What’s the REAL minimum radius of locomotives and rolling stock?

[gdelmoro]

Ever purchase a locomotive or 85’ passenger car advertised by the manufacturer to run on 18” curves only to find it regularly derails on 20, 24 or even 26” curves? 

It’s happened to me. So the question is what’s a produt’s real minimum radius? How do manufacturers come up with the number?

[RR_Mel]

When I was working in communications and electronics I figured specs were placed on a dart board and the one in charge was blind folded and tossed darts for each product.

 

 

 

 

Mel

 

Modeling the early to mid 1950s SP in HO scale since 1951

 

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

 

I'm beginning to realize that aging is not for wimps.

 

[gdelmoro]

LOL I think you may be right Mel! 

Clearly there is a problem but whats a good rule to follow? If they say 18 make it 28? If they say 22 make it 32?

[ATLANTIC CENTRAL]

gdelmoro

Ever purchase a locomotive or 85’ passenger car advertised by the manufacturer to run on 18” curves only to find it regularly derails on 20, 24 or even 26” curves? 

It’s happened to me. So the question is what’s a produt’s real minimum radius? How do manufacturers come up with the number?

 

Here is a good rule of thumb for rolling stock,

3 times the truck centers = minimum radius

85' long pasenger car, about 10" truck centers, 30" radius.

40' box car, 5" truck centers, 15" radius.

 

For steam locos,

10-12 times the rigid driver wheel base.

Typical 2-8-2, 2.25" wheelbase, 22" radius.

your mileage may vary....

Sheldon

[Bubbytrains]

gdelmoro

Ever purchase a locomotive or 85’ passenger car advertised by the manufacturer to run on 18” curves only to find it regularly derails on 20, 24 or even 26” curves? 

It’s happened to me. So the question is what’s a produt’s real minimum radius? How do manufacturers come up with the number?

 

Advertised to operate on 18" has implied conditions with it, namely ideal track, "reasonable" operating speed, and the rolling stock is in proper operating condition. 

In your specific case, have you made absolutely certain that it's not YOUR fault? Is your trackwork up to snuff? Your mention of derailing on your 24" or 26" curves makes me question your trackwork. Not to imply you have totally crappy trackwork, but it might be something very tiny and not obvious. Even a speck of ballast. My skepticism is not without merit because just this week we had some fellow on this forum who had a similar situation, and turns out it was his fault. 

Second, did you make sure the car's wheels are in gauge, AND, if in gauge, are not shifted on the axle a different amount? Make sure the truck screws are adjusted proper tension. The manufacturers test their m.o.r. using ideal samples, but we all know that production items are often less-than-perfect out of the box. Unfortunate, but true. Often (usually?) need tweaks.

Third, what speed are you operating? Model Passenger trains can't really handle higher end prototype operating speeds, especially at curves. 

Only then, after these more expected problems are ruled out should we begin to question if an item is incorrectly designed. This is NOT intended to give model train manufacturers a pass, but I've seen a lot of knee-jerk reactions from model railroaders to know we are quick to blame others before looking at our own faults. Especially when it comes to trackwork. I'm NOT accusing, just skeptical.

 

 

 

[gdelmoro]

Thanks Sheldon, now why isn’t that in the “How to be a Model Railroader” book? 

[ATLANTIC CENTRAL]

gdelmoro

Thanks Sheldon, now why isn’t that in the “How to be a Model Railroader” book? 

 

Expressed somewhat differently, similar recommendations are in the NMRA publications....have been for 50 years or more....

Sheldon

 

[Bubbytrains]

Here's the specific "humble pie" incident I refer to:

"Here I go again. Looking for help when I can’t figure it out.  All my locos steem and diesel, 2-8-2’s, 4-6-2’s, 4 axle, 6 axle and 80’ passenger cars run smoth through this 26” curve but a 4 axle RDC gets to one point of the curve and it slows - sounds like grinding and then proceeds through, If I run oit at a slow speed to gets stuck.  I can move it with my hand through the curve and don’t feel any resistance.

Ideas??"

 

LATER:

"SOLVED !!!!

There was a track nail sitting a little too high (not snug to the tie). I crawled under the layout, Removed a cross member of the benchwork (temporary) and created a access point. Not easy for an old man. Then I slowly ran the loco until it stopped. With my hand I moved the loco and could hear something grinding. Nothing visible arround the loco but underneath I found this nail.  

It was painted so I never would have seen it unless I was right on top of the track. Lifting up the loco i could see slight scratches on one of the underside details.

I don’t understand why the loco caught this nail in only one direction but now it works.

Next step is to re-install the scenery partition and finish the tunnel portal.

Thanks for all the replies.

PS  I HATE when Rich says it’s trackwork because he’s been right so far 100% of the time."

 

Fact is, we all have to swallow our pride sooner or later. Model Railroading is great for revealing our faults.

 

[riogrande5761]

So getting back to the OP's dilmemma, why don't locomotives and passenger cars operate on the advertised minimum radius?

Shouldn't they?

Aside from that, many people, like with computers, expect things to work well at minimum specs, which never seems like a good idea, trains or computers.

[selector]

Yes, they darned well should.  But..................................nothing we handle in the hobby, except for tracks and ground foam, and I guess adhesives, are mass produced.  They are hand assembled, meaning the variance is quite high in fit and finish.  I purchased that four-pack Spectrum heavyweight passenger car in Pennsy livery that some of you know...maybe too well.  I had to order the under/over shank Kadee couplers so that they would couple to each other.  Four cars, same supplier, same importer, same style, and no three of them would shake hands. And these were Spectrum!

Walthers used to advertise that their heavies were suitable on 24" curves. Nyuh-uuuhh!  Not even close.  I was pretty good at laying 24" curves on my second layout when I purchased them.  I found out the hard way that backing those cars through pristine 24" curves was a pipe dream.

Then some of you may recall my foray into curved #7.5 Code 93 Walthers/Shinohara turnouts on that same construction.  What a nightmare.

Soooo...yes, I think they should all be more careful about their specs.  However, there is so much human activity in our hobby on both sides of the ocean, shipper and user, that it's a lot of trail and error at times.  We know my curves weren't really 'pristine'...at all.  They were close, but they weren't consistent through their arc.  It wasn't until I got them out to 27+" that I had consistently reliable rolling characteristics in both directions.  Was it me?  The way the diaphragms worked?  The way they were attached to each rolling item?  It was all of it.

[ROBERT PETRICK]

I put all of this into the same category as the dealer response to those EPA stickers on new cars: Your Mileage May Vary.

Robert

[ATLANTIC CENTRAL]

OK, if you really want to understand what goes on when your train goes around a curve, here is some light reading:

http://webspace.webring.com/people/ib/budb3/arts/tech/curv.html

The website this info comes from is full of detailed technical info about model trains:

http://webspace.webring.com/people/ib/budb3/index.html

Sheldon

[ATLANTIC CENTRAL]

selector

Yes, they darned well should.  But..................................nothing we handle in the hobby, except for tracks and ground foam, and I guess adhesives, are mass produced.  They are hand assembled, meaning the variance is quite high in fit and finish.  I purchased that four-pack Spectrum heavyweight passenger car in Pennsy livery that some of you know...maybe too well.  I had to order the under/over shank Kadee couplers so that they would couple to each other.  Four cars, same supplier, same importer, same style, and no three of them would shake hands. And these were Spectrum!

Walthers used to advertise that their heavies were suitable on 24" curves. Nyuh-uuuhh!  Not even close.  I was pretty good at laying 24" curves on my second layout when I purchased them.  I found out the hard way that backing those cars through pristine 24" curves was a pipe dream.

Then some of you may recall my foray into curved #7.5 Code 93 Walthers/Shinohara turnouts on that same construction.  What a nightmare.

Soooo...yes, I think they should all be more careful about their specs.  However, there is so much human activity in our hobby on both sides of the ocean, shipper and user, that it's a lot of trail and error at times.  We know my curves weren't really 'pristine'...at all.  They were close, but they weren't consistent through their arc.  It wasn't until I got them out to 27+" that I had consistently reliable rolling characteristics in both directions.  Was it me?  The way the diaphragms worked?  The way they were attached to each rolling item?  It was all of it.

 

Selector,

Those Bachmann heavyweights, from nearly 20 years ago, did not have the best coupler mounting system.

But just like this thread, they refected the endless desire to make scale models go around toy train curves.

I have those cars, they run great - around my 36" radius curves now that they have true body mounted couplers and American Limited diaphragms.

I don't want to sound like a "radius snob", but I have never understood why people even want to run 85' passengers cars around 24" radius curves - they look like HO versions of LIONEL.......

I have 36" and larger curves, and even with that, I use mostly "shorty" 72' passenger cars.

BUT, my "selectively compressed" passenger cars are close coupled with working/touching diaphrams.

And they look realisticly graceful on my 36" and larger curves.

I really should take a photo of some of my whole passenger trains, sitting on a curve....

Sheldon

[Drumguy]

I think the biggest factor in the minimum radius game is speed. The manufacturers are trying to market to the largest possible base. Therefore, “minimum radius” is a more desirable advertising metric than “desirable radius.” More folks have minimum 22’s Than 32’s +, so they tell us it will work on a 22. It’s not deceptive advertising, it’s just marketing. It will work on a 22—at 10% throttle. For mainline passenger speed, it will need something significantly wider.

My minimum radius is 26, most are 30, but I like those big articulated steamers, so I’m willing to slow them down to navigate that 26” curve.

[dknelson]

Read literally, if a manufacturer claims a passenger car will run on 18" radius curves that means, as I read it, only that if you put the car on a curve of that radius you can push it around the curve and it won't derail.  Will two such cars coupled together still run on that 18" radius curve?  They don't claim any such thing when they boast of an 18" minimum radius.

In practical operation, what is it coupled to?  Many locomotives, particularly with body mounted couplers, have a coupler swing that effectively increases the minimum radius of whatever it is they are coupled to, sometimes considerably.  So what you really need to know is, what is the effective and practical minimum radius of the locomotive and car(s) you intend to run?   And not shockingly, no manufacturer can presume to guess what that is.

In short, 18" radius for the car alone, perhaps .... but so what?  It is going to be coupled to something.  And that changes everything.

Dave Nelson

[Bubbytrains]

riogrande5761

So getting back to the OP's dilmemma, why don't locomotives and passenger cars operate on the advertised minimum radius?

Shouldn't they? 

Like I thought I implied, they mostly do. As long as they're given a chance to, with decent track, in proper condition, and at reasonable speeds. 

[Bubbytrains]

dknelson

Read literally, if a manufacturer claims a passenger car will run on 18" radius curves that means, as I read it, only that if you put the car on a curve of that radius you can push it around the curve and it won't derail.  Will two such cars coupled together still run on that 18" radius curve?  They don't claim any such thing when they boast of an 18" minimum radius.

In practical operation, what is it coupled to?  Many locomotives, particularly with body mounted couplers, have a coupler swing that effectively increases the minimum radius of whatever it is they are coupled to, sometimes considerably.  So what you really need to know is, what is the effective and practical minimum radius of the locomotive and car(s) you intend to run?   And not shockingly, no manufacturer can presume to guess that that is.

In short, 18" radius for the car alone, perhaps .... but so what?  It is going to be coupled to something.  And that changes everything.

Dave Nelson

 

Well stated, Dave. There is no "official" definition of what the claim means, so it's indeed open to interpretation. I tend to read such claims with a grain of salt, as I do ANY claim that ANY business makes these days. Often a matter of Ideal conditions versus reality. You know any manufacturer will stretch a product claim as far as they can legally go, and then often push the boundaries beyond legal. Prime example these days is the term "natural" food, which people assume means something but it doesn't. As Dave says, a car said to "operate on 18" curves", has no strict agreed-upon conditions, nor guarantees about how well it will operate or how good (or terrible) it will look. I tend to think of the 18" claim in minimalist terms, that I could put the single car alone on the track and push it by hand, slowly. Beyond that, though, you're on your own if you try to couple it to another car and power it with a locomotive. 

I do have a lot of experience in this matter, as most of my layouts in my 40+ years in the hobby have made liberal use of 18" curves. There's a lot of rolling stock I've bought that has been forced into being hanger queens because of this issue. A lot of times it's a particular combination that won't work, but separately, or in the same train but not coupled together they might be fine. Any time you operate near tolerance limits of equipment it's a crap shoot. I think some of the most successful model railroaders are those who like to tinker with things (and have the budget and time).

[MisterBeasley]

I bought a set of Rivarossi coaches advertised to run on 18 inch curves.  They did.  But I quickly found out they would not run on 17 15/16 curves.  I relaid one arc of track to bring it up to 18 and they worked fine.

 

[selector]

Well, fellas, why bother putting a coupler on two ends of a passenger car rated for 24" radius if you can't expect to run them....ummmm.....you know.......

Sheldon, I like the cars and have enjoyed them.  Dispite my dismay at my initial impression of them once I tried to trail all four behind my K4, I thought enough of them to order the fix-me couplers and get them to work.  In fact, I have never encountered another problem since replacing two of those couplers, the ones that sagged the worst.  

As for the Walthers cars, I based my yard curves on their stated 'facts'.  Silly me.  Just like I was silly to swallow their claims for their curved #7.5 unchewed.  In any case, it was just shoving them in the yard throat where I sometimes had a derailment...sometimes as in about 70% of the time.  Out on the mains, my minimum curves were 28" with the outside main being 46".

-Crandell

[gdelmoro]

Bubbytrains, That guy may very well have been me! I had an RDC stalling at a certain point on a curve. Turned out to be a nail.

I never run my trains more than 40 SMPH, most run slower.

The cars that derailed for ME were a tandem BLI coach and a 6 axle diesel.

I have to say that you are correct! 90% of the time it’s trackwork.

The reason for the post is I have seen others have the same problem and I thought I would put the question out there. So far, there have some very useful replies.

[rrinker]

 The ones that say 18" radius - will run on 18" radius, as long as they run alone, or have the diaphragms removed, and, in some cases, have the long shank couplers in place. Some come with 2 sets of couplers, the shorter ones for large radius and the longer ones to get around the shorter radius. Or they have some sort of mechanism geared with the trucks to swivel the couplers.

 Even then they will never go through at speed. Besides, other than for marketing reasons, I don't know why you would want to. An 85' car looks absilutely ridiculous on 18" radius curves, not to mentions will sideswipe most lineside detail. But, if you get a bunch of 18" radius pieces of sectional track and lay it on a plain sheet of plywood, if they say the car will handle 18" radius, it will.

On my old layout, it's a good thing I tested first. Walthers 85 foot cars would not pass one another when the inner radius was 30" and the outher was 32". I had to open the spacing on the curves to allow them to work. If there are problems at 30 and 32, expecting them to work on 18 is IMO unreasonable.

There's a reason all the old stuff was made short and not to full scale. It wasn;t becauyse the manufacturers wanted to make poor models, they wanted to make models that would run on the very prevelent 18" (and sometimes 15") radius curves people were building HO layouts to back in the day.

                                      --Randy

 

[gdelmoro]

ATLANTIC CENTRAL

OK, if you really want to understand what goes on when your train goes around a curve, here is some light reading:

http://webspace.webring.com/people/ib/budb3/arts/tech/curv.html

The website this info comes from is full of detailed technical info about model trains:

http://webspace.webring.com/people/ib/budb3/index.html

Sheldon

 

WOW - Thanks Sheldon - Great sites!

[gdelmoro]

Drumguy

I think the biggest factor in the minimum radius game is speed. The manufacturers are trying to market to the largest possible base. Therefore, “minimum radius” is a more desirable advertising metric than “desirable radius.” More folks have minimum 22’s Than 32’s +, so they tell us it will work on a 22. It’s not deceptive advertising, it’s just marketing. It will work on a 22—at 10% throttle. For mainline passenger speed, it will need something significantly wider.

My minimum radius is 26, most are 30, but I like those big articulated steamers, so I’m willing to slow them down to navigate that 26” curve.

 

That’s interesting Drumguy, Are you talking about decopods? Or Big Boy locos.  I have never tried them because i thought it just wouldn’t work.  I have a 1990’s riverarossi 4-6-6-4 I’m thinking of converting to DCC but I really would like to find some way to test run it first.

[gdelmoro]

So I’m glad I asked the question. As always I lean something from forum members. Here I leaned about calculating minimum radius based on truck spacing and that the couplers as well as the particular string of cars influences minimum radius. Also got a new website.

Finally, as I have learned the hard way “Assume it’s trackwork until proven otherwise” 

[BRAKIE]

ATLANTIC CENTRAL

OK, if you really want to understand what goes on when your train goes around a curve, here is some light reading:

http://webspace.webring.com/people/ib/budb3/arts/tech/curv.html

The website this info comes from is full of detailed technical info about model trains:

http://webspace.webring.com/people/ib/budb3/index.html

Sheldon

 

Sheldon,I know none  of that gibbly gook babble and been backing long cars through #4 switches with those so called terrible "S" curves and around curves.

Its all in the wrist. Control that and one will be surprise how forgiving our models are.

[ATLANTIC CENTRAL]

BRAKIE

 

 

ATLANTIC CENTRAL

OK, if you really want to understand what goes on when your train goes around a curve, here is some light reading:

http://webspace.webring.com/people/ib/budb3/arts/tech/curv.html

The website this info comes from is full of detailed technical info about model trains:

http://webspace.webring.com/people/ib/budb3/index.html

Sheldon

 

 

 

 

Sheldon,I know none  of that gibbly gook babble and been backing long cars through #4 switches with those so called terrible "S" curves and around curves.

Its all in the wrist. Control that and one will be surprise how forgiving our models are.

 

Yes Larry, I understand.

But are your long cars close coupled at scale distances with body mounted couplers and working diaphragms?

Sure with talgo couplers, and enough spacing and truck swivel, almost anything is possible.

If I wanted that look I eould just buy and run LIONEL.........

That gibbly gook is called physics, math and engineering. Without it, trains real or model would not work.........

Sheldon

[BRAKIE]

ATLANTIC CENTRAL

But are your long cars close coupled at scale distances eith body mounted couplers and working diaphragms?

Yes..I had to back complete passenger trains around a rather tight wye (21" curves IIRC) in order to turn them.Again it was all in the wrist.

I trust you know 90% of switching problems is in the wrist?

I never had to worry about that gibbly gook babble since I found solid track work with wheels and couplers in gauge will give you endless hours of derailent free operation.

[Lone Wolf and Santa Fe]

All I know is that if the box says it requires 22 inch radius or larger that it won't run on 18 inch curves.

[BRAKIE]

Lone Wolf and Santa Fe

All I know is that if the box says it requires 22 inch radius or larger that it won't run on 18 inch curves.

 

 

Great answer that completely sums it up...

Those passenger  cars I shoved around the wye was up to par with correct wheel gauge and coupler height.. The engine I used was my favorite Atlas/Roco S4 that would crawl from tie to tie. A steady hand on the throttle was required to maintain a slow steady speed.

If that was a DCC layout I would have used speed step two or three. I understand today the club is DCC and has rebuilt the wye with larger curves.

 

[wjstix]

Sometimes you have to read the fine print...I've seen ones where the manufacturer will say something like 'can be adapted to take 18" radius curves, 24" curves recommended". So you might have to trim back the centersill on a passenger car a bit for example, if you want to use it on the sharper curves.

BTW, a good test is to get some say Atlas or Bachmann 18" radius "click track" and run the cars or engines through there. If it works on the "click track" but not on the layout, you might have a kink in the track or something - just enough to make things not take the curve.