In several recent threads the topic of sprung trucks and various brands of wheelsets once again was discussed.
I have gathered some engineering information in an attempt to explain how model trucks actually work, why some roll better than others, why equalization matters, and hopefully dispel a few myths.
Myth #1 - The car rides on the points of the axles.
Myth #2 - Our cars do not weigh enough to make sprung trucks "equalize".
Myth #3 - Rigid trucks track just as well as equalized trucks.
First, some basic engineering standards for model trucks and their components, from the NMRA:
Interestingly, the axles on Intermountain wheelsets are nearly identical to the design shown above.
The key feature being the small axle diameter outside the wheel, resulting in a smaller axle cone.
Well no, actually the cone of the truck journal contacts the cone of the axle tip, but not on the "end" or point of the axle, but rather like this:
Notice from the NMRA specs that the journal cone is 60 degrees minimum, while the axle is 50 degrees maxinum and the max axle length is less than the minimum journal span, creating a minimum standard for side to side play. Interestingly there is no maximum spec for side to side play.
It is assumed that as long as the axle stays in the truck, gravity will center the axle.
This leaves a 5 degree difference on the weight bearing top side to minimize the contact patch of the axle onto the journal.
Varying amounts of side play are allowable, but the axle points are not all the way into the points of journal cones, so the load is not on the axle tip, but on the side of the axle tip near the point.
Well, here is the thing, your freight car does not need to actually compress the springs in sprung trucks, in fact there is no expectation that the springs will provide that sort of "suspension".
We don't need that. But what we need is equal loading of the car weight onto all the wheels, typically 8 of them on a freight car.
For that the to happen the only thing that the truck needs is independent flexing of the sideframes at the truck bolster. The springs allow this and very little weight is required to cause this flexing.
Each sideframe needs to move as the red arrows indicate, one end up as the other end moves down, the springs need only compress the smallest amount while still holding the top of the bolster in contact with the sideframe - which is unlike the prototype.
Rigid trucks track "OK" for most peoples needs, no question.
BUT, equalized trucks track better. They will navigate grade transitions better, work better on super elevation with less chance of string lining, and result in smooth running and less slack action because the "dynamic friction load" will not change as much as track conditions change.
All this is pretty small numbers wise - until - your trains get longer, 30 cars, 50 cars, 100 cars.
Much of the time, with rigid trucks, the actual weight of your fright car is only on 6 wheels. No different than a chair on an uneven surface.
Equalized trucks also travel thru turnouts better because no wheels are ever "floating". Those wheels that might be floating on a rigid truck can more easily ride up on frogs and points.
Why do the Intermountain wheelsets work so good?
Why do the Kadee sprung trucks roll OK, but not great?
Why does the Intermountain wheelset fix this?
The sideframes of a sprung or equalized truck have to move relative to the axles, this changes the relationship of the axle to the journal - some would say this is justification for the rigid truck and "settling" for the 6 wheeel effect.
Kadee, and many others use a large cone axle rather than the small cone in the NMRA Recommended Practices.
They look like this:
As the sideframe moves, the larger cone has more surface area that can come in contact with the journal cone, with more friction and more opportunity for binding.
Admitedly this is less of a concern with rigid trucks, but tests show, and owners report, that small axle wheelsets like Intermountain work better even in rigid trucks.
Here is a photo of the Intermountain axle end (right) vs the Kadee axle end (left):
I started in this hobby at a time when most better equipment came with sprung trucks, and names like Kadee, Central Valley, Lindberg, Walthers and Silver Streak were synonymous with quality sprung trucks. That was 54 years ago.
Today, and for the last two decades, I have been refitting Kadee sprung trucks with Intermountain wheelsets to achieve the most free rolling equalized truck possible.
The goal - derailment free operation of trains in the 40 to 70 car range.
Another side benefit, the weight of metal trucks adds weight where it works the best, down low at the track. Often making it unnecessary to add additioanl weight even the cars are slighty below NMRA recommended practice.
Questions and comments welcomed.
Sheldon
Wow, Sheldon, you put a lot of work into this! You make a good arguement for Intermountain and Kadee (equalization), And the two combined together. And, cleared me up on Myth #1.
Running about 15 car trains on my layout doesn't push my trucks limitations enough to sweat it. But I have a string of IHC ore cars that have a lot of drag, despite using a truck tuner and metal wheelsets. I'll have to see if intermountains will help those. Thanks for the work. Dan
ATLANTIC CENTRALMyth #2 - Our cars do not weigh enough to make sprung trucks "equalize". Well, here is the thing, your freight car does not need to actually compress the springs in sprung trucks, in fact there is no expectation that the springs will provide that sort of "suspension"
Well, here is the thing, your freight car does not need to actually compress the springs in sprung trucks, in fact there is no expectation that the springs will provide that sort of "suspension"
As well as HO and On30 I also have some G scale, and there at least some cars do indeed weigh enough to compress springs a bit.
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
Sheldon, well done! It is great to see a definitive explanation on this from an expert with experience and (icing on the cake) the information to back it up. Thank you.
Mike
Gidday Sheldon, thanks for putting in the effort. In MY bigger picture, I guess it really doesn’t matter, but my initial thought is, does the smaller bearing surface of the Intermountain axles cause any more wear to the bearing surface of the trucks? Cheers, the Bear.
No, because under "ideal" conditions the contact patch is the same size with both types of axle. And the weight vs hardness is not really a wear issue of much concern.
It is only as the sideframe moves during equalization that the larger axle is more likely to have more contact, and thereby more friction, and more possiblity for binding.
If, as in my case using Intermountain wheels in Kadee trucks, you have metal to metal, some form of lubrication is desirable.
I use a small drop of light oil. It soaks into the porous cast metal of the sideframe journal and acts like an oilite bearing, not needing relubrication for many years, and causing no issues commonly believed about lubricating trucks.
If either the axle of journal are slippery plastic, wear concerns are even smaller.
KitbashOn30 ATLANTIC CENTRAL Myth #2 - Our cars do not weigh enough to make sprung trucks "equalize". Well, here is the thing, your freight car does not need to actually compress the springs in sprung trucks, in fact there is no expectation that the springs will provide that sort of "suspension" As well as HO and On30 I also have some G scale, and there at least some cars do indeed weigh enough to compress springs a bit.
ATLANTIC CENTRAL Myth #2 - Our cars do not weigh enough to make sprung trucks "equalize". Well, here is the thing, your freight car does not need to actually compress the springs in sprung trucks, in fact there is no expectation that the springs will provide that sort of "suspension"
Yes, as you get into larger scales, the physics move closer to the prototype.
And equalization can become that much more important.
Well done, Sheldon, and quite convincing!
Takeaways: Sprung or equalized trucks are superior to rigid trucks. Intermountain metal wheelsets are the best wheelsets. Any other takeaways to note?
Rich
Alton Junction
Good info for novices!
Rio Grande. The Action Road - Focus 1977-1983
When I was in Scale Rails Of Southwest Florida, we had a demonstration board showing why sprung trucks (HGC did not exist yet) were required on all cars that ran on the club layout.
It was just a piece of flex track with a couple of staples over the track. Rigid trucks would always derail, but a string of freight cars with sprung trucks would glide right through the obstacles.
The fact is that when a sprung (equalized) truck has one wheel lifted, the other three stay on the rail. When a rigid truck has one wheel lifted, another wheel is also lifted, and there is a derailment.
Great work on the post Sheldon. THANK YOU!
-Kevin
Living the dream.
Very good discussion. This ought to be a 'sticky' somewhere...
I want to draw attention to the intentional 'blunting' of the tips of these axles. This defines the 'bearing' area on the axle slightly differently: it is now where the curved radius of the blunted tip intersects the 50-degree cone machined or formed in the axle end.
In my opinion, it follows that this very small region is the 'only' part of the axle that needs to be carefully trued and polished. But there is another implication of this radius: it maintains a good contact area on both ends when the two sideframes equalize...
Naturally there is a small deformation between the near-point contact of the relatively hard axle and the softer sideframe material -- the latter will, ideally elastically, deform slightly to give the required bearing area. I suspect you'd need very good instrumentation to measure this.
A Delrin sideframe will distort 'more' than a brass one, but the inherent low surface activity of acetal will ensure low friction of the 'deformed' area even without lubrication.
Something I have not read about is the bearing arrangement used for those trucks with rotating simulated roller-bearing endcaps. Those usually involve a small 'wire' extension on the axle end that penetrates the sideframe. Now if you remember your Hot Wheels cars, those use a Delrin tube bearing with line contact to a thin wire axle... and roll very well. The question is whether the rotating-bearing trucks 'bear' on those pins, or on a contact with the axle taper inboard of the pin end.
Sheldon, thanks for your informative post.
I find your first diagram interesting regarding axle length. When I decided to go with metal wheelsets, I measured the original axle and also the Intermountain and Proto metal wheelsets I had acquired. I had noticed that another vendor offered a variety of axle lengths and a chart to chose the best length item for a particular freight car, which made me wonder how important axle length is.
I found that the Intermountain wheelsets did very well in downhill rolling resistance as long as the IM axle length was not much longer (it was often shorter) than the original. So that became my default. I used the Proto in cases where I wanted the ribbed back wheelsets for older cars.
Your explanation firms up my guess that shorter axle lengths than original are usually not an issue because the axle point does not need to ride in the very end of the cone. Of course, too long an axle length, exerting horizontal force into the cone ends would not be desired, as that would creating a binding force.
Paul
Modeling HO with a transition era UP bent
Thank you for the great analysis. Are there any studies or opinions as to the use of lubricants on the axel tips as to rolling qualities or incompatabilities of materials? These lubricants would include everything from the Kadee "Grease-Em" to the line of Labelle products and anything else (i.e powdered graphite or Teflon type product) being marketed. I model On30 using the stock Bachmann trucks and have never lubed or adjusted any of their trucks as they seem to roll just fine. Any opinions on the "truck tuner"? Or "truck tuner" and a lubricant? Just something I've kind of wondered about but never tried.
Again, thanks to Sheldon for the great information.
Mark B.
Truck tuning often makes good sense. Note that it works by smoothing the 60-degree cone in the sideframe. Even though the 'active' bearing area might be only from about 5 degrees before and behind 'top center' and only a few thou long, it's easiest to cut and smooth the whole cone at one time.
The lubricated area on these is small and any hydrodynamic bearing wedge likely slight at most. I think the use of lube depends on the sideframe and axle materials -- and only the smallest amount. Dust will preferentially get up in there over time if you overlubricate, and it can be surprising how little constitutes 'over'doing it.
riogrande5761 Good info for novices!
Well, this novice sure learned something.
Thanks for your work in putting this together Sheldon, I found it very informative.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
I appreciate all you went through to provide us with your informative post, Sheldon. It's good, solid, information, well thought out, and well-presented. Thank-you.
It is not that things don't mater (spung trucks, etc.), it is just that if enough other things happen (bolster rub or missing exact center at attachment point, etc,), then it negates the effectiveness of the item. The reason for extra weight on sprung trucks is it counteracts the dozens of things that negates their effectivness (in other woods, all things do not scale due to gravity etc.).
Mark B Thank you for the great analysis. Are there any studies or opinions as to the use of lubricants on the axel tips as to rolling qualities or incompatabilities of materials? These lubricants would include everything from the Kadee "Grease-Em" to the line of Labelle products and anything else (i.e powdered graphite or Teflon type product) being marketed. I model On30 using the stock Bachmann trucks and have never lubed or adjusted any of their trucks as they seem to roll just fine. Any opinions on the "truck tuner"? Or "truck tuner" and a lubricant? Just something I've kind of wondered about but never tried. Again, thanks to Sheldon for the great information. Mark B.
As Overmod points out, the truck turner is useful to insure a smooth bearing surface in the journal.
I use Labelle 108, I prefer it over graphite or Teflon powder.
Another guy I ran into years ago who also puts Intermountain wheels in Kadee trucks, uses 108 as well.
One other note about Overmods earlier comments, yes, no matter how sharp it feels to you, the axle tip is rounded off, to the benefit of the actual contact point.
Your presentation of that information was very well-done, Sheldon. I am not at all surprised.
Wayne
I have been replacing the Kadee sprung trucks on cars with Tahoe rigid trucks with Intermountain wheels because I have way more problems with Kadee trucks derailing than I do with the Tahoe trucks.
Not sure whether its the springing, the Kadee journals, or that the Kadee's have code 110 wheels and the Intermountains are code 88 wheels. Just know that if a cars chronically derails, changing the trucks will fix it.
Dave H. Painted side goes up. My website : wnbranch.com
Thanks to everyone for the kind words. Having started in this hobby at age 10, with a strong boost from my father, I have been a life long student of both our models and the prototype.
I am happy to share what I have learned.
I do plan to add some additional info here, and offer some thoughts on specific things like passenger car trucks, three axle trucks, and discuss in more detail the strengths and weaknesses of rigid frame trucks and why sprung or equalized trucks are not always practical.
I wil drop this hint about that topic, cost, complexity and availablity, combined with some different physics, put passenger trucks in a different class from the general freight car fleet.
More later,
dehusman I have been replacing the Kadee sprung trucks on cars with Tahoe rigid trucks with Intermountain wheels because I have way more problems with Kadee trucks derailing than I do with the Tahoe trucks. Not sure whether its the springing, the Kadee journals, or that the Kadee's have code 110 wheels and the Intermountains are code 88 wheels. Just know that if a cars chronically derails, changing the trucks will fix it.
Are we talking about Kadee cars that came with Kadee trucks, or other cars that they were applied to?
Personally, I am not a fan of code 88 wheels, also a topic I plan to cover.
I use code 110 wheels from Intermountain, I do not use any code 88 wheels.
What kind of track? What kind of turnouts?
Logicly, and based on my 54 years at this, there is nothing inherent about sprung trucks that would increase derailments. I have nearly 800 freight cars with sprung trucks and live in a derailment free world for the most part.
I would suggest there is some "combination" of factors at work here. Some lack of compatibility in the whole "trackwork/coupler/truck" system.
I would be interested to here more details - types of cars, which sprung trucks, what kind of derailments, types of track.
Nice analysis, Sheldon.
I've used sprung trucks for decades, because despite what many folks argue, they derail much less frequently than rigid frame trucks.
One thing that you didn't mention is that rigid frame trucks may be slightly warped because of internal stresses in the frames, aggravating the floating wheel problem.
Mark P.
Website: http://www.thecbandqinwyoming.comVideos: https://www.youtube.com/user/mabrunton
Hi Sheldon,
I want to ask you whether or not you feel it is worth the expense to switch all of my 230+ cars with rigid trucks to sprung trucks given the following:
- Very few of my trains will be longer than 8 - 10 cars (Okay, I'll probably run longer trains sometimes just for fun),
- There are no grades and I'm not going to indulge in superelevation,
- I already have Intermountain wheel sets in almost all of my rolling stock,
- All of my freight cars/passenger cars are weighted to NMRA recommendations,
- All of my couplers are either Kadee #5s or #48s,
- I do not anticipate operating at breakneck speeds.
Switching to sprung trucks will cost a fortune! Is it worth the expense?
Thanks,
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Some related topics:
Passenger trucks - sprung and equalized passenger trucks are available, and are nothing new.
Central Valley and others offered the most popular styles going back to the late 50's and 60's.
Today Precision Scale Company makes a wide selection of both kits and RTR sprung passenger trucks - but get your wallet out - with many prices in the $35 to $50 a pair range.
And honestly, because of their complexity and often brass construction, they can be fussy and short circuit prone if not perfectly assembled.
While I still consider equalization important, I have found a few things to be true about passenger trucks that make rigid trucks more forgiving than their freight counterparts.
Facts to consider:
Even long passenger trains have much fewer cars - 15 or 20 passenger cars is a long train, compared to my 40 plus car freight trains. I think for a great many of us, 8-12 cars is a more typical passenger train. Mine seem to mostly vary between 10 to 15 cars.
Passenger trucks are longer, which, if made out of plastic, makes even rigid trucks more flexible. Example - if you set a chair on an uneven floor it wobbles, but a table on a similar floor will likely flex and sit fine.
Passenger cars are, or should be, heavier. But yet still often ride on four axles, changing the dynamics of their tracking somewhat and possibly taking advantage of the flexibility of a plastic rigid truck.
Don't get me wrong, in a perfect world I would prefer equalized trucks on all equipment, but cost, reliablitly, availablity and need are factors to consider.
It would be a happy day if Kadee or someone developed a magic bullet in the form of a simple, affordable, equalized passenger truck, but given the limitations I don't see that happening.
My own passenger fleet rides on a lot of different trucks, only some are sprung and equalized. Many are Athearn and ConCor 72' cars, and ride on the original plastic rigid trucks refitted with metal wheels if they did not come that way.
Others ride on vintage Central Valley sprung metal trucks, brass sprung trucks or various original equipment trucks.
Three axle trucks - rigid or sprung require additional side play in the center axle, and require extra vertical play on rigid sideframe trucks. The goal being to have the car weight on the outter two axles and have the center axle go along for the ride on three axle rigid trucks.
As I add these additional topics, I will limit the scope of each post to make specific responses simpler to qoute.
hon30critter Hi Sheldon, I want to ask you whether or not you feel it is worth the expense to switch all of my 230+ cars with rigid trucks to sprung trucks given the following: - Very few of my trains will be longer than 8 - 10 cars (Okay, I'll probably run longer trains sometimes just for fun), - There are no grades and I'm not going to indulge in superelevation, - I already have Intermountain wheel sets in almost all of my rolling stock, - All of my freight cars/passenger cars are weighted to NMRA recommendations, - All of my couplers are either Kadee #5s or #48s, - I do not anticipate operating at breakneck speeds. Switching to sprung trucks will cost a fortune! Is it worth the expense? Thanks, Dave
In your case, no, very little would be gained.
The payoff to sprung/equalized trucks is long heavy trains, particularly thru complex trackage. As the total train weight increases, the side load on wheels and flanges increases on curves for the cars at the front/middle of the train.
With equalized trucks these additional forces are much more evenly distributed to each wheelset.
Remember what Kevin posted above about the Scale Rails club? Sprung trucks required - they pull long trains.
But, given a choice for a replacement or on a scratch built car, I would pick Kadee or some other high quality sprung truck even if my other rolling stock was not so equiped.
ATLANTIC CENTRALIn your case, no, very little would be gained.
Thanks for your advice.
I will keep your recommendations in mind if I have any cars that consistently derail after all the basic tuning efforts have failed. Adding sprung trucks in that case would seem to be a logical move.
I will also say thanks for your analysis of truck dynamics. You put a lot of time and effort into providing us all with valuable information.
Cheers!!
ATLANTIC CENTRALIt would be a happy day if Kadee or someone developed a magic bullet in the form of a simple, affordable, equalized passenger truck, but given the limitations I don't see that happening.
Yeah, but we can dream.
Sheldon: Thanks for starting this informative discussion. Your comments are very insightful and very well written. Easy to understand.
Others who contributed: .... Thanks for your informative comments, too.
I have changed trucks on plastic passenger cars made by Rivarossi, Con Cor, and IHC. The replacement trucks have been mostly out-of-production trucks made by Central Valley, Tenshodo, and the IHC premium line.
My Walthers heavyweight cars with 6-wheel trucks were not free rolling when new. I used Labelle 134 teflon lubricant in each bearing, and that quickly solved the problem. I also use Labelle 135 graphite. I have used teflon on Walthers streamline cars with 4-wheel trucks, too, and am pleased with that.
My BLI California Zephyr cars have not had issues with lubrication. However, the corners of the truck frames did strike the inside surfaces of the body skirts on tight curves. A little filing took care of that.
Regarding Code 88 wheels on freight cars, some of them derailed if trunouts were not perfect. Therefore, I use Code 110.
I have not experienced freight car derailments because of rigid trucks, and most of mine do not have real springs.
Again, Sheldon: .... Thank you !
GARRY
HEARTLAND DIVISION, CB&Q RR
EVERYWHERE LOST; WE HUSTLE OUR CABOOSE FOR YOU
So the last several posts brought up comments about code 88 wheels, a topic I was planning to explore here anyway.
Before I get started, please understand, my thoughts on code 88 wheels are my OPINION, based on some simple facts. I am not suggesting code 88 wheels don't work, but they don't work well enough for me, on the track and turnouts I use.
What is a code 88 wheel? - it is a semi scale wheel with a overall width of .088", compared to the original NMRA standard wheel of .110". A true scale wheel would only be .064" wide in HO scale.
Just like our wheels are not exactly scale, our track is not exactly to scale either. It allows for more play, larger flangeways, etc, when compared to the prototype.
Code 88 wheels are simply the narrowest wheel that is expected to nogotiate NMRA standard HO track without derailment. This does however cause issues with wheels possibly droping into, or "bumping over", turnout frogs much more so than the wider code 110 wheel.
When you replace the code 110 wheels in a model trucks with code 88 wheels, you move the outer face of the wheel father from the back of the sideframe. This is not prototypical, the wheels faces on the prototype are pretty close to the back of the sideframe.
So code 88 wheels offer a finer, more scale appearance to the wheel, at the expense of the overall visual proportions of the truck as a whole which was designed for a reasonable prototype proportion with code 110 wheels, despite being slightly wider than prototype trucks.
I am unaware of any trucks on the market that use code 88 wheels and bring the sideframes in to a more scale width. A tooling expense no one seems willing to do at this point.
You are in fact improving one out of scale appearance without fixing the related out of scale distance between the sideframes, and thereby drawing more attention to that fact.
And the wheels are still wider than scale?
Rigid trucks or sprung, code 88 wheels will "clunk" thru many of the commercial turnouts on the market.
I use primarily Atlas Code 83 Custom Line turnouts. The operation of code 88 wheels thru that product is at best "clunky".
This video should give you some idea of why a more narrow wheel can cause issues at turnout frogs. They address that issue in the video.
https://www.youtube.com/watch?v=MbSmoUH1Cqk
So I ask why use them? I have decided not to on my equipment.
But my disclaimer is this, I'm a bigger picture modeler, building a larger layout, viewed from a generally greater distance, with a large fleet of cars expected to run reliably on several thousand feet of track - that is for me more important than very small gains in scale appearance.