Help...........Min Radius for Steam Loco

[Anonymous]

I need to know what size steam loco will run on my small ho layout. I have a number of ~18 inch radius curves. Will a 0-6-0 work??? right now I run a number of small diesel switchers that have 4 wheel trucks with no problems. Thanx, Harry........................

[secondhandmodeler]

Hi Harry, welcome to the forum!  I am new as well.  I have almost all 18 inch curves.  My 2-8-0 runs just as well as my 4 axl diesels.

[selector]

Welcome, Harry.  Eighteen inch curves are good for all switchers, and with steamers up to the 4-6-4 and 2-8-2 range.  Probably most Mountain class 4-8-2 would be okay, as well.  Even a small Decapod (Russian) 2-10-0 should be okay.  The thing is that when you start pushing the upper limits on locos around your curves, your curves have to be that much more consistent, and closer to perfection.  Any dips or kinks at the joins between sections will give your locos grief.

I hope you are having fun with all these decisions!

[bighead]

hi harry and i hope you find the forums helpful! i use a 0-8-0 and it seems to work fine!

-jake =]

P.S. i once had a freind named Harry Burgure everyone made fun of him though

[MisterBeasley]

I run a P2K 0-6-0 switcher and a BLI 4-6-4 Hudson on my 18-inch curves and Atlas snap-switches just fine.  However, as I added each of these to my roster I had to make minor tweaks and fixes to remove flaws in my trackwork that never bothered my diesels.  I've also got a P1K Alco RS-3, 6 axle road switcher that is perfectly happy on my curves and turnouts.

[Darth Santa Fe]

Most steam engines are engineered to run around curves as tight as 18" (I think the Marklin/Trix Big Boy can make it around a 14" radius), but smaller steam engines work best on curves like that. You should be able to easily run anything from an 0-4-0T to a 2-6-6-2 with no trouble. Most engines with longer wheel bases (4-8-4 to 4-8-8-4) usually struggle a little around tight curves, but they'll still run. I recently got a Bachmann 2-10-0, and although it might sound big, it's actually not much bigger than a 2-6-0, and has no problem running around tight curves.

[Hoople]

I can run my Rivarossi 1960 Big Boy around 18" curves just fine. Apparently PCM/BLI's, Athearns, and Trix can do 18s. I'm not sure about the newer rivarossi.

[R. T. POTEET]

I need to know what size steam loco will run on my small ho layout. I have a number of ~18 inch radius curves. Will a 0-6-0 work??? right now I run a number of small diesel switchers that have 4 wheel trucks with no problems. Thanx, Harry........................

Harry42, your question was what size locomotive can you run on 18 inch radius curves.

I have a BALLPARK figure for computing the radius needed to operate steam locomotives.  This is strictly a BALLPARK calculation but it does correspond closely with NMRA Recommended Practices figures.  It is based upon the length of the ENGINE - by my definition a locomotive consists of an engine and tender.  A locomotive should have a radius curve equal to 37.5% of the engine length.  Manufacturers can, through the use of blind drivers and considerable lateral motion on the driving axles,  engineer their (model) engines to negotiate curves as tight as 27.5% of the engine length.

My largest HO Scale locomotive was a light USRA 4-8-2; this locomotive had a length of approximately 55 feet.  Using the above cited figures a good operating radius should be 20 5/8 inches - call it twenty and a half.  I regularly operated it on my 18 inch radius curves without problems but the appearance of the engine on this radius curve left much to be desired and it was one of the reasons I left HO Scale for N Scale.  The cited 27.5% yields a figure of 15 1/8 inches; I, of course, never tried negotiating a curve of this radius and I don't know whether Bowser designs it for operation on that radius curve but my Mountain would have looked absolutely ridiculous on that radius curve.

Big Boys have an approximate 80 foot engine length; this yields a figure of a 30 inch radius curve; most people who have owned a Big Boy will attest to the fact that 30 inches is a good radius for this size engine even if only for cosmetic reasons.  An absolute minimum radius for this engine is 22 inches - 27.5% - but it looks terrible at this radius.  The question frequently pops up "can I operate my Big Boy on 18 inch radius curves?"; probably, but I would do it in the dark myself so I didn't have to look at it.  Everybody wants to own a Big Boy!!!!

Your 0-6-0 switcher is approximately 35 feet long; 37.5% of that figure is 13 !/8 inches.  Believe it or not I have seen that tight of a curve on an HO Scale layout!!!  Don't try to do any coupling or uncoupling at that radius but the issue here is the radius an engine will negotiate.

Let's look at what size engine an 18 inch radius curve will handle.  Eighteen inches divided by 37.5% yields a figure of 48 feet and that is the engine length of a USRA Mike.  The 27.5% figure yields a figure of 66 feet, the length of Uncle John Santa Fe's 2-10-4s and that is another locomotive I would only run in the dark if I were going to run it on an 18 inch radius curve.  

[dinwitty]

All the Rivarossi engines (and equipment) could handle 18" radius. By design they made them that way. I repaired a big boy and found it could run tenderless on 15"....

Most standard models would be able to take 18" but get to higher precision models, nope.

You will be OK with a small articulated engine like a 2-6-6-2 since the articulation was meant to get a larger engine over small radius.

The really biggest beef is passenger cars on 18".  look for the shorties than full length.

Athearn purposely  shortened their RDC to handle 18", a window or 2 removed.

 all depends how you want to model. You could go 0-8-0 and be fine.

 

 

 

[wjstix]

There can be a difference between what works and what looks good. Although larger engines could take 18" curves, the largest you'd probably want to go for appearance's sake would be a 2-8-2 or 4-6-2, although a Mantua 2-6-6-2 would be OK since it's based on a logging engine designed to take sharp curves. 4-6-0's and 2-8-0's would be good choices too.

For passenger cars, only cars with truck mounted couplers will take 18" curves, regardless of length. The Athearn 70' cars will work, MDC's 60' Harriman cars might be the best choice in terms of appearance. Depends on your era, Athearn makes heavyweight and streamlined cars. 

[tomikawaTT]

  Welcome to the forums.

Assuming you are in HO, an 0-6-0 should have no problem negotiating 18 inch radius curves.  Some high-drivered six-coupled locos might.  I would caution against most 4-6-2 and 4-6-4 types, high-drivered passenger power that is much happier on conventional (24" radius) curves.

I personally own a small fleet of six-coupled locos (including a much-modified 2-6-6-2) that will handle 450mm (15"-minus) radii.  All of the 0-6-0T types ran it right out of the box.  So did my one 8-coupled tank loco, an 0-8-0T with roller skate wheels for drivers.  Note that the line was engineered that way for a prototypically valid reason - I do not recommend such tight radii as a general rule.  My mainline standard is 610mm (24 inch) radius, wider where practicable.

Chuck (modeling Central Japan in September, 1964)

[dstarr]

   Model railroad manufacturers will do nearly anything to make their product handle 18" radius curves, since so many HO railroaders have 18" curves, and the makers want to sell the product to everyone.  Anything made since the 1960's will in all likelihood go around an 18" curve and stay on the track.   The longer articulated steamers look a little foolish on 18" curves with the boiler hanging way way over the outer rail, but they don't derail. 

   Was it me, with a smaller layout and 18" curves, I'd avoid the big articulateds, and go with Pacifics (4-6-2), Consolidations (2-8-0), Ten-Wheelers (4-6-0), Moguls (2-6-0), Atlantics (2-4-2) and switchers.  If I wanted to, I could even run Hudsons, (4-6-4) and Northerns (4-8-4). 

 

 

[3railguy]

I would run nothing larger than a 2-8-0 consolidation on 18" radius. Larger locomotives do work with it but the shifting of the boiler as it enters and leaves the curves gets to a point of dorkyness taking the fun out of operation. At least in my operating fun. Body mounted couplers on larger tenders have a tendancy to pull cars off the track when running 18" radius.

[fwright]

I would run nothing larger than a 2-8-0 consolidation on 18" radius. Larger locomotives do work with it but the shifting of the boiler as it enters and leaves the curves gets to a point of dorkyness taking the fun out of operation. At least in my operating fun. Body mounted couplers on larger tenders have a tendancy to pull cars off the track when running 18" radius.

I like the 3X rule of thumb.  Three times the length of largest car/engine (I only count the engine part of the steam engine) is the minimum radius.  Is it conservative?  Yes.  But it helps prevent me from walking into wallet-depleting temptation.  I don't have to go through special gymnastics with couplers, under-body detail can be present without interfering with trucks, and I can limit lateral motion of drivers which reduces steam engine friction.

Since I have typically had small spaces and 18" minium radii in HO, I chose to model the 1900 era.  This era works well with the 3X rule with the exception of passenger cars.  With passenger cars, I limit myself to the older wood cars that were 50ft or less.

just my thoughts, yours may differ

Fred W 

[Don Gibson]

1. MEASURE THE LENGTH of you engine with a ruler.

The NMRA recommends that number (in inches) be applied to the Radius (by 3X inches) of he track. IE: 6" length X 3 = 18"radius.

X 2.5 appears to be 'accepted'. X 2 is 'pushig it'.

2. What 'will still stay on the track' is a variable - (smaller engines for tighter curves), since individual STANDARDS vary.

It's up to the individual manufacturers 'targeted' market, (and purchasers taste). (Realism, or Toy). In general: the cheaper, the tighter the curve, and vice versa.

Was it P.T.Barnum that said "No one ever went broke underestimating the intelligence of the average buyer?

(Products are 'cheapened' to sell to less 'sophisticated' buyers.(Example: 79" driving wheels reduced to 73" get around sharper curves) ... and $ell more.

[AggroJones]

Why don't you try squeezing a 4-10-10-10-6 through there.

j/k

[wjstix]

On my last layout, I had one section (leading up to an ore dock that never got built) that had 22" radius curves, and was reached thru the curved leg of a no.4 Walthers turnout. The only engine I had that didn't like it was my BLI 2-10-4, it would go thru both but there was some hesitation because it was binding a little, it's recommended for 24" radius and above.

Other engines, including E units and steam including a Spectrum 2-6-6-2, 2-10-2 and 2-10-0 were fine thru both. I suspect they would take 18" radius too, but wouldn't look too good. An 0-6-0 and 0-8-0 would be good choices, 0-8-0's usually have small drivers close together and are designed to take sharp curves in yard or industrial switching areas.

BTW an Atlantic is a 4-4-2, 2-4-2's were "Columbia's".

[TwinZephyr]

A 4-10-10-10-6... now there is something a model railroad manufacturer needs to make instead of another big boy.  Sure would be impressive to see a couple of those double heading a 12 car mixed train and switching on a branch line. 

[tomikawaTT]

Why don't you try squeezing a 4-10-10-10-6 through there.

j/k

Why not go to the absolute limit - a 2-10-10-10-10-10-4T?

A couple of generations ago, Trains had a (not so) bright ideas that were never built article about Sam Vauclain's schemes for steam-powered centipedes.  One of the illustrations was an artist's rendition of a Santa Fe ten-coupled quintuplex on Raton pass.

So, why weren't they built.  One of the last sentences in the article included, "capable of using all the steam in the boiler with a single turn of the multitude of drivers."  Makes a pretty good epitaph...

Chuck (modeling Central Japan in September, 1964)

[Don Gibson]

It was told to me by someone in the 'model train' business that 22" was the 'de facto standard'  for HO equpment. It was, of course, dictated by the widest HO curve that would fit on a 4X8 sheet of plywood'...

... and (coincidentally) where the most Dollar$ are being spent.

This is not absolute: Walthers' Budd cars designd a clever coupler pivot to drop 36"r, to 24"r. while others (Athearn, ConCor, Rivarossi, IHC,) went with Talgo mounted 'horn hooks' or (later) McHenrys.

Manufacturers aiming at the 'TOY TRAIN' market such as TYCO went with 'tighter is better'. There were others.

Now is the expected default minimum 18"? - even for a 4-8-8-4 Big boy. NOT!

ATHEARN (even with a notorious past for 'creative' dimensions) lists the "minimum radius" @ 22"r.  ThE NMRA recommends 30" + for more realistic, dependable, operation. I wonder what BOWSER's Big Boy min. is?

I THINK anyone with 18"r curves, can have a far bigger RR 'Empire' using the increasingly popular 'N' scale'. Using 'Whatever stay on the track' as a badge to brag on, is not that far from seenig how fast it will go besfore jumping the curve.

I did that when I was 5 years old.

[jjdamnit]

Hello all,

I have 15-inch radius curves on my HO pike.

The bulk of my motive power is diesel set in the late 1970's to early 1980's.

I do have two 0-6-0 locomotives for Olde Tyme excursions over the coal unloading platform and down the historic spiral trestle.

One is an oil burning Side Tank "Porter" and the other is a USRA with a Vanderbuilt tender; converted to burn oil.

Both locomotives negotiate the 15-inch curves with no problem.

The only problems I've had has been stalling of the 0-6-0 Side Tank "Porter" over the frogs. The frogs on my turnouts cannot be powered.

Because the "Porter" is used as a helper up the 3% grade to the unloading platform it does not cross over many unpowered frogs on it's own.

I installed additional pickups in the Vanderbuilt tender; linked to the decoder in the locomotive, and this unit has no problems over the unpowered frogs. 

From my limited experience with steam power on tight trackage, contrary to prototypical locomotives, leading trucks might prove more problematic; especially thought #4 or smaller turnouts. 

I'd stick to 0-#-0 steamers.

Hope this helps.