Minimum radius

Good test Tom!   Nothing beats reality.

John Armstrong, in his landmark book "Track Planning For Realistic Operation"  defined "Conventional  Curves" as 48" radius, and "Broad Curves" 54" radius for O Scale.    He said most equipment can run on Conventional Curves if easements are incorporated,  and anything can run on Broad Curves.

Thanks for posting Tom! I just recently made the switch to 2-rail O scale (5 years in HO, 10 in 3-rail scale prior). I had set my minimum radius as 54’’ for the very reasons you stated above. I’m going to keep my mainline at 60’’ at least.

Just look at that woodwork, Tom's a woodworking machine!

A number of years ago I was fortunate enough to purchase a used Glacier Park SP 2-8-0 C8 and found it could easily handle a 36” radius S curve, totally unmodified, I needed in a hidden section of my layout on a blob.  Of course no one believed me so I posted a couple of videos.  They still didn’t believe me so I had to augment the video with further proof with photos of the 36” radius Fast Track Jig.

Here are those videos:

https://youtu.be/yDg5p9wMi8E

https://youtu.be/qaqYbnZpgJM

https://youtu.be/Olv

Peter

I am glad Tom started this discussion.  Here are observations from my own layout

36" Radius (this is my minium, a lot of these can go around narrower)

MTH 2-10-0 consolidation

Sunset GP7  (fixed pilots)

Sunset GP9 (fixed pilots)

Sunset SD9 (Fixed pilots, six axle)

MTH F7 ABBA  (Fixed pilots, Factory Spacing)

Atlas RSD7 (Fixed pilots, six axle)

Weaver RSD 12 (Fixed pilots, six axle)

Atlas RS1 (fixed pilots)

MTH Aerotrain (Fixed pilot, prototypically close coupling locos and all coaches, converted to 2 rail)

All GGD 21" passenger cars  (Factory Spacing)

MTH GG1 (converted to 2 rail)

40" Radius

MTH F7 ABBA (Prototypical close coupling)

Lionel ABBA Sharks (fixed pilots, prototypically close coupling, converted to 2 rail)

46" Radius

Sunset GG1 (widened slots in four wheel trucks)

MTH P5a and P5a Modified (Fixed pilots, converted to 2 rail)

All GGD 21" passenger cars (prototytpical close coupling, diaphragms touching)

Sunset M1b 4-8-2.

Sunset B70m baggage car

All of the above curves are hidden for asthetic reasons.   Which means equipment has to be super reliable

All of the above curves have easements

One more note: Awhile back I had a Westside J1a (2-10-4). A massive locomotive that had been reworked by Ed Rappe to go around tighter radius curves.  I set up a test track, and with easements it could easily go around 44" radius curves,  going forward and backwards. It looked a bit silly with all that overhang, but that had nothing to do with the number of rails

I think I posted this elsewhere: the old Atlas F9, the Red Caboose GP9 and any of the single motored 4 axle Weaver diesels can make it around the early Atlas 24"R track. My Varney Ten Wheeler can do a 36"R. Whether they "should" or not I'll leave up to you...😁

Mark in Oregon

Tom, I remember that test track from the Towson O National. Though the only motive power I had there was On30 !

I think John's comments are based on the older USH and MG  brass and kit bullt steamers from 50s-70s.    Some of the newer large locos like the 2-10-4 mentioned above required larger radius out of the box.    And I think the KOHS and OMI stuff generally need larger radius for models of the same locos as USH or MG.

With steam locomotives it seems to me the ones with the more complex jointed main rods are more amenable to handling tighter curves.  While the GP SP C8 has all the drivers flanged, it has 2 piece main rods with quite a bit of side to side play for the center 2 driver wheel sets. I also have a NJCB 2-4-4-2 Little River that easily handles 36” radius and an older PSC Hammond Lumber 2-6-6-2T that with some insulation work and a little filing will also.  

Peter

Hello all,..my layout was made in,1939 with 48 radius ...so far everything has run,on it ...however wider is always better,...but not an option in my case ...keeping with the historic layout ..here is a video link to see a Lobaugh UP Northern ...the biggest / longest solid,wheel base engine I have ( so far) ...it's not thrilled at 48" but seems happy just to get some exercise .

Cheers Carey

https://youtu.be/f7QQshifftk

I always note - my Daylight articulated coach has an extra 1/16" in the articulation space, and cannot operate on less than 74" radius.  Ditto with some of my Northerns and all of my 2-10-2s and 4-10-2s.  I do not carve cylinder blocks or tail beams, although my tail beams are lots narrower than prototype.

@Carey Williams posted:

Hello all,..my layout was made in,1939 with 48 radius ...so far everything has run,on it ...however wider is always better,...but not an option in my case ...keeping with the historic layout ..here is a video link to see a Lobaugh UP Northern ...the biggest / longest solid,wheel base engine I have ( so far) ...it's not thrilled at 48" but seems happy just to get some exercise .

Cheers Carey

https://youtu.be/f7QQshifftk

Your layout was built in 1939? Wow.

Although not really a fan of big UP steam (sorry!), that is one impressive engine. 👍

Mark in Oregon

For those shooting for 72-inch radius, interesting to note that both F3s and GP9s had a minimum radius of 274 feet, which is 68.5 inches in our scale. On the other hand, a Baldwin 4-8-4 needed closer to 360 foot radius, almost 90 inches for us.

I'm going through design challenges right now as I'd like to use 42" radius (O-84) curves. However, I got lucky in that several MTH scale-wheel locomotives can squeeze through 36" radius (O-72) with other locomotives and/or freight cars coupled, including:

• SD70ACe
• C44-9W
• C40-8W
• ES44AC
• AC4400-W
• UP Big Boy! Yes, it can do it, but it looks weird and is my motivation for trying to do 42" minimum radius.
• U25B (of course, it has four axles and vertical can motors)
• GP35 (of course, it's so small and has four axles)
• GP38-2

Just call me someone living in both worlds.

@Carey Williams posted:

Hello all,..my layout was made in,1939 with 48 radius ...so far everything has run,on it ...however wider is always better,...but not an option in my case ...keeping with the historic layout ..here is a video link to see a Lobaugh UP Northern ...the biggest / longest solid,wheel base engine I have ( so far) ...it's not thrilled at 48" but seems happy just to get some exercise .

Cheers Carey

https://youtu.be/f7QQshifftk

Well I think that may win an award in this group as one of the oldest operating layouts! What is its history?

2 Rail Forum

One thing that I've never heard mentioned in all the many "What Radius Will It Navigate?" topics, is what effect is "What Effect Will These Tight Curves Have On My Locomotives?"

It's a pretty safe bet that the smaller the radius number, the more wear and tear there is on locomotives and track! Might be an eye opener!

Simon

When I started my layout, my target was 072. But as things worked out I ended up with 054. Luckily in my shopping, I had only bought 4 locos with an 072 requirement and those sold quickly. IMHO, 054 (and I suspect 042) is a good, practical radius for a layout builder.

Don Merz

@Don Merz 070317 posted:

IMHO, 054 (and I suspect 042) is a good, practical radius for a layout builder.

Hmm... We'll have to agree to disagree on that point.  I have a ton of stuff that requires O72, and I'm not willing to restrict myself to O54 and certainly not O42!  My minimum when I did my current layout was O72 and larger.  I compromised in one area, a couple of industry spurs that have O54 curves, but that won't affect my running the big stuff that would never be visiting these short tracks.

Happy to have you guys here, but watch out for the forum police.  Two railers deal in radius only.  Very confusing to us when you use diameters.

Morning guys, after reading all the comments, everyone has great information to share! But one thing hasn't been said.

I have an MTH ES44AC that I love and states will work just fine on O54, so when I started my layout build I was using O54 curves. Lucky me I figured out in a short period of time that with fixed Pilots and Kadee couplers it is not so! You will get binding and the corner of the cars will hit. So as for me everything on my layout is O72 or bigger. Just my two cents.

There is no right or wrong answer to minimum radius because everyone has different physical or spousal size limitations. Although I use O-72, -63, and -54 track, I am always fascinated to see how people are inventive with the smaller 4 x 8 layouts using O-42, -31 and -27 track. There are enough train products to keep the play-value high no matter what the radii might be.

@Bruce Brown posted:

There is no right or wrong answer to minimum radius because everyone has different physical or spousal size limitations. Although I use O-72, -63, and -54 track, I am always fascinated to see how people are inventive with the smaller 4 x 8 layouts using O-42, -31 and -27 track. There are enough train products to keep the play-value high no matter what the radii might be.

Very well said Bruce!

@bob2 posted:

Happy to have you guys here, but watch out for the forum police.  Two railers deal in radius only.  Very confusing to us when you use diameters.

That's a good point. Let's not forget, for example, that "054" (diameter) is only 27" radius. That's pretty tight for a large steam engine...I would think. Apples and oranges... 🙂

Mark in Oregon

Let’s remember that anything with a 0 in front of it is diameter which in radius is half that.  Also Irish people.

Peter

FWIW, removing the flange from the center driving wheel of a Rivarossi/AHM “Casey Jones” 4-6-0 (2 rail) plus elongating the slot in the pilot truck enables the loco to run on 24” radius (vintage) Atlas sectional track. The tender drawbar needs lengthened, too. Rivarossi/AHM 4-4-0’s will also run on 24” radius with a lengthened tender drawbar. 19” radius is about as tight as I care to run 40’ O scale 2 rail cars; any tighter and the car corners begin to foul each other.

Anybody who can get a Rivarrossi anything to run reliably on any radius has my admiration.  I did get the IHB to run with a couple plastic freight cars,but twice around the loop seemed like "pushing it."

I love radius debates.

I have some old 2R set track of 30" radius and a few of my locos go around them quite happily! Have attached a couple of dodgy videos.

I don't plan to use anything much less than four and a half foot radius on my layout. I currently have temporary track on my benchwork with three and a half foot radius curves but they're juuuuuust slightly too tight for some of my bigger stuff.

Mick