Curve radius for passenger cars

[ATLANTIC CENTRAL]

Passenger cars, daiphragms and curves - here is what I do.

ALL my passenger cars are equiped with American Limited working diaphragms and the couplers are body mounted long shank Kadee regular head couplers - #36.

The couplers are positioned so that the diaphrams touch but do not compress under tension. the diaphragms stay touching under all operating conditions.

I have 60', 70, and 85' cars equiped in this way. They will run on curves down to 30" radius with no problem, they back up just fine, even in long trains through curves and turnouts and will go through an Atlas #4 customline crossover.

For me touching and working diaphragms are a necessity. Part of what maked all this work is the long shank couplers. Even though it is a small difference, moving the pivot point of the coupler back farther on the car results in less shrinkage of the gap between the cars as the curve gets sharper. This leaves room for the diaphragm and stops them from binding.

When backing the design of the American Limited diaphragm actually helps "push" the car, limiting how close together they can become. this prevents the long shank couplers from going "sideways" and binding.

I worked all this out more than a decade ago - it works great. BUT, I stil choose not to run long ars on tight curves - it looks toy like. If I wanted toy like I would have bought Lionel.

Sheldon

[Aralai]

Train Modeler

Longer couplers also don't help when you reverse.

Richard

Actually in my case they did, since it stopped the diaphragms from binding against each other.

[Train Modeler]

[quote user="Aralai"]

Train Modeler:

Diaphrams make a big difference on success and failure of a particular radius.   Particularly when backing longer passenger consists around a curve.    Some diaphrams are a lot easier to work with than others.    And the more protypical ones that come close to touching can be an issue on anything under say 36" when you back up or have super elevation.    After years of running long cars in long psgr  trains I have found 36" to be my personal minimum goal  for psgr routes.     

 

Good point. I had that problem. I ended up putting longer couplers on the coaches to separate them more which is not the best solution as the gap is not prototypical. Larger radius curves would look much better.

Longer couplers also don't help when you reverse.

Richard

[Aralai]

Train Modeler

There are at least a few additional items two consider

Diaphrams make a big difference on success and failure of a particular radius.   Particularly when backing longer passenger consists around a curve.    Some diaphrams are a lot easier to work with than others.    And the more protypical ones that come close to touching can be an issue on anything under say 36" when you back up or have super elevation.    After years of running long cars in long psgr  trains I have found 36" to be my personal minimum goal  for psgr routes.     

Good point. I had that problem. I ended up putting longer couplers on the coaches to separate them more which is not the best solution as the gap is not prototypical. Larger radius curves would look much better.

[Train Modeler]

There are at least a few additional items two consider

1.Super elevation will cause the top of the cars to come closer together.   So if you super elevate, consider an even larger radius.   This is also something to consider when setting up a second track and its' track center line. 

2. Diaphrams make a big difference on success and failure of a particular radius.   Particularly when backing longer passenger consists around a curve.    Some diaphrams are a lot easier to work with than others.    And the more protypical ones that come close to touching can be an issue on anything under say 36" when you back up or have super elevation.    After years of running long cars in long psgr  trains I have found 36" to be my personal minimum goal  for psgr routes.     

3. Making sure the cars are properly weighted can make it a lot easier.   A lot of the older psgr cars were under weight. 

Richard

[Aralai]

Curve radius is only one consideration for long passenger cars. Don't overlook 'S' curves - where a curve in one direction changes to a curve in the opposite direction. Long cars that have body-mounted couplers may reach a point on the curve where the couplers bind and derail the cars. I have found that passenger cars are especially susceptible to this - some of them have trucks that are set back farther from the front and rear of the car that freight trucks tend to be - making the problem worse as the swing out in each direction is amplified. Putting even a small section of straight track in between opposing curves helps.

[Paulus Jas]

well motley

add 4" to 6" on each side would mean a  2 x (30 + 5) = 70" wide table.

Add walk-around aisles (2 x 30") and the room space you'll need is about 130" ; or almost 11 feet in total.  Building a donut in that space would be a much better option.

Back to the original question, in the past ratio's were used.  A 1:5 ratio means the mainline radius is 5 times the length of the longest piece of equipment on your layout. This 1:5 ratio an-ables hands free coupling and uncoupling.

1:4  for very good looking

1:2.5  to 1:3 the compromise most of us have to deal with

1:2 is the lowest you can get, but it might limit train length, especially when pushing.

Which means that full body coaches need a 30" to 36" radius, and the appropriate #6 switches as well. Even #8's in S-curve situations like crossovers. 

Paul

 

[wabash2800]

You know, if part of a given curve is hidden, that part of the curve radius can be sharper to save space for the cosmetic curve. This is a trick that I have done in layout planning. On the prototype this can be a problem but not usually on our models as long as it is not overdone. I wouldn't attach a 22" radius curve to a 48" raduis curve but have attached my 42" cosmetic to a 30" functional for example. This works especially well if the there is shorter section of your costmetic and the longer section of sharper functional hidden. I am not talking spiral easements, I do that too.

[wabash2800]

Duplicate

[steinjr]

woodman

How much space will I need to accommodate a 30" radius on my layout.

 Depends on whether you need a turn back curve (i.e. a 180 degree curve at the end of a table) - in which case you need an about 62" wide table, or about 9 feet across the table, to allow for 2 feet aisles on both sides.

 If you are building a doughnut shaped layout you can do fairly wide curves on fairly narrow shelves or benches - since the center point of the circle the curve is part of can be outside the layout, in the aisle/operator pit.

 Quick illustration I have from an old discussion a way back:

 

 It is not a given that you can do a doughnut shaped layout, an around-the-walls type layout or anything like that. But if you can, the ability to have large radius curves on modest depth shelves is one of the great selling points of doughnut shaped layouts.

 

Smile,
Stein

 

 

[tgindy]

Overhang Test:  Place your passenger car on a 24" radius track (or radius drawn on paper) and observe (looking down) how much of the car "overhangs" on the inner part of the radius.  Also, how much of the track do you see on the outer side of the passenger car?

Repeat the test for a 30" radius and/or larger.  Which "passenger overhang" appeals most to you by appearance and performance?

[Motley]

Well let's see, 30" x 2 = 60"

And add about another 4-6" on each side for a loop. So roughly 66" wide benchwork for a 30" radius loop.

[woodman]

How much space will I need to accommodate a 30" radius on my layout.

[wabash2800]

I agree with Sheldon and Jim. 28-30" R, functional for HO.  And like Sheldon wrote. a miminum of 42" R for appearance on the larger cars if you want to couple them close like the prototype and look OK. My minimum on my layout for cosmetic is 42"R with easements but even then the longer passenger car bodes in the 80 some foot range  arc out a little on the curve. Having said that, I don't have a problem with 28-30" R on hidden track or helixes, as the cars will operate fine but not be seen, thus saving valuable space for cosmetic 42"+ curves out on the seen part of the layout. Well known modeler Bill Darnaby figured out that 42" R was the minimum to make a medium to large steam loco look good without the tender arcing into the cab or using an unrealistic drawbar distance btw the loco and tender.

Right now, I;m laying some double track with the outside main at 48"R and the inside at 46"R. Viewed from the outside the curve looks rather sharp. Model curves always look sharper when viewed from the outside rather than the inside.

[cuyama]

Curve radius rule of thumb from the Layout Design SIG.

[ATLANTIC CENTRAL]

Operationally, I agree with Jim, 28-30" is about the minimum for 85' cars.

From an appearance standpoint, I'm not even really happy with 36" radius for 85' cars.

42" or even 48" radius looks much more believable . I have 36" minimum and still choose to run mostly 72' "shorty" passenger cars for a better appearence.

I should mention that one of my "things" with passenger cars is close coupling and working/touching daiphragms. What is the point of all this scale accuracy and detail if we are then going to couple the cars miles apart to let them squeak around sharp curves? As our little scale passengers fall onto the tracks as try to move from car to car?

Sheldon

 

[wjstix]

A big issue is where the couplers are. On passenger cars like Walthers, with body mounted couplers, you'll want to stay around 28-30"R as Jim suggests. If you're using "talgo" trucks - trucks with the couplers attached, like Athearn, Con-Cor, AHM/Rivarossi etc. - you can get down to 22"R or even 18"R. In my experience, the type of coupler arrangement is a bigger factor than car length.

Of course, the larger your curves are, the better the cars will look....

[jrbernier]

  If you are talking HO - and 'full length' passenger cars - 28"-30" radius should be considered your minimum.  I know that Walther suggests 24" radius on the boxes, but for reliable operation you need to get up to about 30" radius.  Our club has 30/33" radius curves on the helix and that is the tight spot for trains.  I have a friend that tried to run Walthers HW Pullman's around 22" radius, but they bind up.

Jim

[woodman]

I will be running some passenger cars on my layout. What is the desired radius to use on the curves. What is the minimum I could use without having any issues. The cars will be Amtrack types and some older Penn RR cars.