I can’t remember a standard different from 2% in any discussion by ‘serious model railroaders’
My definition of free-rolling would involve much less ‘gradient’, but that’s immaterial to the actual question that was asked… and it would, in fact, involve testing the car on an incline rather than measure its impact behavior.
At the risk of opening more cans of besserwisser worms, perhaps there should be several measures of “free rolling”, including sensitivity to sustained ‘rolling away’ and enough inertia to facilitate ‘making the joint’ with Kadees even if the car would have run or recoiled away if the knuckles didn’t engage. There should be different and descriptive names for any such ‘metric’ to distinguish it from rolling resistance or drag.
I’m a licensed professional civil engineer. That means I sign and seal, and am responsible for, the plans for major projects completed under my supervision–and specifically that I can be sued for any mistakes because my job affects public safety.
Grade is NOT horizontal, but is defined as rise (or fall) divided by run. The only time grade is ever horizontal is when it is 0.00%. Gradient or gradiant in actual engineering practice is generally considered to be the EXACT SAME TERM as grade.
And NO those highway signs that warn you of a downhill grade are NOT talking about “rate of change of grade”, but literally that the downhill grade IS that average number expressed in percent and stated with or below the warning sign. The motorist doesn’t CARE if the grade is changing, they CARE how steep it is relative to braking capability of their vehicle (which is based upon conservative experimentally determined values for wet pavement that we use for real world design). Building a new Interstate freeway in rolling terrain? Your mainline grade cannot exceed 5% per federal standards (since they pay 80% of the cost).
Ruling Grade is defined as the grade over a division of a railroad (or highway) that represents the limiting design factor or tonnage restriction over that division. Ruling Grade is the grade upon which motive power tonnage tables (in both steam and diesel eras) are determined. How many and what types of engines per how many tons o
I completely agree. I have pushed kadee equipped cars down a siding with just the couplers touching. Yet they won’t couple. I love free rolling cars but there is or should be a limit to how free rolling a car can be. If I can push the car but not couple that is a problem.
We use grade to mean gradient. Technically grade is horizontal whereas gradient is the slope from one grade to another. A 2% grade is a 2% gradient but we modellers only mesh change of grade anyway.
Highway signs use grade in the same inaccurate manner andcwe all understand the warning means gradient or rate of grade change.
What are you talking about???
I’m a licensed professional civil engineer. That means I sign and seal, and am responsible for, the plans for major projects completed under my supervision–and specifically that I can be sued for any mistakes because my job affects public safety.
Grade is NOT horizontal, but is defined as rise (or fall) divided by run. The only time grade is ever horizontal is when it is 0.00%. Gradient or gradiant in actual engineering practice is generally considered to be the EXACT SAME TERM as grade.
And NO those highway signs that warn you of a downhill grade are NOT talking about “rate of change of grade”, but literally that the downhill grade IS that average number expressed in percent and stated with or below the warning sign. The motorist doesn’t CARE if the grade is changing, they CARE how steep it is relative to braking capability of their vehicle (which is based upon conservative experimentally determined values for wet pavement that we use for real world design).
There is a “maximum relative gradient” term which only a highway engineer would ever use, and it is expressed with the Greek letter delta. It is a unitless number because it represents the rate of change of one pavement edge line relative to another. It is a ratio and is used to calculate the required minimum length of superelevation transition between any two cross sections, or more typically between normal -2% cross slope and whatever the superelevation maximum rate is.
However, practically speaking most people mean grade whenever they say gradient. When doing superelevation calculations most civil designers will just refer to the required delta value rather than the full name given above.
Since we are mainly talking about trains, for railroad design purposes, they express superelevation in inches of elevation of the higher rail relative to the lower rail at a given point. Trackside observers will sometimes see the chalkmarks on the sides of the rails of recently laid track denoting the difference in inches.
I don’t quite understand this line of reasoning. First you state that weight does not matter, then you claim that heavier cars will roll farther. This latter claim is based on what? Did you do test runs, or is this just your expectation?
I was referring to heavy cars versus light cars, i.e. Adding weight to change the rolling characteristics. The complaint seemed to be the lighter cars accelerated “too quickly” implying that resulted from rolling resistance differences.
Anything can be misunderstood when taken out of context.
An earlier poster was “corrected” for referring to railroad slope as a gradient, which it is strictly speaking. A grade is a level not a slope. Hence concrete is referred to as being slab on grade, meaning level concrete.
Using the word grade to mean a slope is ambiguous since grade is a surveyed elevation. When the word grade is used to connote a slope it is technically an incorrect use, short for rate of change of elevation. All the construction drawings I see, and that’s a lot, have a reference elevation commonly referred to as the grade. The grading of construction lots is performed relative to grade sticks with grades written on them. The grader or excavator operator reads those as elevations he or she needs to achieve at that stake (well technically at the offset written onto the stake) which is a number referring to a horizontal elevation. The slope results from cuts or fills between these grade reference points.
Engineers commonly misuse (and misunderstand) ordinary English. I just finished reading a pipeline construction contract written largely by engineers. You can drive a truck through a lot of the verbiage. And I intend to.
The irony here is I was just offering the idea that maybe this forum might benefit from cutting people a little slack when they write posts. Maybe new contributors might stick around for longer. Just a idea.
I don’t have a bunch of numbers handy right now, but years ago I did a lot of testing and found that the following truck setup provided the most freerolling cars and best tracking.
Kadee self centering sprung (equalized) metal trucks.
Wheelsets replaced with Intermountain code 110 versions.
A drop of light oil in each journal box at assembly.
Cars weighted to NMRA RP or 10-15% less.
This combination inceased the pulling ablity of my locomotive fleet by 20-25% on average, and rolled free on .5% grades in most cases, performing better than ANY rigid plastic truck/wheelset combination I could find.
This discussion has become quite humourous at times. At one time the big quest was to get our anvils to move more efficiently. The hobby press was awash with complaints about the rolling, or non rolling qualities of HO trucks. At the time, it was blunt ended axles turning in bored holes. Then, along came Central Valley brand trucks. They were sprung, with metal wheelsets and more attention paid to the bearings. They were Cadillacs of their day, but bricks compared to today’s engineering plastic, needle point bearing gems. The complaints have done an about face. The trucks of today roll too much!
Before we go back to the days of square wheels under bricks, a simple solution to frisky running gear would be wipers of varying material and tension, bearing on the inner axles of one or both trucks. I, for one, don’t want to return to the days of sleds dripping 3-in-1 oil all over the place.
I was taught that when spotting cars, once they were “on spot”, before you pulled the pin, you made sure the hand brakes were set-tight. When you were picking up said cars, before releasing said handbrakes, you made sure you had made a good joint on the knuckles. Prevented lots of unnecessary excitement, cardio, and loud noises that way.
It would be very difficult to scale this down to HO for a few reasons:
One would need to have the exact same wheel profile in HO to have the exact same relative size of contact area between wheel and rail. There are “prototypical” profile wheels in HO, however:
Our HO wheels are normally some kind of a nickel plated finish riding on nickel silver rails. Both have different friction factors from prototype steel rails and cast or machined steel wheelsets.
Volume and especially weights of model freight cars may not replicate the real weights either empty or loaded.
Hmmm, I’m no engineer, but wouldn’t a heavier car that was rolling up a slight grade not roll so well…gravity pulling it the opposite direction, and by contrast, that heavier car would continue to roll farther down the slight grade? Both compared to a lighter car.
Not getting into physics math, but some portion of the roll is based upon the friction on the bearings and another based upon gravity pulling the mass towards the bottom of the grade.
And a heavier car would have more intertia needing to be broken, making it less free rolling, at least initially.
There isn’t much concern about free rolling unless you want to max-out the pulling power of the loco. JMO.
Inertia isn’t something needing to be ‘broken’; what you’re describing is static friction in the bearings, the thing that makes plain-bearing railroad cars hard to start but very close to rolling-element bearings in rolling resistance once the hydrodynamic wedge gets developed.
The point of higher inertia is that it reduces acceleration in ‘recoil’ when pushed, so couplers that need time to engage when pushed together will get it even if the car runs on jewel bearings with superfinished near-line-contact tread patches.
