Minimum Radius - Get yer Soapbox Out

Discussion in 'Track Planning' started by kchronister, Sep 7, 2005.

  1. kchronister

    kchronister Member

    Okay, for the first time (fourth layout), I'm actually building completely from scratch. Unfinished basement and no "legacy" benchwork, rooms, walls, etc. I have approx 14x20 with a 7x9 alcove area (see good news, bad news thread for that).

    So... I've been 'round the block a few times, and I certainly know that "wider is better". I've experienced that myself. But how much is too much. I just finished some layout roughs using 32" mainline radius (when I say min. I mean mainline), and what seemed like (is) about twice the space I've ever had sure got eaten up fast.

    I think back to days of 22" minimums and that 'squished' down to maybe 21 in a few spots if I'm honest... Oh how I longed for solid 24" radii. Now that I could easily do 24's... Here I am yearning for 30" plus.

    So how much is too much? All but the most monster of articulated engines will take 24's... And I model 1940's PRR, so I'd really have to push the limites of prototype to run articulated anyway. I have long, long passenger cars (i.e. prototype length), but they did fine on my 21/22, so clearly 24 will work...

    So at 30"+... Are we just talking aesthetics? Is there any real functional reason for more than 24" with my era, rolling stock and so forth?

    I've never known the community to be shy, so have it it. Stand on your soapbox and explain to me EXACTLY why 30" is bare minimum, why anything over 24" is a waste, etc. etc... Let's hear it. I know what I think, I don't need YMMV or IMHO. Let's hear your uncensored, unvarnished opinion loud and clear. September's here and I'm a-start building in a couple months, so tell me know before I set screw to wood...

  2. Pitchwife

    Pitchwife Dreamer

    I've gone on the assumption that bigger is indeed better, as long as you can reach all of it. :thumb:
  3. Russ Bellinis

    Russ Bellinis Active Member

    I think whatever looks good to you, and is operational with your biggest locos and rolling stock is about right. If your passenger equipment works on 24 inch radius and looks ok to you, there is no reason to go with a bigger radius. The Pennsy may not have had a lot of articulated locos, but how about the Q-1, T-1, or S-1 (I may have these designations wrong, since I'm not a Pennsy modeler.) Pennsy had some truly monsterous solid frame locos. Do you run any of those or do you plan to run some in the future?
  4. Triplex

    Triplex Active Member

    33" will handle 2-10-4s and T1 4-4-4-4s; 36" should take Q2 4-4-6-4s. I wouldn't suggest going to 48"; it would look good if you were just going around the walls, but you should be thinking about a peninsula. With a four-track main and 48" on the inner track, that peninsula would have to be at least 112" wide near the end. Also, if you want to fit a turnback curve in the alcove, you can't go that large, with only 7' of width to work with. If the main were four tracks there, the inner track would have to be ~34" radius or less. I guess if you ever happened to have a Q2, you could route it to the outer track there... Whatever you do, you won't be able to get your mainline equipment into that 48" wide space under the stairs, but it should be usable for secondary or branch trackage.
  5. shaygetz

    shaygetz Active Member

    I'm reminded of a beautiful layout built in N scale, inside of a baby food jar. The guy used a silver dollar as the inside rail, then ran a second rail outside of that, then ballasted and scenicked it. A Bachmann Docksider was the only rolling stock. How tight didja wanna go? :thumb:
  6. sds888

    sds888 Member

    ok I have a question about this I am planning on building a layout and was thinking about 18" curves for HO. I was thinking a logging line on this track probably early 1900's is this going to be to tight? thanks
  7. Triplex

    Triplex Active Member

    A logging line - no, 18" should be fine. I'm assuming Shays, Heislers and Climaxes will be the motive power, or maybe small 2-8-0s. A few years later, though, and 2-6-6-2 Mallets might need 22". No curve or grade your models will take can be an exaggeration of the real thing.
  8. Ralph

    Ralph's for fun!

    I'm thinking about how great those Pennsey passenger cars will look going around 32 inch curves....... :)
  9. farmer ron

    farmer ron Member

    All I have room for is 18" inch curves for what I want to build in the space that I am building my logging rr, things work fine on it and I think it looks good, of course I would like to have 24" plus curves but I just have to work with what space I have available..Ron..
  10. 60103

    60103 Pooh Bah

    I have a theory that curves look larger seen from inside and less seen from outside. However, the whole effect is spoiled when you see 2 passenger cars spanning a quarter circle.
  11. kchronister

    kchronister Member

    Yeah, that's definitely an issue we almost can't get around as modelers. Even a 40" radius circle would give approximately 60" of track length in a quarter turn. Not two cars, but if you're talking big pullmans, it's still far too easy to have a loco through the curve on the straight and cars still _entering_ the curve behind it...
  12. spitfire

    spitfire Active Member

    Kris, what about a combination? Choose one curve for your "railfanning spot" -- one with good photo and scenic possibilities -- and give it the full treatment, 32" (or more) radius curves. Then, to fit more operation and track into the rest of the layout, use a smaller radius. You can also hide part or all of the track in some of the tighter curves.

    I'm doing my layout with one track that's for passenger (or freight) with a min. 30" radius. There's another line that's only for freight with min. 22".

  13. Russ Bellinis

    Russ Bellinis Active Member

    In our modular club, we had one member in particular who was a strict prototype modeller. He wasn't the rivet counting critical type, but he insisted that anything he built would be prototypical. He was also an S.P. modeller, and the club standards called for a double track main line. It took him quite a while to find a section of the S.P. in So Cal with a double track main, but he finally settled on San Timeteo Canyon (spelling?). He built a 6 foot module of a section of the canyon with a double track bridge going over a small creek in the middle of a large "S" curve. It was one of the best photography spots on the layout. Our minimum radius for mainlines is 36", and each module is required to have at least 4 inches of straight track at each end of the module on the mainlines. I think his "S" curve was something like 48" or 54" radius.
  14. Triplex

    Triplex Active Member

    That's assuming appearance rather than operation forces the large curves. Big steam will often have 30" or so as a bare minimum. If you don't have any, what you said is possible. The idea of cosmetic curves is common - but they're not normally used to turn corners or anything. In HO, they're usually between 96" and 200" radius, and are used more like straights in planning.
  15. VunderBob

    VunderBob Member

    A couple of thoughts. The biggest minimum radius you have room for is the best. I always think of minimums as a pair: What I'll accept for a mainline, and what I'll accept for industrial trackage.

    Currently for me, that's 24" on a main, and 18" for spurs. If I have the room, the mainline radius moves up to 30". I might go a little tighter on industrial track if I'm trying to replicate some nifty track arrangement, but 18" is about it for reliably switching 50'+ cars with Geeps.

    Similar restrictions exist for frogs. I'll never run the main through the diverging route of a commercial turnout on a frog any less than #6. #8 would be even better... I will put a #4 on the main if a spur uses the diverging route. Once off the main line, a #4 is fair game for either route within reason of space and S curves.
  16. Triplex

    Triplex Active Member

    I once heard of a modeller who would only allow #8 turnouts in the mainline even if the curved route was a branch or spur. Is running through the straight leg of a #8 smoother than doing the same on a smaller one? I would kind of think it might be the other way round, at least with insulated frogs, because the larger turnout has a longer frog.
  17. kchronister

    kchronister Member

    Okay, here's where I am on this after all the feedback (and thanks for that).

    Someone mentioned "big steam" and that's definitely a thing with me. I run several things that qualify from 4-4-4-4 T1's to 2-10-0 decapods and even one (I know, I know, not prototypical) 2-6-6-2. The mainline is double-tracked, 36" minimum radius. For primary service tracks (i.e. for passenger stations, etc.) where the big locos go, though at lower speeds I kept it to 30".

    Regarding your point, Triplex, I can't see any reason to insist on #8's for industrial sidings and the like where large stuff won't go. The vast majority of mainline turnouts WILL however be #8's (or #10's if I can find a commercial source for them...). Those will be as long as possible for several reasons - 1) Many of them are for crossovers (it's a double-track main) and will see regular use by the big iron. 2) many of them are turnouts to primary sub-tracks (station leads, etc.). But for industrial sidings, I'll use #6 to save space.

    The logging line has 18" radius, which is pretty much appropriate. Given that the motive power there is shays, heislers and climaxes, shouldn't be an issue.
  18. Russ Bellinis

    Russ Bellinis Active Member

    Don't forget, if you have an industrial siding coming off the main, you can use something as small as a #4 if you run the mainline over the straight side of the turnout and don't switch the industry with any of the large mainline power.
  19. kchronister

    kchronister Member

    I generally don't use #4's for the "looks" factor alone. But I must say that even when I have used them and even when I used rolling stock and motive power that should be able to handle them, I just find them to be constant problem-points.
  20. Triplex

    Triplex Active Member

    Remember, the minimum radius through an NMRA-standard #4 is 15". That's why using them with steam can cause problems - they're usually used with 18" curves. The average curve through the #4 is considerably larger than 18", so diesels and trains as a whole go through them reasonably smoothly. With steamers, you have to worry about axle bind. Geared locos, without fixed multi-axle sets, can certainly handle them.

    I'm not sure if #4 turnouts and sharp curves are intrinsically less reliable than larger ones - that is, do 40' and 50' cars run as reliably on 18" as 80' cars do on 30"? Some people say yes, some say no.

    I didn't say I supported the idea of #8s for spurs! I never see it on plans, and wouldn't waste the space myself. Then again, maybe I'm too used to 50s books, which don't suggest you ever need more than 30" and #6s, and never more than 18" and #4s for industries. That's probably because steam loco models were more flexible then, and large freight cars didn't yet exist in reality.

    T1s need at least 33" according to John Armstrong. However, I1s (and other 2-10-0s)can supposedly run on 26"! I've never understood that - even allowing for their smaller drivers, why should they handle tighter curves than 4-8-4s?

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