While at one of my favorite train watching spots this afternoon, a UP auto rack train passed by. All the auto carriers had stenciled on the side of the car, near the bottom and close to the truck, 28" inch wheels. Why is this information stenciled on each car? What is the significance of 28" wheels?
Rio Grande Valley, CFI,CFII
28 inch wheels are of a smaller diameter than other normal freight car wheel. Freight car wheels range for the 28 inch up to (I think) 40 inches in diameter. The normal freight car wheel is 36 inches in diameter.
Putting the wrong diameter wheel set into a cars sets in motion a whole lot of geometrical problems that can end up in a derailment.
Never too old to have a happy childhood!
BaltACD 28 inch wheels are of a smaller diameter than other normal freight car wheel. Freight car wheels range for the 28 inch up to (I think) 40 inches in diameter. The normal freight car wheel is 36 inches in diameter. Putting the wrong diameter wheel set into a cars sets in motion a whole lot of geometrical problems that can end up in a derailment.
Would one of the reasons for the smaller wheel be to lower the height of the car for clearance purposes?
PJS1 BaltACD 28 inch wheels are of a smaller diameter than other normal freight car wheel. Freight car wheels range for the 28 inch up to (I think) 40 inches in diameter. The normal freight car wheel is 36 inches in diameter. Putting the wrong diameter wheel set into a cars sets in motion a whole lot of geometrical problems that can end up in a derailment. Would one of the reasons for the smaller wheel be to lower the height of the car for clearance purposes?
Most certainly! Want to make some convertibles - put some 36 inch wheels in place of 28 inch wheels. 20 foot 2 inch high car becomes 20 foot 6 inches.
Dropping the center of gravity and dropping car floor height in ramp operations also figures into it.
don't smaller wheels have a lower max axel load ?
Why? The axle, same diameter, just spins a little faster. The wheels tend to have a just slightly beefier cross section with the same tread.
I wouldn't be as worried about the axle as I would be about the contact surface of the rail. Seems to me that the smaller wheel would have a smaller contact patch (fore/aft) than a larger wheel and lead to higher contact pressure for a given axle load.
One reason for the stenciklikng is to insure repairs are made properly. If larger wheels were substitiuted, there would be a coupler height problem, possibly othe problems such as clearances.
Yes, small wheels have less load carrying capacity. In recent years common freight car wheels are as follows: 28" wheels, 55 ton capacity, used with 6 X 11 bearings; 33" wheels, 70 ton capacity, used with 5 X 9, 5 1/2 X 10, and 6 X 11 bearings; 36" wheels, 100 ton capacity, used with 6 1/2 X 12 bearings; 38" wheels, 125 ton capacity, used with 7 X 12 bearings. The nominal capacity of a wheel is determined by both its ability to carry the weight of the loaded car and its ability to dissipate heat generated in braking. 28" wheels are used on low deck 89' flat cars intended to be used with tri level auto racks. These cars should have a star by the load limit stenciled on the car, which indicates that the load limit is not determined by the journal size. Getting the wrong size wheel set in a truck is unlikely. The truck design and castings are designed for specific wheel sets. They would just not fit.
Thanks to all for the insightful and helpful information.
To stray a bit, what would be the size of the wheels on Amtrak's Superliner cars?
PJS1what would be the size of the wheels on Amtrak's Superliner cars?
The GSC-G70s have nominal 36", but that doesn't account for wear. At least one 110-mph design started with 36.5" nominal to keep the performance closer to 36" over the wear life of the wheels.
I think the MD-70s (which are European) may have been delivered with 914mm wheels (which DOT indicates are nominally equivalent to 36.0")
Since it is so infuriating to find meaningful information on Superliner wheels on the Web, I refer you directly to DOT 11695-DS1 (which probably has all the detail you'd want on either truck design).
https://rosap.ntl.bts.gov/view/dot/11695/dot_11695_DS1.pdf
WARNING if you thought the fluidized-bed boiler patent was TMI...
David1005 The nominal capacity of a wheel is determined by both its ability to carry the weight of the loaded car and its ability to dissipate heat generated in braking.
The nominal capacity of a wheel is determined by both its ability to carry the weight of the loaded car and its ability to dissipate heat generated in braking.
I've wondered about the latter in the past, particularly after reading the report on the Sand Patch runaway (due to brake fade from overheated wheels). A larger wheel would have more area to dissipate heat at the cost of being heavier than a smaller wheelset.
erikemI wouldn't be as worried about the axle as I would be about the contact surface of the rail. Seems to me that the smaller wheel would have a smaller contact patch (fore/aft) than a larger wheel and lead to higher contact pressure for a given axle load.
- PDN.
Paul_D_North_JrHowever, I suspect the axle load for a tri-level is fairly light.
Would explain why long strings of racks never seem to have many units on the front end while they're passing at a good clip.
Paul_D_North_Jr However, I suspect the axle load for a tri-level is fairly light. As a 'first approximation' (guess), 3 levels x 5 cars per level x 2 tons per car = 30 tons per car, spread over 2 trucks - plus the tare weight of the car and the rack. Even one of those articulated ocars with a common center truck - essentially 30 tons on that 1 truck - wouldn't be challenged all that much. It would be interesting to see what the actual weights are from someone who knows.
However, I suspect the axle load for a tri-level is fairly light. As a 'first approximation' (guess), 3 levels x 5 cars per level x 2 tons per car = 30 tons per car, spread over 2 trucks - plus the tare weight of the car and the rack. Even one of those articulated ocars with a common center truck - essentially 30 tons on that 1 truck - wouldn't be challenged all that much. It would be interesting to see what the actual weights are from someone who knows.
Paul,
That's close to what I would estimate for loading. While cars are still primarily made of steel by weight, they are pretty much air by volume. 30 tons per truck translates into an axle loading of 15 tons, well below the 33 - 38 tons for many RR cars. My contention was that while the axles on a 28" wheel set might be able to handle 33 tons, I wouldn't be so sure of the contact surfaces. For a 15 ton axle loading, the 28" wheels would likely have a lower peak contact pressure than a 36" wheel with a 33 ton axle load.
A 28" wheel set should be lighter than a 36" wheel set and the reduction in unsprung mass should improve ride quality.
- Erik
Erik -
I recall seeing the metric expressed as something like tons of axle load per inch of diameter, someplace or another quite a few years ago. Now that I think about it, probably by John Kneiling - he often discussed wheel & axle sizes for the lighter loads of his integral train systems.
Maintaining that ratio - though probably not quite so linear for the contact area size - would go a long ways towards adjusting the axle load to match the wheel diameter, since the circumference is linear with diameter (C = D x pi, 3.14) [I know you know this - I'm just going into the details for those who might not]. For example, 33 tons on a 36" wheel = 0.92 tons/ inch diameter; 28" x 0.92 = 25.7 tons > 15 tons hypothetical.
P.S. - Edited the last line 8-04-2018 to correct the < to >
Smaller wheels do lower the car’s profile as well as its carrying capacity. That’s why you don’t see them on 100 ton + capacity cars and you do on high cars. Stenciling wheel size on a car seems unnecessary as would think anyone responsible for changing or installing would know without it. In our age of graffiti much of what’s stenciled on a car is obliterated anyhow.
F.S. AdamsSmaller wheels do lower the car’s profile as well as its carrying capacity. That’s why you don’t see them on 100 ton + capacity cars and you do on high cars. Stenciling wheel size on a car seems unnecessary as would think anyone responsible for changing or installing would know without it. In our age of graffiti much of what’s stenciled on a car is obliterated anyhow.
Never underestimate the abilities of one to misunderstand what is actually required.
BaltACD F.S. Adams Smaller wheels do lower the car’s profile as well as its carrying capacity. That’s why you don’t see them on 100 ton + capacity cars and you do on high cars. Stenciling wheel size on a car seems unnecessary as would think anyone responsible for changing or installing would know without it. In our age of graffiti much of what’s stenciled on a car is obliterated anyhow.
F.S. Adams Smaller wheels do lower the car’s profile as well as its carrying capacity. That’s why you don’t see them on 100 ton + capacity cars and you do on high cars. Stenciling wheel size on a car seems unnecessary as would think anyone responsible for changing or installing would know without it. In our age of graffiti much of what’s stenciled on a car is obliterated anyhow.
PJS1 BaltACD F.S. Adams Smaller wheels do lower the car’s profile as well as its carrying capacity. That’s why you don’t see them on 100 ton + capacity cars and you do on high cars. Stenciling wheel size on a car seems unnecessary as would think anyone responsible for changing or installing would know without it. In our age of graffiti much of what’s stenciled on a car is obliterated anyhow.
Let's keep everything on a need to know basis and no one needs to know.
H.L. Mencken's (from Baltimore) actual quip on this was: “No one in this world, so far as I know — and I have searched the records for years, and employed agents to help me — has ever lost money by underestimating the intelligence of the great masses of the plain people. Nor has anyone ever lost public office thereby. The mistake that is made always runs the other way. Because the plain people are able to speak and understand, and even, in many cases, to read and write, it is assumed that they have ideas in their heads, and an appetite for more. This assumption is a folly."
Be careful to keep this separate from P.T. Barnum's
I conflated those two for many years because professors I trusted had said the quote was 'You'll never go broke underestimating the taste of the American public" -- which you'll confess has the proper Balimerean snarl...
I think Ambrose Bierce was the master of acerbic cynicism, even more so than Mencken. (from The Devil's Dictionary):
charlie hebdo I think Ambrose Bierce was the master of acerbic cynicism, even more so than Mencken. (from The Devil's Dictionary): Idiot, n. A member of a large and powerful tribe whose influence in human affairs has always been dominant and controlling. The Idiot's activity is not confined to any special field of thought or action, but "pervades and regulates the whole." He has the last word in everything; his decision is unappealable. He sets the fashions and opinion of taste, dictates the limitations of speech and circumscribes conduct with a dead-line.
Is he orange?
Greetings from Alberta
-an Articulate Malcontent
OK, I've never found a reasonable answer to this question. Heck Fire, I worked for a carbuilder (Thrall) and couldn't get a response. It was too far "Out There".
What's magic about the two axle truck? If the wheel bearing surface weight is a problem, why not use more wheels? As in a three axle trucks under heavy loads. The freight car's carrying capacity could increase while the number of expensive components could be reduced. For example, there would be fewer brake valves and couplers required to move the same amount of tonnage. These components all require maintenance and reducing their number will also reduce maintenance cost.
Is there a logical reason heavy loads such as oil, sand, coal, ore, grain, etc., can't move more economically on three axle trucks?
greyhoundsWhat's magic about the two axle truck? If the wheel bearing surface weight is a problem, why not use more wheels? As in a three axle trucks under heavy loads. The freight car's carrying capacity could increase while the number of expensive components could be reduced. For example, there would be fewer brake valves and couplers required to move the same amount of tonnage. These components all require maintenance and reducing their number will also reduce maintenance cost. Is there a logical reason heavy loads such as oil, sand, coal, ore, grain, etc., can't move more economically on three axle trucks?
The magic of the three-piece truck is that its pieces can be made very strong and reliable for a minimum of components. Even a 'simple' three-axle version (which is what the Buckeye truck is) requires 'handed' sideframes, knuckles for the arrangement around the center axle, and a bolster arrangement with different side-bearing locations than three-piece trucks use.
There was, in fact, an organized effort to develop and sell a three-piece truck back around the turn of the century, when HAL to 315,000# looked as if it would produce more track damage than would be tolerable. The very fact that it is so hard to find information on this, or even who currently holds the patents to it, should tell you the perceived market for three-axle freight trucks at present.
Yes, one of the selling points was that six smaller wheels had the load-bearing capacity of four bigger ones, so the envelope of the cars using them could be larger and still fit reasonable plate limits.
duplicate
SD70Dude charlie hebdo I think Ambrose Bierce was the master of acerbic cynicism, even more so than Mencken. (from The Devil's Dictionary): Idiot, n. A member of a large and powerful tribe whose influence in human affairs has always been dominant and controlling. The Idiot's activity is not confined to any special field of thought or action, but "pervades and regulates the whole." He has the last word in everything; his decision is unappealable. He sets the fashions and opinion of taste, dictates the limitations of speech and circumscribes conduct with a dead-line. Is he orange?
Hard to believe that was published in 1906. Apparently Bierce wasn't just a cynic; he could see into the future.
Paul_D_North_Jr Erik - I recall seeing the metric expressed as something like tons of axle load per inch of diameter, someplace or another quite a few years ago. Now that I think about it, probably by John Kneiling - he often discussed wheel & axle sizes for the lighter loads of his integral train systems. Maintaining that ratio - though probably not quite so linear for the contact area size - would go a long ways towards adjusting the axle load to match the wheel diameter, since the circumference is linear with diameter (C = D x pi, 3.14) [I know you know this - I'm just going into the details for those who might not]. For example, 33 tons on a 36" wheel = 0.92 tons/ inch diameter; 28" x 0.92 = 25.7 tons < 15 tons hypothetical. - PDN.
Maintaining that ratio - though probably not quite so linear for the contact area size - would go a long ways towards adjusting the axle load to match the wheel diameter, since the circumference is linear with diameter (C = D x pi, 3.14) [I know you know this - I'm just going into the details for those who might not]. For example, 33 tons on a 36" wheel = 0.92 tons/ inch diameter; 28" x 0.92 = 25.7 tons < 15 tons hypothetical.
Wheels have to comply with AAR Specification M-107/ M-208. www.wheels-world.com/UploadFiles/standard/AAR_M-107_M-208-2009%20%20Wheels,Carbon%20SteeL.pdf
The wheel loads are on page 31.
I tried to post just a Word table with just the loads, but the editor doesn't transfer it to the post.Regards, Volker
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