Car Weighting

[mmagliaro]

Otto, my theory about weighting all the cars the same is this:

I only run 33', 40' and 50' cars (not counting passenger cars, which we'll get to in a minute).
The actual difference in the lateral stresses on a curve caused by these differences in length (2.5", 3", 3.75")
in N Scale just doesn't seem like it would be much, especially if you have reasonable curves (mine at 18" and wider).

Thinking about a train of, say, 50 cars.  Let's say we had a 33 footer in front and weighted it less,
like the NMRA practice suggests and had all the 40-50' heavier ones behind and we tried to pull or push that
string through a curve. 

I think the lighter car is at risk of pushing off the curve more easily than the heavier
ones and it doesn't really matter how long it is.   
It seems to me that 50 equally weighted cars would have less chance of
the light ones being "sprung" off the curve. 

I have no scientific proof.  It's just a gut feeling.

Now, with longer stock, 60', 89', etc,  I can see how those might need more weight.   

Oh, and as for passenger cars... same logic.  Having them all the same weight, I think, would work best, even among
60', 72', and 80' in a string.

[pjm20]

Why run smaller consists?  Just add more units on the point, as the prototype does. I've never understood the aversion to adding motive power, whether on the point or in helper or pusher service. And it's easier in DCC with speed-matching and consisting.

My question sort goes on the lines if your prototype didn't use helpers. Say your prototype used only one or two engines to run a train of 50+ cars. I'm not sure if you could overweight cars in this case. I was merely speculating on why some people like to overweight and some don't, because if it led to a lot of the improvements I keep hearing about, wouldn't everyone overweight their cars?

[bbussey]

... I now use springs in caboose axles to put an extra drag on the tail end of freights ...

I also do this.  At least two springs – one on each truck, diagonally opposed.

[bbussey]

My question sort goes on the lines if your prototype didn't use helpers. Say your prototype used only one or two engines to run a train of 50+ cars. I'm not sure if you could overweight cars in this case. I was merely speculating on why some people like to overweight and some don't, because if it led to a lot of the improvements I keep hearing about, wouldn't everyone overweight their cars?

Two engines should be able to pull 50 cars.  And if that was the prototype, then the terrain must have been relatively level.  For roads that traversed mountains and valleys, such as in the northeast, more than two units were put on the point.

I never said that overweighing should be the new standard.  I find it to be an advantage.   Max believes he achieves the best results having all equipment the same weight and running with MTL trucks as the primary factor.  I believe center-of-gravity and body-mounted couplers are the primary factor over weight, even though I prefer cars with more weight if possible.  I definitely don't agree with the no-weights theory posited in recent months where one engine can pull 100 cars, as the operation of those cars bouncing and twitching over every minor track imperfection is problematic in my mind.  But people should weigh their cars based on what they prefer.  I don't think there's a "right" or "wrong" in this situation.

[shark_jj]

Here are two non scientific observations.  The ruling grade on the Grand Trunk Southern is 2.6% in the helix.  Normal train length is 30 cars.  Minimum radius is 18 inches.  If unweighted cars are at the front of the consist, I will see a derailment about 50% of the time.  If the unweighted cars are placed at the rear, no derailments.  I started weighting all cars the same by adding 1/4 Oz of weight over the wheelset.  Derailments disappeared.  Had the same experience on my previous Horseshoe Curve layout.  Trains with light cars at the front of the consist would suffer a derailment at the bottom of the curve.  With the added weight most of my cars end up weighing 1.1 or 1.2 ounces which seems to be sufficient regardless of car length.  This is slightly above nmra standard on 40 ft cars, pretty well dead on for 50 ft cars, and slightly light for larger cars.  It doesn't seem to matter as long as the added weight is right over the trucks.  Clearly with weighted cars pushing unweighted cars on a curve, downhill, there are forces at play which cause the car to ride up and off the track regardless of how good your track work is.

[VonRyan]

We also have members here who remove as much weight as possible (but they haven't chimed in yet).

Yes. If the weight is not structurally important to the car, I remove it.
All except cabin cars, which I prefer to have a tad bit of weight to stretch the train out.
Any derailment I've ever had since I started leightweighting cars have only been due to: low trip-pin, track issue, errant children hands.

[pjm20]

What's the reasoning behind underweighting cars? (not a criticism, just curious)

[peteski]

It doesn't seem to matter as long as the added weight is right over the trucks. 

Really?  The placement makes a difference?  I would think that is a car's floor which is flat and stiff (like floors are) and it is supported but center-pivot trucks located close to the outboard edges, then as long as the weights were anywhere between the pivots the car would behave the same way as a car with the weights right over the trucks.

For example a 1/2 oz. thin flat sheet of lead long enough to fit between the truck centers and as wide as the floor width would be the same as 2 much smaller (but thicker) 1/4 oz. lead weights placed over the trucks.

No?

I'm even thinking that since a flat weight would be more beneficial than small but thicker weights, since its center of gravity would be slightly lower.

[VonRyan]

What's the reasoning behind underweighting cars? (not a criticism, just curious)

It primarily allows for locomotives to pull prototype-length trains, and it reduces stress on the mechanism.
I want my locomotives to be able to pull a prototype-length train up a grade on a curve.
I'm also slowly changing things over to metal wheels so that the center of gravity is as low as possible.

[pjm20]

So, how many cars are we talking about here? And what about the grade you mention? Do you have any problems with string lining?

[Cajonpassfan]

Otto, my theory about weighting all the cars the same is this:

I only run 33', 40' and 50' cars (not counting passenger cars, which we'll get to in a minute).
The actual difference in the lateral stresses on a curve caused by these differences in length (2.5", 3", 3.75")
in N Scale just doesn't seem like it would be much, especially if you have reasonable curves (mine at 18" and wider).
.....

I think the lighter car is at risk of pushing off the curve more easily than the heavier
ones and it doesn't really matter how long it is.   
It seems to me that 50 equally weighted cars would have less chance of
the light ones being "sprung" off the curve. 

I have no scientific proof.  It's just a gut feeling.

Thanks Max, fair enough. I suspect your gut is a pretty good analytical tool; I know I rely on mine a lot. I'm still experimenting, so time will tell, at least on my layout and under my operating conditions. Certainly, I'd err on the side of more weight on the short cars....

Thanks for your thoughts,
Otto

[Santa Fe Guy]

I wish my gut was still working as well as it did when I was younger:-)
Hi Otto, could be but I think it might come from your side of the pond. The web page for the "Deluxe Liquid Gravity"is www.deluxematerials.com  I believe it is mostly used in the model aircraft hobby. It comprises very very tiny balls and I have no idea what they are made of but it is heavy.
My SFRSD is almost flat. I designed it to run trains with two locos 12 cars and a caboose so I could work out good yards in the space I had available. Cars vary from 40 to 60 ft. I would like to run longer but.
Making sure my track work was as perfect as I could when building it, weighting all my cars just a tad over the MT standard, fitting 1015 MT trucks and couplers to all my cars one spring in one axle of each caboose and then changing to MT medium profile wheels makes for a pretty reliable RR. I'm getting old and do not see the point of changing to body mount in this stage of my life although I believe it would be better still.
I must admit the cars that cause the most issues are tank cars difficult to get the weight in them and low.
Rod.

[VonRyan]

So, how many cars are we talking about here? And what about the grade you mention? Do you have any problems with string lining?

I've never had a problem with string-lining. I don't have enough converted rolling stock to test the abilities of all but two of my locomotives. The only one I could test was my first-release Kato NW2 which pulled all 18 of my lightweighted Atlas 40' reefers (all with MT trucks and couplers) and brass N5c (with Bowser trucks and Atlas metal wheelsets) up a double S-curve with a 2% grade the whole way.
My Bachmann 4-6-0 tackled the same train (except with a bobber caboose) plus 4 stock Atlas reefers (I didn't have any more reefers to tack on at the time), but on a 2% curved-grade. I have yet to test the same train on a 2% double S-curved grade, but my suspicions are that it'll handle the train no problem.

[ChristianJDavis1]

I've never had a problem with string-lining. I don't have enough converted rolling stock to test the abilities of all but two of my locomotives. The only one I could test was my first-release Kato NW2 which pulled all 18 of my lightweighted Atlas 40' reefers (all with MT trucks and couplers) and brass N5c (with Bowser trucks and Atlas metal wheelsets) up a double S-curve with a 2% grade the whole way.
My Bachmann 4-6-0 tackled the same train (except with a bobber caboose) plus 4 stock Atlas reefers (I didn't have any more reefers to tack on at the time), but on a 2% curved-grade. I have yet to test the same train on a 2% double S-curved grade, but my suspicions are that it'll handle the train no problem.

To tie into what @VonRyan is saying, I operate by just about the same standards. I also remove any weight that is not integral (unless I cannot get into the car or dislodge the weight). Also as he states, the only problems I have ever had were due to factors other than the cars themselves (other than trip pins). I currently run a mix of trucks and wheels, ranging from standard MT's to vintage atlas trucks with the couplers swapped (scary prospect, I know). Just recently I had a Key M1a pulling a 40+ car train of mixed manufacturers and trucks. The micro trains cars remain with their original weight due to how they are weighted, but every other car has been lightened in some way, which makes a noticeable difference. The difference is most notable in my modern stock, which my crop of Kato engines would struggle with weight before I modified them. I cannot accurately report these seeing as o do not have a layout and rely on other's layouts and N-trak setups to do tests. The only problem I have seen with super light cars is that they do tend to go over easier (and together). Not bashing those who weight their cars, but I feel that the lighter the better (at least for me).

[jagged ben]

Two engines should be able to pull 50 cars.  And if that was the prototype, then the terrain must have been relatively level.  For roads that traversed mountains and valleys, such as in the northeast, more than two units were put on the point.

I have to disagree that it's possible with any given loco to pull the same number of cars on a model as the prototype would up a grade.   Granted, some of the grades I run on at the club are ridiculous.  (e.g. 3-5%).     But whereas a prototype might run 150+ cars over 2.5% grades with 10 units or less, you ain't gonna get that on a model unless the cars are very light, which in turn requires broader grades (to avoid string-lining) than most layouts will have space for.  In my experience you're gambling with more than 10 cars per locomotive on a grade like that and 21" radius curves, even if you run some as separately controlled helpers.  It's not so easy to avoid derailments, but it sure is interesting and fun! 

I should add that it depends on the locomotives, of course.  We have paradoxes such as that an N scale FT can pull as many or more cars than a Dash-9 because of the extra space to add weight inside the shell; in the real world the Dash-9 has three times the horsepower.     I really do like throwing my Athearn F45s into my 1980s consists because the extra pulling power means a longer train without looking it's like a power move.   So maybe if you are transition era you can get realistic loco/rolling stock ratios with less than realistic radii, but if you're a modern guy it ain't so easy.     And paradoxically (again), the trains are longer now than they used to be.    My final thought is just that when I get a train longer than 15' it starts to 'feel' to me like prototype length and this issue becomes more trivia, or rivet counting, or one-upsmanship, rather than about having a realistic scene.