rapido and knuckle n-scale engines where the couplers are mounted to the chassis. The problem that I’ve experienced is that when you enter a turn of even 12" the first wheel set of the first rolling stock ALWAYS came off the track. I tried two different engines both had rapido’s, both had the same problem. Not saying “everyone” would have these troubles, and I’m not a “guru” of n-scale as I’m still new to the hobby.
If you stick to products that have couplers mounted to the trucks I doubt you’d have a problem, you move to a product where the coupler is mounted to the chassis, well I think you’ll see what I’m talking about.
To further qualify my posts, I’m talking about the 6-6 diesels from Bachmann, with rapido couplers, althought I don’t really see how a knuckle would change anything as it isn’t an issue of un-coupling but how the body of the engine pushes the first rolling stock off the track.
Thanks everybody. My staging area won’t be scenicked and the radii would reflect a fly-over loop to help restage… although I’m looking to avoid one if possible as they can cut your staging significantly.
My minimum radii on the modeled portion of the layout will be 20" with easements.
The bigger the radii - the nicer the look. Big sweeping curves are easily acheived in N scale as opposed to HO. A 20" radius is sweet. And don’t forget to superelevate 'em.
You would be safe with a minimum of 11" or 12". I run six axle diesels with autoracks and twin stacks on 12" radius without any problems. If you can afford the space a bigger radius will be better.
Cheers,