How much weight?

Joe Brugger's picture
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George Booth's question about weighting rolling stock raises an issue I've been thinking about lately:  What is the right program for weighting freight cars? 

Do you take a different approach for a large, hilly club-size mega-layout than you would for a round-the-walls switching outfit?  Does it make a difference if trains will be long or short? What do you do about running empty flats or stack cars? 

In the past, NMRA standards (at http://www.nmra.org/beginner/weight.html) have seemed pretty reasonable, but my current club has chosen a heavier standard developed by the La Mesa club in Sandy Eggo (look under Model Railroad Operations at http://www.opsig.org/reso/).

Do free-rolling trucks and metal wheels reduce the need to weight cars? Is car length, or the number of axles, the best way to set weights? Or, are they fine the way they come out of the box?  What are the advantages?




Eric H.'s picture

Less Weight

Joe,

Take into consideration the La Mesa club has a layout that goes beyond what most of us could do on our own, size-wise, operationally, scenically, and about everything, I just responded to George Booth's post regarding the NMRA Recommended Practice for weight, RP-20.1. If using many of the more recently designed and manufactured trucks, I don't feel the full weight suggested by the NMRA RP is appropriate. I calculate the weight as per the NMRA RP but aim for 75% of that total, which makes it easier to add the proper weight to hopper cars.

Eric

Eric Hansmann
El Paso, TX

Follow along with my railroad modeling:
http://designbuildop.hansmanns.org/

watch those metal wheels

roll downhill!  And don't add too much inetia (weight)  to them! 

I'm with Eric... examine what YOUR layout needs, and trim the weight from NMRA specs.

My layout has 2-  2-1/2pct grades... so weight is revealed when engines slow down on the upgrades.   But I look first to rolling properties... staying On the rails.   I'd do things a bit differently for a flat layout.  Nothing like a 100 car drag!

 

As I opened... metal wheels on modern trucks change rolling charateristics... so keep that in mind, too.

- regards

Peter

Joe Brugger's picture

Peter, Eric, do you have a

Peter, Eric, do you have a specific formula you use, like the NMRA's X ounces per car plus x ounces for 10' of car length? 

It does seem helpful to keep car weights consistent. My line only has about a 1.2% ruling grade planned, but the club has a lot of 2% and maybe some 2.5% . . .  not that cars migrate back and forth.

Bob Langer's picture

May I suggest a calculator

May I suggest a calculator? There is a car weight calculator in Easy Model Railroad Inventory. On the main menu click File > Calculators.

They can also be accessed from the Utility open on the Outlook style menu on the left.

Eric H.'s picture

Simple formula: 75% of the recommended practice

I start with the NMRA Recommended Practice 20.1 that covers weight for rolling stock.

http://www.nmra.org/standards/sandrp/rp-20_1.html

While the document is noted as Revised Jan. 1990, it follows pretty closely to what was originally created back in the late 1950s and early 1960s. At that time the rolling characteristics of freight and passenger car trucks left much to be desired. Weight was considered an important factor for tracking and rolling.

Today's materials and supplies are much better than those of fifty years ago. Newer trucks by Accurail, Atlas, Branchline, Intermountain, Red Caboose, Tahoe, Walthers, and others are made of a much more 'slippery plastic, and are created with finer tolerances than the products that were in use with this NMRA Recommended Practice was implemented. If a piece of rolling stock needs weight, I will calculate the weight as per the NMRA RP but aim for 75% of that total. BTW, aiming for 75% of the NMRA RP makes it a lot easier to add appropriate weight to hopper cars.

So let's use an HO scale 40-foot box car as an example. It is just over six inches in length. Using the NMRA Recommended Practice we start with an initial one ounce weight and add a half ounce for each inch of car body length. Again, the 40-foot HO scale box car is about six inches in length. Multiply six inches and half an ounce and you get three ounces. Then add the one ounce of weight and you would have the weight following the NMRA Recommended Practice. I take one more step and take 75% of that total weight, done by multiplying the total by 0.75.

For this HO scale 40-foot box car, 4.0 ounces multiplied by 0.75 equals 3.0 ounces of weight. Most HO scale box cars weigh at least three ounces so I do not add or subtract any weight. If the 40-foot box car model is lighter than three ounces, then I'll add some weight to meet or slightly exceed the three ounce target.

I target 75% of the NMRA Recommended Practice for HO scale car weights for each model in the freight car fleet. Som emay weigh a little more than that but none exceed the NMRA RP.

Eric

Eric Hansmann
El Paso, TX

Follow along with my railroad modeling:
http://designbuildop.hansmanns.org/

   Joe.  The old NMRA

   Joe.

 The old NMRA recommendation was based on track work that was not nearly as good as even our manufactured track of today. With tapered wheels and added weight was an acceptable way for keeping cars on bad track. The club I am in had an NMRA standard for weight in rolling stock but had no standard for wheels. Last summer I did a demonstration on rolling stock that has since dropped the weight restriction and added metal wheels to all rolling stock used on the layout. I placed an empty flat car with just the sheet metal weight that came with the car equipped it with free rolling metal wheels and just as important free moving couplers. The car was placed behind the locomotives and 64 more cars were placed after it. Even with pushers on the 2.5 percent grade there were no derailments. The train moved on every district and yard. I even backed the train around the sharpest bends and up the grades at speed with no derailments.  Weakening the centering spring in the couplers allows the car to be coupled at switching speeds with very little movement.

 It is proven that weight is a detriment to railroad operations. Smooth track, free rolling metal wheels, Three point suspension, and free moving couplers is the way to go for smooth and enjoyable operations. Adding weight that is unnecessary is an excuse for bad track, and poor rolling stock maintenance.

     Pete

      Pete

How much weight

I'm a bit late replying to this thread but I would like to confirm that the NMRA RP is heavier than necessary and creates tractive effort problems on many layouts, especially if you want to run full length trains up and down scale grades with steam locomotives. It is also next to impossible to build many flat wagons and skelton type container wagons to the NMRA RP recommended mass.  Using a standard heavier than the NMRA RP is going to result in a shorter life for bearings. The only advantage of extra heavy cars is improved coupler operation when shunting single cars. However the new scale Kadee couplers now require less coupling force, so the argument for heavy wagons is now negated. Theoretical analysis shows increasing weight or decreasing weight does not change the maximum train length that can be pulled or pushed, assuming unlimited locomotive traction and using a simple mass to length ratio. This is consistent with my personal observations. The Europeans have for years used a much lighter weight standard with a simple mass to length formula of 0.4g/mm minimum for H0. I now use this for passenger cars. For freight cars I used to use 0.57g/mm (about 1/2oz per inch).  Now I have gone slightly lighter to be consistent with the Australian Model Railway Association standard (at   http://www.amra.asn.au/standards.htm ). It can be theoretically shown for tension a linear formula like these produces the best result if cars end up in different positions in the train. For compression if all the cars are to the same length to weight ratio, then the maximum train length is related to the minimum car length. The longer the car length the longer the train. Looking at it a different way, the maximum number of cars that can be pushed is a constant number of same length cars. From experimentation, using free rolling modern models, the maximum length that can be pushed on flat track is in excess of 80 wagons of the same length. In tension, the maximum length train is in excess of 130 wagons of the same length to weight ratio. These tests were using H0 models with body mounted Kadee couplers.

 

Terry Flynn

 
http://angelfire.com/clone/rail/index.html

HO wagon weight and locomotive tractive effort estimates

DC control circuit diagrams

HO scale track and wheel standards

Any scale track standard and wheel spread sheet

AMRA standards http://www.amra.asn.au/standards.htm

 


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