A surprisingly basic N Scale question about curve radii

[Ed Kapuscinski]

After my build of Seidelmann Run I've been revamping my future layout plan to take advantage of what I've learned.

One of the things I've been rethinking are some curves.

As much as I want to plan around 19"+ radii, there are some situations where a little bit of cheating and going lower can unlock some big benefits.

So, with that in mind... when it comes to 15" radius curves, do any of you experience performance issues with them?

I know they're far from ideal from an aesthetic perspective, but can I get away with them if I'm not worried about that?

For reference, my anticipated train length is about 10' and I'm expecting to be able to run 89' flats on trains.

What do you all think? Can I get away with them?

[Dave V]

15" should do whatever you need. I had 15" radius outside curves on the old Juniata Division and I didn't have any restrictions on long equipment including 89' TOFCs, passenger cars, M1 locomotives, or auto parts boxcars. You should be fine.

[Ed Kapuscinski]

Glad to hear it.

That's going to allow me to place about 12' of visible run between Cockeysville and Parkton.

Should be a nice and scenic ride for those commuters in their unheated 1920 vintage coaches...

[MK]

I don't think you will have any issues.  I've ran my Kato N700S Shinkansen on T-Trak standard corners with no performance issues.  The cars are just under 90' long on the prototype.  Mind you these are Kato equipment and they are designed to run on 9-3/4.   

[C855B]

Representing an opposing view...

Even with transitions, I fudged a planned 24" curve into roughly 18". I had problems with long car-short car couplings wanting to lift, especially long loco-short cars (six-axle next to an ore jenny). I had to re-lay about 5' of track to get a 24"R. Also for other spots on the RR the ore train had to have SD-SD-GP on the point for the shorter loco. Body-mounted couplers, obviously.

[John]

My last layout was 20-24 curves (mostly) .. the current build is 18' mostly, and some 15" .. it should be fine

[Dave V]

I can get a T1 and P70s around an 11" radius curve (even though it looks like a shopping mall choo-choo ride)...

[robert3985]

My minimum visible mainline radius is 24", with my absolute minimum radius being 18" for "hidden" trackage and yard/industrial/branchline trackage.

Since my era is 1947 thru 1956, I don't run a lot of really long freight cars, but being a mainline UP theme, I DO run long wheelbase locomotives, such as FEF's, TTT's, E units, Standard Turbines, and, of course Big Boys and Challengers (which, because they are articulated, I don't really consider to be "long" wheelbase).

Although I am in the process of body-mounting all of my couplers, I still have a lot of cars that have their truck-mounted couplers attached, so, my main interest is cosmetic, not operational, and I don't experience any problems on 18" radius trackage.

However, on some trackage, I've cheated some to gain a bit of scenery between rails and the edge of my layout's fascia by running my 24" minimum radius but inserting a small length of 18" radius trackage at the apex of the curve...with equivalent trackage radii for my adjacent larger-radius parallel trackage 1.5" away.

From a cosmetic standpoint, this 6" difference in radius isn't noticeable on long trains or operationally with my long-wheelbase engines running long passenger cars, but gains me quite a bit of scenery near the edges of my layout, or at least enough so that I'm not worried about knocking my cars off the layout with a stray elbow.

I also take advantage of tunnels that happen to be located on a curve and treat these areas as "hidden trackage" making the minimum radius 18" if the tunnels are long enough (all my tunnels are twin-bore), and also through deep cuts.

And, I attempt to use spiral easements leading to and from most curves originating and ending at sections of straight trackage, although this definitely is not a space-saving protocol.

I assume that short sections of smaller-than-minimum radius trackage inserted into minimum radius curves shouldn't cause much of a problem...to a certain point of course.

I always use my old Cadrail app to plan my trackage, then print the plan out at 100% so my trackwork is very precise, and making it easy to transfer spiral easements to my benchwork.

Cheerio!
Bob Gilmore

[thomasjmdavis]

My previous layout had 15" curves (with easements).  The only cars I had any issues with (that weren't related to a couple of trackwork problems that were eventually resolved) were Rapido, Walthers, and some kit-built 85' passenger cars with body mounted couplers.  Mostly due to my own stubborness about car spacing, and therefore diaphragms pinching when on curves.  Also the occasional issue with a body-mount to truck-mount coupler issue. 

My recommendation (and I am following my own advice as I begin a new layout) is to tack down some flex track in the curve radius you intend to use, and do a trial of anything you think might be a problem (long steam loco, passenger car, trailer-train flats, etc).  Sometimes, all you need is an extra 1/4 inches, sometimes 4 inches, sometimes trading one brand of cars for another.  Or, you get lucky, and find that everything works on the first try.

[ednadolski]

With no grades, 15" r. with a 10' train seems it should be fine with most rolling stock, unless perhaps you have an exceptionally long overhang (on the rail cars, that is).

Ed

[Point353]

So, with that in mind... when it comes to 15" radius curves, do any of you experience performance issues with them?

Spiral easements are your friend.

[randgust]

My 'big layout' (not Ttrak) has 15" visible main line curves.    The hidden track goes down to 11", which is what seemed logical then anyway.

My 'hill climb' up the Arizona Divide is 2.5% with a 90-degree 15" reverse curve, grade compensated, at the top.   That's where if anything is going to stall out, it's going to be right there, around that 15" curve.    Viewpoint is from inside, not outside, think like Horseshoe curve, so the optics are fine.  But operating is another issue.

And that is where it does separate out the pack.   I have multiple 30+-car trains with 3-4 units, and it's on the ragged edge on that hill and curve combination, it's when things happen:

1)  low flange wheels (like the ill-fated MT plastics) will climb the inner rail on the front end cars, had to remove them.   Pizza cutters do not, and the new ones do not.
2)  Atlas piggybacks with those short shank, body-mount couplers repeatedly stringlned and overturned - no other 85' car from any manufacturer everhas
3)  I had to modify and take center axle flanges off my Hallmark 4-8-4, it didn't like those 15" curves at all.
4)  Mixing body-mount and truck mount standard passenger cars does not go particularly well, but it's close.
5)  My 'original' Life-Like Berkshire with the drawbar at the back end would climb the outer curve rail on every 15" curve under load.   Moving the drawbar behind the rear axle fixed that.

My 'flat' 15" curves are also superelevated, and that makes a big visual difference.   Very little difficulty there and that has not caused issues.

So if you are going 15", you're probably OK, but adding in heavy trains and even a mild grade makes things more interesting than you may want.   That hilll and curve are also what made me into a tractive effort fanatic over time ranting against slick wheels and light locomotives as yanking a heavy train up and around starts testing physics, just like on the 'shoe.   I'm quite 'dug in' with six-axle Classic Katos for the heavy haul work.

[seusscaboose]

Ed
if you recall, in Op's at my place... i had a return loop under the staircase... it was 15 inch radius.... no worries running The Daylight or The Broadway Limited during the intense TT/TO sessions

always on time

never a derailment there

EP

[Ed Kapuscinski]

Aight, sounds like I'm good to proceed, with a tiny bit of caution.

[Dave V]

Yeah, FWIW, my 15" radius curves were zero grade and ever so slightly super-elevated (I think if I recall it was 0.010" under the outside rail).