Minimum Radius Required?

Discussion in 'HO Scale Model Trains' started by TruckLover, Sep 13, 2008.

  1. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    hey guys, I got my ribbonrail track alignment gauges. I set up a 32" for the outside track and a 30" for the inside track on one corner of my main line. Its huge for my shelf's :cry:

    It works and i could get away with it possibly but that wouldnt leave room for to many switches to branch off for industry.

    My question is, what is the smallest radius i could get away with? I will be running SD90MAC's.... BIG Locos but nothing bigger then that. Biggest rolling stock will be Double Stacks (Singles, 3-unit and 5-units; Walthers, Athearn, Kato, Intermountain and Atlas). Could i get away with 24" inside, 26" outside for mains? Will that work? I dont necessary care for too much realism, as i know the bigger the radius, the better the train will look. I just care mostly about getting the most out of my 18" shelf's. Mainline runs along the front edge of the shelf's, so in the corners, mainline tracks are aloud to hangover the corners where the shelf's meet at 18" and i will build pieces to support the tracks that overhang.

    Could i make it with 24" and 26" running Large Locos and Double Stacks?

    Thanks in advance for any advise
  2. UP SD40-2

    UP SD40-2 Senior Member

    Josh, yes, you COULD get away with 24R and 26R curves:thumb: , true some of the cars and engines wont look to pretty going on those curves:oops: , but what you are running WILL WORK on those radius:winki: .
  3. sumpter250

    sumpter250 multiscale modelbuilder

    You may have to go with a bit more distance between the rails, to account for the combined overhang of the loco, and rolling stock on the other track.
    When I run my B&O EL3a on the modular layout, I have to keep it on the outside track, the boiler hangs too far out and collides with trains, if I run it inside.
    tack down a test curve to check clearances before laying track.
  4. Russ Bellinis

    Russ Bellinis Active Member

    The best way to find out what radius a particular locomotive will operate on reliably as well as to make sure your scenic details clear is to make a track on a piece of board to the desired radius. Put on a locomotive and the longest car it will pull, and test run it to make sure the locomotive will negotiate the curve and not derail the car it is pulling. Also measure the overhang to both the inside and outside of the curve to make sure you leave adequate clearance on both sides of the curb.
  5. Kevinkrey

    Kevinkrey Member

    Find a radius to work. You know the string trick, thats what I did. You can do it that way and find a radius thats between looks good and performance.
  6. green_elite_cab

    green_elite_cab Keep It Moving!

    I'm pretty sure you have nothing to worry about with those radius curves. They are about as broad as you can realistically put on a most model railroads.
  7. shaygetz

    shaygetz Active Member

    I run AHM/Rivarossi articulateds on 20" radius. It's a hoot to watch but it can be done...:thumb:

  8. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    Thanks everyone for your tips and ideas :mrgreen: :mrgreen:

    I will make sure to have plenty of space between the tracks to account for train overhang :thumb:

    I also ordered 2 more ribbon rail track alignment gauges for 26" and 28" also :mrgreen: so now i have a whole set of 20", 24", 26", 28", 30", and 32"
  9. pgandw

    pgandw Active Member


    The NMRA Recommended Practice for curve radii (RP-11) are at

    The Layout Design Special Interest Group (LDSIG) (link is down right now) has a rule of thumb. The rule of thumb recommends for mechanical reliability a minimum radius of 3 times the length of the longest car or engine, measured over the center of the coupler.

    The NMRA RP-11 takes appearance into account; the LDSIG rule of thumb does not. Both are conservative - they will work with rolling stock and locomotives that have little-to-no special provisions to go around sharper curves. The rule of thumb assumes body mounted couplers and decent under body detail.

    Can you get by with smaller minimum radii? Yes, in most cases. As you get further away from the rule of thumb or RP, the number of specific pieces of rolling stock that won't take the curve increases. Brass steam locomotive models are often the 1st casualty. Most non-brass rolling stock and locomotives will get to 2.5 times length without issues. Next to fail will be full scale 80 or 85 ft passenger cars with full underbody detail and no special coupler arrangements (Walters HO passengers cars sometimes fail on 24" radius).

    As one of the other posters said, if you are going to vary significantly from the recommendations, you need a test program. The sharper the curves, the more testing will be required for reliable operaion. Be prepared to make modifications to underbody detail and perhaps switch to truck mounted couplers if you are going to the 2 times length range.

    A final thought - minimum radius has a great impact on the reliability of a helix or the ability to run long trains without stringlining. The 3 times length rule prevents failure in these 2 cases.

    my thoughts, your choices
  10. RobertInOntario

    RobertInOntario Active Member

    I've got some curves that are around 17"R (or less) on my 4x6' layout! I have an outer loop that basically uses 18" to 20"R curves and an inner loop with 17"R -- these might even be tighter as I haven't properly worked out their radii! I obviously have to go with what works for the space that I have, as opposed to realism. Rob
  11. 60103

    60103 Pooh Bah

    Josh: I've noticed that curves look sharper viewed from the outside and broader viewed from the inside. This is good news for a shelf layout. You may still think your rolling stock looks funny on the sharp curves.
  12. Kevinkrey

    Kevinkrey Member

    He just HAD to go and get an almost all container car fleet didnt he?:mrgreen: Ya know, my short little ore cars look fine on the smallest of curves.:cool:
  13. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    Thanks Fred, Rob, David, and Kevin for all the advise and info :mrgreen: :mrgreen:

    hehehehehe there will be many more wells to come :mrgreen: I plan on getting all 3 of the KATO Maxi IV's and all 11 (11 because KATO and Intermountain have decided to do the same road # on one set of the cars lol) of the Intermountain Maxi IV's in the BNSF Paint. Thats another 42 wells :mrgreen: :mrgreen: added onto my 29 TTX Wells :mrgreen: :mrgreen: :mrgreen:
  14. wjstix

    wjstix Member

    I have 16" wide shelfs and used a Kato Unitrack 31" R curve at the corner with plenty of room to spare. I'm sure I could fit in a second track with no problem. On straight shelf sections you should have room to put in industries even if you use double track, but you might have to be creative - use flats where possible, or widen the benchwork a few inches for a foot or two.
  15. diburning

    diburning Member

    At the club, the industrial branch's horseshow curve has a radius of about 16' maybe less. I can get Superliners over it if I'm going slow. Another member has a DD40X and it does ok with the 18" curves in some places. (it overhangs by a lot, but it makes it without derailing)

Share This Page