The term “free rolling” has been used repeatedly in MR arictles and I thought I had once seen a definition but a search of trains.com just now returned only articles that use the term without an objective definition. My memory says free rolling was once defined as the gradient when a car begins to roll when released. My questions here is, “What is that gradient?” I would think it’s somewhere in the neighborhood of 1 or 2 percent. Does anyone have a better number?
My cars with Kadee or Accurail trucks and Intermountain or Tangent wheelsets roll if the track is not perfectly level. They roll when the gradient is not perceptible just by looking at the track. To see the gradient you need a level or one of those cars…
I remember it as being 2%. These days a “free rolling” car will do a lot better than that.
Hello All,
I run cuts of upgraded Tyco 34-foot operating hoppers from the 1970s.
The upgrades are:
- Intermountain Semi-Scale (0.088 tread width) Metal Wheel Sets
- Accurail Plastic Roller Bearing trucks
- Body mounted Kadee #5 coupler
I use a Micro-Mark HO Truck Tuner to ensure the bearing surfaces are burr-free and at the NMRA RP of 60º.
These cars are underweight at 3 oz each when empty (NMRA RP weight is 3.34 oz or 95 g).
My 4’x8’ pike has a less than 1% grade (0.96%) along the 8-foot side because it sits on the bed in the computer/train/spare bedroom.
This is measured with a Micro-Mark digital level.
If I let a cut of eight (8) cars go at the top of the “grade” they will free-roll and settle in the middle of the curve at the bottom of the grade.
This is on a straight section of track 50-inches long to the asymmetrical curve of 18- and 15-inch sectional track.
Hope this helps.
I also run those old Tyco cars. Mine are from the early 1960s, certainly pre-65 when I graduated from high school. I have also replaced first the Talgo couplers with body-mounted Kadees, and then the trucks and wheelsets with Tichy trucks and Intermountain wheelsets.
The string of cars used to take a pair of engines to pull around, but it’s down to one engine after the wheelset upgrade.
I try to maintain a zero grade on my layout, but since I went to all-metal wheels I’ve found a few sidings where I was careless and had to add some tall grass between the ties to keep cars from rolling downhill.
Mr Beasley
Thanks for the tip about adding tall grass between the ties. That sounds like a very clever and not obvious way to deal with a siding that is a bit off level. I have this problem and love this solution. Thanks.
wdcrvr
Unfortunately, I can’t give credit where credit is due, but I started to “tune” my rolling stock after reading an article some years ago, which explains my hazy memory, in the RMC.
The author set his own standard of “free rolling” at a 3% grade. At that time I made my test track for both 2% and 3%, and strive for 2%, but generally don’t sweat it if I only achieve free rolling at 3%.
Test track by Bear, on Flickr
Test Track1 by Bear, on Flickr
[2c] Cheers, the Bear.[:)]
The better cars today (NOT “upgraded” Tyco) will start rolling for me on my 0.4% grade. I’ll call that free-rolling.
Also, some manufacturers (including but not limited to Exactrail) advertise cars as being free rolling when in fact they are anything but. So I take that term with a grain of salt.
John
Wouldn’t “free-rolling” be defined as the gradient on which the piece of equipment in question begins to roll, without motive power? As stated, depending on many factors, the same pieces of rolling stock, from the same manufacturer will require different percentages of gradient to begin independent movement.
The term “free rolling” appeared frequently in advertisements and reviews, without any specific percentage of gradient ever being mentioned. It could be 0.4% as mentioned for some of the upgraded Tyco hoppers, or 14% for a straight-out-of-the-box example of the same car. A lot of modelers found out their layouts were not as flat as they thought, when they began using Lindbergh trucks, way back when.
i believe “grade”, not gradient is the appropriate term
after noticing that some cars seemed to roll up hill, i checked each of my car’s trucks on an adjustable grade, “tuning” those that required more than a 2% grade to roll on there own.
some trucks easily rolled on far less than 2%. others required work to roll at 2%
we measured the pulling force of a loco with a string so cars on level track but thru some turnouts. there were ~30 cars we estimated at weighing ~4 oz/car. we measured ~2.4 oz of force which works out to be roughly 2%.
My latest “free rolling” cars will move if you simply breathe in their vicinity, and rapidly run away if you give them a funny look…
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 and we all understand the warning means gradient or rate of grade change.
Mine too. Terrible for switching. It tends to just bump the car down the spur. I need to replace free rolling trucks with old Tycos or something…
I do recall a siding on our railroad that required quite a bit of work before cars stopped rolling out toward the mainlne switch.
The bump and run syndrome disappears if you are switching cuts of cars, rather than an individual car. It may also be a signal that you need to free up some couplers to guarantee the knuckles open and they center correctly.
It also depends upon how fast, or not, the cars are banged.
I’ve taken to over-weighting the cars in my roster that I can, and all of my Accurail kit builts are true “heavy weights” with added weights inside them.
When I delivered auto parts, my boss and coworkers thought I was nuts that I asked to purchase a box of wheel weights, as I do not have a tire mounting/balancing machine. But the cost was way less than the cost of similar weights available from the model companies.
While they still roll very smoothly with the added Intermountain wheelsets, they tend to not “take off” when slowly switching industries. (So long as I don’t bump hard…)
This drives me absolutely nuts. The cars jump because they have so little resistance. I have almost replaced the wheelsets with something with more resistance because of it. The cars follow the gradient more readily than my switchers force. That my freinds is free rolling!
Adding weight to a free rolling car won’t change how far it rolls after being pushed by a locomotive during shunting. In fact, given that bearing and wheel friction is unlikely to be proportional to weight of the car, heavier cars will roll further if hit at the same speed by the locomotive. In theory friction is merely a coefficient but in practice friction forces come from several sources not always obvious. The friction developed by the sole of your shoe on the ground is basically proportional to weight placed on the sole. For a bearing things are not so simple. For a rolling wheel the friction is developed mainly within the axle bearing.
That’s one reason we know Galileo didn’t actually drop an iron cannonball and a hollow iron sphere of the same volume from the tower of Pisa…
The way I was taught is that ‘gradient’ is the measurement and ‘grade’ is the physical thing. I have never seen the expression ‘ruling gradient’ and never expect to because ‘grade’ encompasses both the gravitational and curve resistances in the expression “ruling grade”.
Of course when the civil part of the roadbed has no gradient we just call it ‘level grade’ just as the ‘grader’ left it… [:-^]
Maybe there are parts of Canada where they sing ‘She was going down gradient makin’ 145 kilometers an hour when they heard that whistle scream…’
There seem to be several who have more time to discuss the semantics of the responses rather than addressing the point of the question.
The way we defined “free rolling” 40 years ago when the club was testing cars to make sure they met the club’s standard was to place it on a tilted board that sloped up 2 inches in every 100. And that 2% was what I think was thrown around in the press. I know we didn’t create that value. There was not ever any discussion as to whether this was grade, slope, gradient or any of the other felgercarbis that some want to throw around.
And there was not any “pushing” involved, either by 0-5-0 or powered engine. The car was simply placed at the top of the hill and the 0-5-0 released. The car either rolled (passed) or didn’t (failed).
I know from experience that it is easier to couple to a heavy free rolling car than a light one. This is because the lighter car will want to run away from the coupler before the mechanical forces causing the coupler to remain closed can be overcome. I think this is called “inertia”.
I also believe that a heavy free rolling car will roll further than a light one. When we balanced turbine rotors the heavy rotors always took longer to coast down from full speed than the light ones. Again, I think this was inertia.
So far as Galileo goes, I don’t know what he dropped on his Pizza, but I do know that he didn’t get it from Papa Johns.