New Guy Radius Questions

Bigfoot21075 Jul 10, 2021

  1. Bigfoot21075

    Bigfoot21075 New Member

    I am trying to get back into the hobby and are starting with nothing other than cartons of 50 year old HO trains. So i am staring from zero. My space is limited, I can accommodate a 4x8 and have been using SCARM to make some rather boring layouts because I felt constrained by turn radius issues. I have read over and over that anything below an 18" radius does not look right and smaller than 15" will derail and burst into flames unless it is in the yard only, where below 11" causes death there.

    THEN I stumble across this FANTASTIC layout on You Tube. It claims to be a 4x8 but how can this be? The station tracks is the video must be separate right?

    What is the real truth here? I am shooting for a 40's era probably somewhere in Appalachia or even Ellicott City type of look (I live around there, we have the Nations oldest remaining passenger train station).
  2. Hytec

    Hytec TrainBoard Member

    Hi Bigfoot, welcome. Glad to have you aboard. Here's a brief answer to your question.

    You say you're modeling in HO-Scale. The title of the video says N-Scale. That's a big difference in size. N is about half the size of HO. For instance a realistic curve in N is a radius of 18". Minimum radius for most N locomotives is 11". and minimum radius for anything except trolleys is 8-1/2".

    You can make a nice 4'x8' layout in N-Scale as shown in the video. An HO layout is doable, but crowded.
    Martin Station likes this.
  3. Martin Station

    Martin Station TrainBoard Member

    Welcome! Years ago when I Built a HO layout on a 4x8, I found That I could use 22" radius on the outside and 18" radius on the inside and it worked ok. You are best using 40' box cars and flat cars and smaller two bay coal hoppers. If you are modeling the 1940s, this is what they mostly ran. Smaller locomotives would also run/look best. I'm not a steam guy, but I would think 0-6-0, 0-8-0, 2-8-0, 4-6-2, even a 2-8-2 would be fine. Diesels would mostly be 4 axle so you will be fine there too. Hope this helps.
    Mark Ricci likes this.
  4. sd90ns

    sd90ns TrainBoard Member

    If you want to build an N-Scale layout on a 4x8 foot tabletop, pick a nice HO plan for that size then build it in N-Scale making adjustments for track spacings and elevations.

    This will give you moderate grades and lots of space for scenery and additional spurs for industries or a couple of extra yard tracks if you so choose.
  5. Doug Gosha

    Doug Gosha TrainBoard Member

    Yeah, the layout in the video is obviously N scale.

  6. freddy_fo

    freddy_fo TrainBoard Member

    This is a 4' x 8' layout plan I made that uses a minimum radius of 15.5" on the inside track for the figure 8. All other radii are 17" except for the track from the switching yard to the roundhouse. I've tested my big boy on the 15.5 and it negotiates it just fine along with a schnabel car that is super finicky about tight turns. This illustrates if anything that 18" on a 4x8 is very doable.

    n_fleischmann-piccolo-john-4-staging yard.jpg
    Mudkip Orange, Hardcoaler, MK and 2 others like this.
  7. bill pearce

    bill pearce TrainBoard Member

    Were I in your shoes, I would look at Z scale. It has a great deal of limitations, most of which are the results of too few modelers using it and companies making bad decisions on what to produce, but in time, I think it will become much more common, much as N has done.
  8. mtntrainman

    mtntrainman TrainBoard Supporter

    Depending on your age...Z Scale may NOT be an option. Sometimes people have problems seeing or working on N Scale stuff let alone Z !!! Like stated...Z Scale "has a great deal of limitations." N Scale has come leaps and bounds over the years...lots to choose from in "N" JMO
  9. John Moore

    John Moore TrainBoard Supporter

    In N scale the default radius is 9.75 and a lot of locos were designed to run on that however that does not mean they look good running on it. However 4 axle diesels look fairly good running on it and 6 axle not so good. And as for steam small 3 axle 0-6-0, 2-6-0. 2-6-2. and 4-6-0 will run on it. Also 0-8-0, 2-8-0 and small drivered 2-8-2s. A 70-85 foot passenger car looks like crap but the 60-65 foot cars look fine. As for freight cars the 40 foot look better. The era of your interest I would suggest the Also RS locomotives. and the F units and the small drivered steam.

    As pointed out Z scale is harder on us older folks however narrow gauge presents an option of N scale locos running on z scale track. But both can be fairly expensive to get into as compared to N scale.

    I made a choice to run switchers as my road power which was not uncommon in the 1 to 1 world but my equipment runs on a 30 inch wide by 14 foot layout and has 8.5 radius curves with some industry track at 7.5 inch radius. I do have steam but it is all small drivered that can run on that curvature.
    MK and Hytec like this.
  10. BigJake

    BigJake TrainBoard Member

    4x8 is relatively huge in N scale, the equivalent of over 7 x 14 in HO.

    That's a nice figure 8 & around layout. If you are modelling using Unitrack, and/or don't have access to slip switches, 3-ways, etc., I would use parallel, back-to-back ladders, diagonally bisecting the yard, using ordinary switches.
    Mark Ricci and Doug Gosha like this.
  11. Mudkip Orange

    Mudkip Orange TrainBoard Member

    40's B&O is an interesting problem because N gauge Pacifics and Mikados will run all day on 12" but you may want to run Mallets, especially EL class.

    I'd stick with 15" and lay it out with easement/spiral curves at each end. You don't necessarily have to draw these in CAD, just leave a few inches of straight after the end of the curve and then offset the straight to the outside of the curve a bit when you're drawing it out on the table.

    The video you posted has some nice gradual transitions which contribute to the trains running smooth and looks great as well.
  12. BigJake

    BigJake TrainBoard Member

    Good advice on easements, and they aren't just for flex or hand-laid track; you can create easements with sectional track too.

    Just increase the radius of the entering & exiting sections of a curve (that connect to straight track), and reduce the radius of the middle sections of the curve to compensate for the space required, if necessary.
    CSX Robert and Doug Gosha like this.
  13. CSX Robert

    CSX Robert TrainBoard Member

    I've been doing that for years on sectional layouts and I don't understand why it's not more common.
  14. Shortround

    Shortround TrainBoard Member

    Makes very good sense to me. Hope I remember that when I can get started.
  15. BarstowRick

    BarstowRick TrainBoard Supporter

    I like what you are trying to do.

    You have to know your limitations. HO doesn't work well with the standard 15"& 18" curves. Unless you limit your self to 0-6-0's or four axled diesels. 40' foot cars and short (I mean short) passenger cars.

    Oh, I tried and don't think I didn't. I built a dozen layouts on a 4x8. So, did other model railroaders I know. We loved those layouts. Possibly more then the complicated layouts that came along later. If you follow me here.

    Here it comes. I like to repeat something said to me by a mentor of mine, "Wider Curves are The Best Curves".

    With that said, enjoy your layout. If you find a way to increase the size, then by all means go for it.
  16. acptulsa

    acptulsa TrainBoard Member

    Everybody seems to have assumed you're ready to give your HO the heave ho. So to speak.

    Yes, you can run great big little bitty articulated steam around a 4x8 in N, and put enough cars behind it to make it work too. But you can also fit 22" radius on a 4x8. That only leaves a couple of inches margin for error, meaning it's easy for derailed cars to hit the floor. And proper 80-85' passenger cars still only barely make it around, showing entirely too much of their ends and diaphragms in the process.

    But it is an option. No, a four foot wide board does not absolutely limit you to four axle forty footers for life.
  17. BigJake

    BigJake TrainBoard Member

    I'm with the crowd that says a layout you cannot reach across requires too much space, since you have to have access to both sides.

    I can barely reach across a 36" HCD N scale layout at table height, just to retrieve a locomotive/railcar (but I have to move it away from the wall to work on the far side, or re-rail the loco/railcar over there). If it were permanently affixed to the wall, I would say nothing over 30" deep, or perhaps even 24" if it is near armpit level or higher, unless you have access to both sides.

    If it is permanently up against the wall, but you have access to both ends, and need wider curves, then I would suggest a bent dogbone or figure eight layout that is thinner in the middle, allowing you to reach the back of it in the middle (or from either end).

    Another option to temporarily boost access is a Topside Creeper (used for automotive work under the hood on large pickups/SUVs, etc.)
    Mark Ricci likes this.
  18. Inkaneer

    Inkaneer TrainBoard Member


    That is not an easement. An easement is a continuous curve of either increasing or decreasing curvature. Using sectional track of different radii does not result in an easement but rather two or more different curves. If the desired result is to turn the track 180 degrees then the only way is to use sectional track of the same radii. Larger radii track has a different degree of curvature than smaller radii and combining the two will not result in a 180 degree half circle. See this chart:

    Degrees of Curvature (
  19. acptulsa

    acptulsa TrainBoard Member

    That's true, but it does help a little. Maybe we should name it. Poor man's easement? Flexphobic easement? Cheeseyeasment?

    That isn't necessarily true, but it is an important consideration. Some radii do define the same number of degrees of curvature, some don't. Most sectional track comes in a variety of lengths, and all of it can be cut.

    If one uses two different types of sectional track which both require the same number of pieces to make a complete circle, then one can be substituted for the other in the most elementary way. No brain cells required. But even if not, four pieces of sixteen-to-the-circle broader curve track can be substituted for three pieces of twelve-to-the-circle track. No cutting would be required, but some figuring is.

    Also remember that your semicircle will grow in diameter. The diameter won't grow as much as the radius does. I know, that last statement probably has Euclid rolling over in his grave, but we are no longer talking about a semicircle, but half an ellipse. The distance across from one straight track to the other will be less than twice the distance from those straight tracks to the end of the layout.
  20. mtntrainman

    mtntrainman TrainBoard Supporter

    My head hurts !!! o_O

    I subscribe to the K.I.S.S. theory...:whistle:
    Mark Ricci and Shortround like this.

Share This Page