Hello Everyone,
Is there any correlation between lenght of rolling stock or locomotive and minimum track radius in HO scale? For example, a 40’ hopper car would run well on a minimum 16" track curve or a 72’ locomotive would run well on a minimum 22" track curve.
Prepare yourself for a lot of different opinions on this one.
Here is my take.
Regarding minimum radius, 16" is below minimum standards for HO scale. 18" is widely considered to be the bare minimum. 22" to 24" radius works well for short equipment. 26" to 28" radius is better. 30" to 32" is best for a minimum radius. If you want maximum flexibility and the space to pull it off, 34" to 40" radius would be highly desirable.
As far as equipment goes, if you are running steam, every pair of driver wheels requires a broader radius. For example, an 0-4-0 will negotiate 18" radius, but a 4-6-2 really needs 22" to 24" radius to perform well. A 4-8-4 really needs 26" to 28" radius to perform well. A 2-10-2 or 2-10-4 really needs 30" to 32" radius to perform well.
As for diesels, 4-wheel (2 axle) trucks perform well on 18" radius and broader, but a 6-wheel (3 axle) truck diesel really needs 30" radius and broader to perform well.
Just my [2c] based upon my own personal experience.
Rich
Thanks for the feeback Rich. I’m working on a layout design for steel mill operations that will connect to a larger layout. The steel mill will use mostly smaller rolling stock and probably switcher locomotives. With that thought in mind, I was looking to see how low of a radius I could go.
The first club I belonged to was a round robin type where we would visit each other’s house for layout construction and operations. Half the club members were trolley addicts and they would use 10" radius curves and we found out a small switcher and 40’ cars would go around those curves. Since you are doing a steel mill with those small cars that would be approriate, you can put down some small radius track and check out your equipment and find a true minimum radius for your operations.
Rick Jesionowski
There is a GENERAL forumula. The radius is generally recommended to be 3x the length of the rolling stock. Let’s take a 85’ passenger car. 85/87.1 (scale) = .97 or 11.72". Take that and multiply it by ~3.
That’s for smooth reliable operation that looks appropriate. And most will tell you 32" is about right for passenger service. But Bachmann will make passenger cars that run down to 18" thanks to their innovate coupler design. But the curve between cars, and track overhang isn’t prototypical looking. There’s large gaps.
Also when running long cars, you have to increase distance around parrallel curved tracks. Most parallel tracks are 2" apart (HO scale). Around curves you’ll have to increase this to almost 2.5" for passenger trains around tight curves. This is to keep “clothes lining” rolling stock from bumping into each other around curved tracks.
My layout has mostly 18 inch curves in HO. I run Transition Era equipment, mostly short diesels and 40 or 50 foot freight cars, plus some short passenger cars.
I have to be careful about what I buy, but I have a 2-6-2 Hudson and a 2-8-2 Mikado steam engines that negotiate all my curves very well. I think both of these have some unflanged, or “blind,” driver wheels.
Most of my freight cars have body-mounted couplers. My passenger cars have either old truck-mounted couplers or body-mounted swing couplers that allow tighter curves.
As you leave the Transition Era, though, everything started getting longer. I have one diesel that won’t take my curves well, even with nothing attached to it.
Going back in time won’t help, either, particularly if you are running older large steam engines or passenger cars from those thrilling days of yesteryear when intercity travel by train was a luxury, not the ordeal it’s become now.
Quite a bit of correlation between length and the minimum radius a car or locomotive can be run on. This is true for the prototype too by the way. I think it is safe to say that a great many of our model trains in HO are engineered to fit on a certain minimum radius curve, be it 18" or 22" or whatever, for which prefab sectional track is available, and that what that means is that there are compromises with prototype fidelity to make it so. Same for N and its sectional track 9" and 11" curves.
Other factors relate to things like, are the couplers mounted to the car or locomotive body (as are prototype couplers) or are they mounted to the trucks and can swing further out? This is particularly noted with very long freight cars and passenger cars. The rigid wheelbase is another controlling factor, steam locomotives of course but also things like the EMD DD40 wheelbase or certain electric locomotives.
This is why so many model articulated locomotives follow the lead that Rivarossi did which is to have BOTH sets of “engines” under the boiler be able to pivot, versus the prototype where the rear engine was rigidly attached to the boiler and only the front engine could pivot. Rivarossi also introduced much more side play into the drivers than the prototype did. A true accurate scale model of, say, the N&W Y6b 2-8-8-2 could never handle th
What size switcher are you thinking about?
Rich
The walthers hot ladle torpedo cars are “very touchy” due to the design. I would not go lower than 18" on those btw. Ingot cars can go down to 15" with a plymouth switcher.
Something like an EMD SW1001, moving coke cars, ore cars, coal cars, ingot cars or hot ladle torpedo cars for steel mill operations. Any cars going out of the mill area would go to a staging yard where larger locomotives would move them to other areas of the layout.
I’m with Don (Digital Griffin) on this one. 15" radius would be challenging, but you should be able to accomplish your goal with 18" radius, using an EMD SW1001.
Rich
Gidday Don, you’ve been given some very good advice but what I do in this circumstance is to lay some flex track in the tightest radius that I can / want, hook up power if required, and actually see if whatever I ‘m trialling at the time, works.
In this photo I was seeing how the mocked-up span bolster would run connected to a 50” car, it was the worst possible scenario, and from memory, 12” was a definite no-go, a 15” radius was a pinch!
Cheers, the Bear.[:)]
All model railroads use radius that is far too tight. The main impetus to use broader radius curves is how the moving trains look rather than what will work.
The best rule of thumb is to use the broadest radius that will fit.
Unless you have really a lot of space then the radius you get stuck with will be too tight so make it as broad as you can.
The 3x length of longest car is a useful rule of thumb and without knowing of that useful guide that’s what we ended up with pretty much. 24" is pretty tight from an operations perspective. Our tightest curve is 22" and we were forced to use that. Otherwise we tried for 24".
I built a small Christmas layout that used 15" radius curves. I ran a small 040 switcher with short passenger cars with no problem. Short ore cars should be fine with this.
I’ve been to a few steel plants and iron mills in my life. There was some tight turns and long gons going over those old rails. Trackwork was not too cared for. The plant switchers were broken down seventy ton jobs to rubber tired loaders with a coupler mounted on the back. Hoppers and ore cars rarely went near the plants and materials were conveyed in. Flats and gons and purpose built steel coil cars were the norm around the plants and rolling mills.
Pete.
I am not sure HO works that way. Train sets come with an oval of Snap Track with 18 inch curves. Every manufacturer in the industry does every thing they can to make their product stay on the 18 inch curves. There used to be, maybe still are, a lot of kid’s toys out there. Any piece of rolling stock that will work on the train set curves has a much bigger market than those that won’t. There are a lot more kids running trainsets than Master Model Railroaders running hand laid track. I would not count on any HO rolling stock working on less than 18 inches.
Car length is the determining factor. 18 inch curves work with four axle diesels, 40 and 50 foot cars, and medium size steam, 4-6-2 Pacifics and 2-8-2 Mikados. Passenger cars are tricky. Some, the Athearn passenger cars in particular, will run on 18 inch curves. Full length 80 foot passenger cars need at least 24 inch radius curves. Truck mounted couplers will get a long car around sharp curves better than body mount.
A compact area with short cars being shunted over sharp radius curves can be pretty cool.
Also consider the turnouts.
Another thread highlights the difference between turnouts, where the diverging track is curved througout the turnout…which would be really cool for you area in places…and turnouts that are straight through the frog and diverging route. These types of turnouts generally require a bit more space.
Depending upon which code of track you use, Atlas makes a snap switch in code 100 that has an 18 inch radius…I think, at least it used to be 18, and a code 83 product that has a 22 inch radius curve as the diverging route.
Peco also makes curved radius diverging paths in their code 100 line…small radius turnouts .
Atlas makes both 18" and 22" radius snapswitches in Code 83.
The question really isn’t so much “How tight is too tight” to operate, as things can be made to run on very tight radii if needed, but some “cosmetitc surgery” will be needed.
But when dealing with larger equipment, it does look funny on smaller radii.
Things like the Bowser C630/636, Atlas 8-40C/CW, even a Scaletrains GEVO will handle 18" radii, hauling coal, frac sand, oil/ethenol tanks, 60’ flat cars, grain hoppers, 60’ or shorter box cars, etc… But they look pretty funny doing it.
Conversely, 80’+ cars, like autoracks, will not handle that 18" radii without heavy modification.
So when dealing with tight radii when needed, things can be made to handle it, but the question of “will I like seeing it” is vital.
Did a lot of experimenting years ago as some people like to use longest radius possible. Found out 18" radius looks fine on 40’ cars both inside and outside radius curves and flat cars and other low profile cars can still look fine beng a bit bigger. 50’ cars run fine but look bad. Many engines can run fine and don’t seem to look bad larger but smaller look better and some that will work that are really large look very bad so make your own mind with engines, particually diesels as they generally have a profile that is not broken up.
