Minimum Radius for HO

Model Railroader General Discussion (Model Railroader)
21

The original post asked minumum radius required, but that answer varies greatly.

6 Axle GEVO’s & SD70ACe’s can run on 22" curves, but do they look good? That is up to you. Similar sized diesels can do these same curves. Me - I like to run trains, and I have a few 6 axle units that will be run on my 24" mainline curves. I do know that some 6 axles can operate on as tight as 18" curves, but not all. (And only if they are not coupled directly to larger-sized cars.)

Bachmann’s 2-8-4 can handle as tight as 18" as well, but is better on larger 22" (or even bigger) curves. (Who doesn’t like 765?)

But bigger is always better, with the caveat that you must be able to fit bigger for it to be better. Sometimes space is tight, so we build what we can, where we can.

So, what radius is a very hard question to answer, as there are too many variables to consider for a blanket answer, unless that answer is “It depends.”

(But I’ve seen some really big equipment run on really tight curves in a pinch. One show I attended had a “show-stopper” on a 22" radii curve layout with zero derailments - a Bachmann Schnabel car! Everyone simply stopped to watch that thing, and everyone I saw was impressed!)

Last question about point to point with 42", or dogbone with 32" - You answered it yourself when you called the 42" minimum radii mainline “boring”. Build the dogbone with 32" curves, and enjoy it.

Will my trains “look good” on my 24" radii curves? My definition of “look good” on a model railroad is that they run smoothly, and that the operator finds enjoyment in it. So they will look perfect to me. [:)]

Your answer may be different, but when it comes to model trains, the only important answer about your layout comes from you. It’s your layout, build it where you can fit it, at the size you can fit, how you will enjoy it. If others prefer s

22

I’ll point to 2 philosophies to help you choose. John Armstrong (in a '50s MR article) separated model railroaders into 3 groups, based on operational preferences - dispatcher, spectator, engineer.

The dispatcher perfers the dispatcher role, keeping multiple trains (often each with their own engineer) running according to schedule and mission. Designing a good dispatcher layout takes considerable planning, and effort in executionl. In reality, there are very few dispatcher model layouts built in the US.

The engineer prefers to take his train over the line, doing what it is supposed to do (usually a way freight doing switching). The engineer serves as train crew, couping/uncoupling as needed for switching. Walkaround DCC is a very good fit for the engineer, a central console is not. An engineer layout works very well for a solo operator - one train at a time. Having more than one engineer simultaneously requires some thought during the design stage. Scenery is nice, but usually second in priority to opportunities for switching.

The spectator layout is designed for the model railroader who likes to watch his train roll through a scene(s). Scenery is usually crucial to the success of a spectator layout. Your starter train set is a spectator layout at its very basic.

Because of train sets and the continuous run, most model railroaders start off as spectators. Some-to-most eventually get bored with nothing but spectating. Some will get bored with spectat

23

That was from an article published by he who cannot be mentioned here. It’s somewhat more oriented to what looks decent on curves as well as reliable operation. My layout is a bit under that standard for example with minimum radius of 32", but only two curves that tight and one of them is the inner curve with a larger outter 34 1/2 radius.

24

Just from a functionality point of view, most HO equipment today will take a 22"R curve, but a few things like Walthers passenger cars or BLI’s 2-10-4 say they need a 24"R. In reality, some long cars may need some adjustments to the underbody to make 24"R curves however.

25

Joe didn’t do the original research, he published the results and added his take. My memory escapes me to be sure, but I “think” the original work was performed by the LDSIG within the NMRA. My tiny contribution was to examine how toy trains were able to circumvent the rules of thumb, and reliably use much smaller than the rule of thumb radii.

Reality is that using NMRA standards with quality track and rolling stock, a 2.5X will usually work out functionally - if appearance is left out of the equation.

Fred W

26

The shape of my last layout was a dogbone with the double tracked area running along the long wall. I operated it as point to point but wanted continuous running.

Operationally, I used the two turn back loops for industrial spurs, one being a load balloon track for a cement plant and the other a curved spur for corn syrup transload. They were scenicked in such a way as to have them look like they ended after the curve (short of connecting to the back straight). Operationally, the loco shoved cars onto the curved “spurs” and backed them off the same direction.

The second main line along the wall served no operational function in the pt to pt mode. It merely represented a Class I mainline that my shortline’s trackage ran parallel to. The interchange was nearby.

The turnback loops had a radius of 22 inches. That told me that I wanted short cars on those loops during ops, and that’s why I settled on shorty cement covered hoppers and corn syrup tank cars…typically 40 foot cars negotiating a sharp spur slowly…not unprototypical. The longer cars typically ran over the rest of the layout…gentler curves.

During continuous running, it was merely a display situation and having the longer cars looking a bit out

27

I hadn’t heard that standard before but it seems like a reasonable one based on my experiences. Some brands of full length passenger cars operate more reliably than others so that has to be factored in as well. Just one correction. An 80 foot passenger car is only 11", not 12". 80 feet is 960 inches. Divide by 87.1 gets you almost exactly 11". Now an 85 foot passenger car is almost 12". An 80 foot passenger car would therefore call for 33" radius. That’s very close to what I consider to be the minimum which is 32".

I designed my layout to have a 36" minimum curve on the mainline. On one curve I used a Walthers/Shinora #8 curved turnout which was advertised as having 36"/32" radius curves. I thought the 32" would be able to handle my full length cars. It was only after years of poor performance I learned that the inside curve was much tighter than 32" radius. Using my Ribbonrail gauges, I determined the inside curve was about 28" which explains why I had so many problems. I’ve since replaced it with a Peco #7 turnout which actually has broader curves than the W/S #8 and operation has improved tremendously.

28

I have used that 3x standard in the past, and it is reliable. I have Walthers and Rapido 85’ passenger cars as well as IHC 80’ passenger cars, and John’s calculations are correct.

I went down to my layout to measure these cars. The IHC 80’ cars are just over 11", and the Walthers/Rapido 85’ cars are just under 11.75". If you carry the calculations out four decimal points, you get 11.0218" and 11.7107", respectively.

As John indicates, they run well on 32" radius curves and, in my opinion, they look best running on 36" radius curves, or broader.

Rich

29

My minimum is 32" radius, but most of my curves are a bit larger. If anyone has a link to the topic on making Walthers passenger cars work better on curves, please past it in here.

30

If you follow the suggestion that I am about to make, you make hear some weeping and gnashing of teeth, but here goes nothing. There are lots of threads that touch on the topic of making Walthers passenger cars work better on curves. My suggestion is to start a new thread that will hopefully focus on this issue.

Rich

31

Nah, I’m not that far gone. But someone mentioned a topic earlier. If a link is posted, great. If not, I’ll forget about it until some time in the future.

32

[quote user=“richhotrain”]

John-NYBW

fwright

Curve radius is most closely related to the length of rolling stock you are going to use. A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation. Under this standard, min radius for a 40ft model car in HO (6" long) is 18". Full length (80ft) passenger cars (12" actual) need 36" radius curves. At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact. Coupling/uncoupling on 3X is normally not possible.

I hadn’t heard that standard before but it seems like a reasonable one based on my experiences. Some brands of full length passenger cars operate more reliably than others so that has to be factored in as well. Just one correction. An 80 foot passenger car is only 11", not 12". 80 feet is 960 inches. Divide by 87.1 gets you almost exactly 11". Now an 85 foot passenger car is almost 12". An 80 foot passenger car would therefore call for 33" radius. That’s very close to what I consider to be the minimum which is 32".

I have used that 3x standard in the past, and it is reliable. I have Walthers and Rapido 85’ passenger cars as well as IHC 80’ passenger cars, and John’s calculations are correct.

I went down to my layout to measure these cars. The IHC 80’ cars are just over 11", and the Walthers/Rapido 85’ cars are just under 11.75". If you carry the calculations out four decimal points, you get 11.0218" and 11.

33

[quote user=“IRONROOSTER”]

richhotrain

John-NYBW

fwright

Curve radius is most closely related to the length of rolling stock you are going to use. A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation. Under this standard, min radius for a 40ft model car in HO (6" long) is 18". Full length (80ft) passenger cars (12" actual) need 36" radius curves. At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact. Coupling/uncoupling on 3X is normally not possible.

I hadn’t heard that standard before but it seems like a reasonable one based on my experiences. Some brands of full length passenger cars operate more reliably than others so that has to be factored in as well. Just one correction. An 80 foot passenger car is only 11", not 12". 80 feet is 960 inches. Divide by 87.1 gets you almost exactly 11". Now an 85 foot passenger car is almost 12". An 80 foot passenger car would therefore call for 33" radius. That’s very close to what I consider to be the minimum which is 32".

I have used that 3x standard in the past, and it is reliable. I have Walthers and Rapido 85’ passenger cars as well as IHC 80’ passenger cars, and John’s calculations are correct.

I went down to my layout to measure these cars. The IHC 80’ cars are just over 11", and the Walthers/Rapido 85’ cars are just under 11.75". If you carry the calculations out four decimal points, you g

34

Hey guys, the LDSIG developed a “rule of thumb”, not a standard or a requirement. The radius rule of thumb allowed a quick look at a layout design with the anticipated equipment and givens/druthers to see if all was compatible. Haggling over whether or not couplers are included in order to “meet the requirement” is a fool’s errand, even though the LDSIG rule did officially measure over the couplers.

I use a test oval of 15" and 18" radius for my HO/HOn3 equipment to check compatibility and tracking issues. My modules comply with modular radius standards (much larger min radius), but my home layouts can have curves that small. Having the test oval helps prevent me from buying equipment representing too modern a prototype, and regretting the purchase later.

With my curves, I need to run Overton style passenger cars, and not even try to fit 60ft passenger cars, even though there were plenty of 60ft prototypes in that era. By having no long passenger cars to compare to, the shorter cars don’t look bad or out of place.

Fred W

…modeling foggy c

35

Good point, Fred. I was repeating the terminology from earliest posts. Usually, I refer to it as the 3x rule.

By the way, you have my quotes and Iron Rooster’s quotes mixed up.

Rich

36

[quote user=“IRONROOSTER”]

richhotrain

John-NYBW

fwright

Curve radius is most closely related to the length of rolling stock you are going to use. A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation. Under this standard, min radius for a 40ft model car in HO (6" long) is 18". Full length (80ft) passenger cars (12" actual) need 36" radius curves. At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact. Coupling/uncoupling on 3X is normally not possible.

I hadn’t heard that standard before but it seems like a reasonable one based on my experiences. Some brands of full length passenger cars operate more reliably than others so that has to be factored in as well. Just one correction. An 80 foot passenger car is only 11", not 12". 80 feet is 960 inches. Divide by 87.1 gets you almost exactly 11". Now an 85 foot passenger car is almost 12". An 80 foot passenger car would therefore call for 33" radius. That’s very close to what I consider to be the minimum which is 32".

I have used that 3x standard in the past, and it is reliable. I have Walthers and Rapido 85’ passenger cars as well as IHC 80’ passenger cars, and John’s calculations are correct.

I went down to my layout to measure these cars. The IHC 80’ cars are just over 11&q

37

Yes, in my experience, the stiffness of the Walthers diaphragms do contribute to poor performance out of the box. With each new car, I work the diaphragms back and forth several times to loosen them up a bit.

Rich

38

[quote user=“John-NYBW”]

IRONROOSTER

richhotrain

John-NYBW

fwright

Curve radius is most closely related to the length of rolling stock you are going to use. A rule of thumb was developed a while back that said you needed a minimum radius of 3x the length (in inches) of your longest car for RELIABLE operation. Under this standard, min radius for a 40ft model car in HO (6" long) is 18". Full length (80ft) passenger cars (12" actual) need 36" radius curves. At 3X body-mounted couplers will stay mated, and underbody detail can usually stay intact. Coupling/uncoupling on 3X is normally not possible.

I hadn’t heard that standard before but it seems like a reasonable one based on my experiences. Some brands of full length passenger cars operate more reliably than others so that has to be factored in as well. Just one correction. An 80 foot passenger car is only 11", not 12". 80 feet is 960 inches. Divide by 87.1 gets you almost exactly 11". Now an 85 foot passenger car is almost 12". An 80 foot passenger car would therefore call for 33" radius. That’s very close to what I consider to be the minimum which is 32".

I have used that 3x standard in the past, and it is reliable. I have Walthers and Rapido 85’ passenger cars as well as IHC 80’ passenger cars

39

Minimum radius tends to be dictated by the realities of the space available.

My minimum mainline radius will be 22 inches on hidden track, and 36" visible. My switching area will drop to 18 inches minimum radius.

It is important that all your equipment will handle the minimum OK. I have an obstacle course that I set up with Kato Unitrack and make sure EVERY piece of equipment that will operate on the layout will take a 22 inch S-Curve in both directions when coupled in between an odd sized freight car and a locomotive.

-Photograph by Kevin Parson

All locomotives must do it coupled to a 50 foot boxcar.

Anything that will run on the industrial section must do a similar test on an 18 inch sectional S-Curve test track.

-Kevin

40

Kevin I get what you’re doing and why you’re doing it, but it is no substitute for actually laying track on the layout and seeing the results.

Rich