Car weight, the NMRA standards, and my solution - Lighter weight is better!

[Y3a]

I experimented with car weights, and looking at the weights, what happens to the cars with NMRA weight standards on grades, and lighter than "standard", the actual physics of pulling cars up a grade and around super-elevated curves.

I model the N&W in the 1930's. I worked at a hobby shop in the 1980's and 1990's and bought a bunch of 2 bay hoppers, both Athearn and others. I kept the metal weights off the hoppers, BUT... replaced the plastic wheelsets with JayBee's. WHY you ask???? The ability of steam engines to pull is less than diesels mostly due to wheel diameters. I wanted to be able to pull AT LEAST 75 hoppers up a 3 percent grade without helpers with ONE 2-6-6-2 or 2-8-8-2.

BACKGROUND
I observed several model railroaders who over-weighted their cars to go up a 44" diameter super-elevated curve at 4 percent. many of the cars would lift the outer wheels as they went up the grades! Adding more weight won't fix this.

EXPERIMENTATION
I put 40 hoppers together with Jaybee wheelsets, and NO OTHER WEIGHT. I used the MDC trucks instead of the Athearn ones. I used a metal drill like tool to clean up the pockets and make sure of smooth rolling. I can easily pull 90 of the lightweight hoppers up a 4 percent grade with 28" diameter super-elevated curves. The lighter weight means the trucks will last longer and the weight is as low as it will go. These hoppers DON'T LIFT THE OUTSIDE WHEELS. You get the benefit of a great illusion as your engines pull almost twice the cars.

OK. So this is why I don't add weight to my cars anymore. Exceptions are cabooses which still need to be 3 - 5 times heavier so they can be pushed with a 2-8-8-2. It also allows teeny engines to pull 10 cars up a 4 percent grade.

Comments?

 

[fcwilt]

Thoughts:

Limit grades to 2 percent.

Solving one problem may create another.

 

[jwb]

I think the question is what you're trying to accomplish on a specific layout. On a smaller layout, I found that plastic wheels were OK, and I used the weights that came with Athearn, Accurail, Roundhouse, etc cars. When I began a larger layout, I found that "stringlining" on curves with grades was a problem. I replaced the plastic wheels with metal, which brought the center of gravity lower and improved rolling. This solved that problem in my particular case. The issue for the OP may be simply lowering the center of gravity and improving rolling. But I find that NMRA weight is a good compromise in my conditions.

 

[fcwilt]

But I find that NMRA weight is a good compromise

Exactly - it is a compromise - which is why I expressed my concern that solving one problem may create another.

 

[Espeefan]

It will work OK. I belong to a club so the weight is important. My stuff has to run with other peoples stuff so if cars are too light there are reliability issues. Everyone has their own requirements. I weigh per the standards.

 

[Iron Horseman]

The ability of steam engines to pull is less than diesels mostly due to wheel diameters.

Please explain what you mean by this statement. Are you talking about models or prototype or what?

I observed several model railroaders who over-weighted their cars to go up a 44" diameter super-elevated curve at 4 percent. many of the cars would lift the outer wheels as they went up the grades! Adding more weight won't fix this.

Why not? I would have to see the math on that one. The lifting of outer wheels is because the lateral force on the car is greater than the force of gravity holding it down. Since gravity on earth, the grade, car length, and the curvature are all constants you are saying that the additional downward force of gravity for delta mass x, is less than the lateral delta force of nx.

I put 40 hoppers together with Jaybee wheelsets, and NO OTHER WEIGHT. I used the MDC trucks instead of the Athearn ones. I used a metal drill like tool to clean up the pockets and make sure of smooth rolling.

I have contended for about two decades now that the NMRA weight standards were written when most cars rolled as well as a bicycle in sand, and need to be reconsidered. Today's equipment is so much better from the factory than things were "back in the day" even after they were tuned.

From a scientific stand point I think your experimentation is still lacking some controls before the blanket statements being made can be accepted at face value. I think weight might be much less a factor than all the other improvements you have made. MDC cars always rolled better than Athearn. Metal wheels have always rolled better than plastic. Truck frames have always needed to be honed for the needle point axles we put in them. How did the train go up the hill with each of those modifications done individually?

 

[DougC]

I think I've posted this info here before in more detail (too lazy to look), but for over 30 years in HO I've always ignored the "official" weight charts for HO model railroad rail cars - in my opinion there's just too darn much unneeded weight AND that weight interferes with the tracking (equalizing) of the railcars' trucks.

Anyway, my target weight for all my railcars (all of them 20' up to 54' long) is about 2.5 to 3 oz. each. (I think now they all average about 4 oz. each; I'm slow/lazy in converting all of them.) And when I feel like it I run my 3 63- to 70-car trains backwards around their respective 22" radius, 19" radius, and 16" radius L-shaped layout curves.

Do I get a derailment from time to time? Yes (mostly on the 16" curves.) How do I fix the problem? Move the car to another location in the train, or reverse it where it's at in the train, or put it in the yard and replace it.

For me it's kind of strange, amusing, satisfying, and yes a "little-on-edge" backing these long trains around fairly tight to very tight radius curves (especially when I can and once in a while do run them at half-throttle on an MRC power pack!) I know, it's crazy, but I've not had a train, engine or railcar yet dive off the layout to the floor. However, as info, I "fudge" here: When going in reverse at half-throttle speed [about 40 to 50 scale MPH] I only do one train at a time, and on the 16" radius curves I usually "chicken out" after 3 to 5 times around, and slow it down or change the train to forward direction. As a model railroader for 50+ years I've not yet completely run out of common sense.

DougC

 

[Y3a]

Please explain what you mean by this statement. Are you talking about models or prototype or what?

Both. Smaller diameter wheels will pull better than a loco with say 70" diameter (scale) drivers with both locos weighing the same.

Why not? I would have to see the math on that one. The lifting of outer wheels is because the lateral force on the car is greater than the force of gravity holding it down. Since gravity on earth, the grade, car length, and the curvature are all constants you are saying that the additional downward force of gravity for delta mass x, is less than the lateral delta force of nx.

Add in the damage the axles do to the heavy car, you will wear out the truck sideframes. I've actually seen this on several larger layouts. The damage also causes higher resistance which adds to the rising off the outer rails problem.

I have contended for about two decades now that the NMRA weight standards were written when most cars rolled as well as a bicycle in sand, and need to be reconsidered. Today's equipment is so much better from the factory than things were "back in the day" even after they were tuned.

TRUE DAT!

From a scientific stand point I think your experimentation is still lacking some controls before the blanket statements being made can be accepted at face value. I think weight might be much less a factor than all the other improvements you have made. MDC cars always rolled better than Athearn. Metal wheels have always rolled better than plastic. Truck frames have always needed to be honed for the needle point axles we put in them. How did the train go up the hill with each of those modifications done individually?

As I said, the heavier the car the more wear it adds to the sideframes and axle pockets. The illusion of a 70 ton hopper which is light as a feather makes for long trains up the grades. I model the N&W in the 1930's with many 2 bay hoppers and 24" min radius, super elevated at the top of the hill at 4%. Pulling 8-10 cars up tat grade with small brass 4-8-0's is what started this experiment. I started with leaving the weights out of a group of Westerfield and F&C kits. Still couldn't get up the hill with more than 7 cars. I then swapped in a lighter tender, but not much difference. switched to MDC trucks and JayBee wheels. Better. Reamed out the axle pockets and polished the insides with Graphite. Lots better. Then I did about half of my hoppers and reefers.

 

[Iron Horseman]

Both. Smaller diameter wheels will pull better than a loco with say 70" diameter (scale) drivers with both locos weighing the same.

I'm sorry but that really has little to do with the diameter of the wheels, the real deciding factor in your example is how the wheel is driven. From a physics stand point it comes down to what one would call in the vernacular "gear ratio". The diameter of the wheel is only 1 element of the ultimate power from motor to wheel ratio. In models that can easily be adjusted by changing the worm gear or spur gears in the drive line.

Add in the damage the axles do to the heavy car, you will wear out the truck sideframes. I've actually seen this on several larger layouts. The damage also causes higher resistance which adds to the rising off the outer rails problem.

That is a totally different thing. That is an effect over time. The blanket statement made did not have any "wear over time" factors in it. Assuming velocity is a constant, I still don't think that straight forward increase delta in F(grav) = gm is going to be less than the same delta in F(lat) = L/V where L is umm, umm, L = CV^2 (m^(1/2) cos(beta) * ((1 - rho ) tan(alpha) / (1 + rho) tan^2(alpha)). Hmmm, nope something not right there. I'm not certain the mass is the same "m" in both formulas, might be "M" instead. Besides this would be for tipping outward do to excess velocity not inward to to string-lining..... Ok all you civil engineers out there help us out. What would the string-lining formula be?

 

[Y3a]

Factor of adhesion. Smaller wheels have less contact to the rails so the weight is concentrated in a smaller point. Physics. The only thing that would improve the engines pulling power is sprung wheels/drivers. They keep better contact to the rails on uneven track, like going into a super elevated curve. Since all model RR model that run on electricity use gears, worms chain drives etc the drive systems have little to do.

 

[fcwilt]

Factor of adhesion. Smaller wheels have less contact to the rails so the weight is concentrated in a smaller point. Physics.

But friction is a function of (among other things) force and surface area.

 

[Iron Horseman]

Factor of adhesion. Smaller wheels have less contact to the rails so the weight is concentrated in a smaller point. Physics.

That gets back to the point of my original question of the scope of your statement. If you were talking about prototype or models. Adhesion is a huge issue with the prototype. I find it very hard to believe that the difference in adhesion in HO scale between a 40" wheel and a 33" wheel (or even a 70" wheel) is going to make any practical measurable difference. Once again I'll believe it when I see the math.

 

[tootnkumin]

'Tis an interesting subject this, because unless metal wheels and rails are capable of compression (like rubber car tyres), theoretically, there should be no difference in the "contact patch" size, regardless of diameter. So does metal compress (distort and reform) under the sorts of loads imposed by HO scale engines and rolling stock?

 

[Y3a]

I have weighted all my brass and Bowser steam engines. Brass and The "Powerhouse Series" of 2-8-8-2's from Oriental Ltd have sprung drivers. I added as much weight as was possible and swapped the springs for heavy duty ones since I was also verifying driver quarter and had the mechanics apart anyway.

I have a very rare Hazelton "Auto-Quarter" tool which is a very precision device for quartering, gearbox replacement and such. This tool has made all my steamers run very smooth, even the Bowser ones.

The Bowser Challenger is the heaviest loco I own. It tilts at about 2.75 pounds! No plastic bridges for that puppy! It also pulled 130 cars on a club layout! I also have a 2-6-6-2 in brass (N&W Z1a) which was the first to get the max weight and heavy duty springs and it can pull 80 cars and it weighs a little under 2 pounds. It has them little 56" drivers too. As far as the metals compressibility (GREAT QUESTION BTW) I think the rail might just be! What is the exact metal formula they used in the steam era for the rail, and how different is it to Atlas Code 83 or Code 100?

My original point, through playing around on my own layout was that for me lighter, smoother rolling cars allowed me to pull more hoppers up the hill which looked more realistic. My BLI Y6b (stock) has limits of 35-37 hoppers up a 3% grade, and only about 26-27 up the steeper 5% grade. A "Powerhouse" 2-8-8-2 can pull the same, but it has sprung drivers and extra weight. The experimentation has had some drawbacks as the little Sunset 4-8-0's really don't have enough boiler to fill with lead sheet to get them to pull as good as I want, so I may have to double head them up that 5% grade with 12-15 cars.

Just a side note (since 3 of my model RR buddies also have been discussing this) I clean the track with a a gondola with the bottom cut out and a block of wood with a Walthers Bright Boy glues to the bottom and mag wheel weights stuck on top pulled around with 2 Athearn Trainmasters (weighted too) They go around the main lines for about 20 minutes each direction (north and south) while I use another Bright Boy to do the yard and other sidings. I clean the track every 3 weeks...just because.

 

[tootnkumin]

I admit to being a bit facetious with my question, but yes, the lighter the load being pulled and the heavier the loco doing the pulling, will make a difference. Free rolling axles and smooth wheels will probably have as much effect on inertial resistance as weight. Sprung axles will also help where there may be uneven, out of level joints between rail ends in maintaining traction, but those will also interfere with the following rolling stock. So, good trackwork and well maintained equipment and enough power to weight ratio is a necessity for not only us modellers, just as it is for the 1/1,s. So stick a couple of helpers in the middle and watch them rip.

 

[D&J RailRoad]

I think I've posted this info here before in more detail (too lazy to look), but for over 30 years in HO I've always ignored the "official" weight charts for HO model railroad rail cars - in my opinion there's just too darn much unneeded weight AND that weight interferes with the tracking (equalizing) of the railcars' trucks.

Anyway, my target weight for all my railcars (all of them 20' up to 54' long) is about 2.5 to 3 oz. each. (I think now they all average about 4 oz. each; I'm slow/lazy in converting all of them.) And when I feel like it I run my 3 63- to 70-car trains backwards around their respective 22" radius, 19" radius, and 16" radius L-shaped layout curves.

Do I get a derailment from time to time? Yes (mostly on the 16" curves.) How do I fix the problem? Move the car to another location in the train, or reverse it where it's at in the train, or put it in the yard and replace it.

For me it's kind of strange, amusing, satisfying, and yes a "little-on-edge" backing these long trains around fairly tight to very tight radius curves (especially when I can and once in a while do run them at half-throttle on an MRC power pack!) I know, it's crazy, but I've not had a train, engine or railcar yet dive off the layout to the floor. However, as info, I "fudge" here: When going in reverse at half-throttle speed [about 40 to 50 scale MPH] I only do one train at a time, and on the 16" radius curves I usually "chicken out" after 3 to 5 times around, and slow it down or change the train to forward direction. As a model railroader for 50+ years I've not yet completely run out of common sense.

DougC

That would make a good video that I'm sure a lot of people would enjoy seeing.

 

[tootnkumin]

Hey Doug! Ever considered a loop the loop?

 

[wright2626]

i believe that particular cars want certain weights to run well. some need very little weight, while others need a little more.

 

[DougC]

Hey Toot, you wascal (aka Serial Kidder), I had to google "loop the loop" to find out what it is. They say it's a verticle loop. Yes, I can do this with marbles and a marble run, but I'm afraid I might have to do a "little" more thinking to get my SD40-2s to do vertical loop-d-loops. Thanks for the (ahem) challenge.

DougC

 

[tootnkumin]

Hey Toot, you wascal (aka Serial Kidder), I had to google "loop the loop" to find out what it is. They say it's a verticle loop. Yes, I can do this with marbles and a marble run, but I'm afraid I might have to do a "little" more thinking to get my SD40-2s to do vertical loop-d-loops. Thanks for the (ahem) challenge.

DougC

Just need a bit o' hotting up and 24volts.