Quick, Track Radius Question

Discussion in 'N / Z Scale Model Trains' started by TruckLover, Dec 16, 2006.

  1. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    What is the minmum radius I should have for BIG locos such as AC4400 and C44-9W's?

    This is N scale I am talking about.
    • 15"
    • 16.25"
    • 17.50"
    • 18.75"
    • 20"
    • or 21.25"
  2. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    SWITCHES too

    What is the best for big locos such as above for swictchs?
    • #5
    • #7
    • #10
  3. pgandw

    pgandw Active Member

    The LDSIG rule of thumb recommends the following for curve radii (applies to all scales):

    - a minimum radius 3 times the length of the longest piece of rolling stock for reliable tracking. Length is measure from coupling point to coupling point. This minimum radius rule will prevent most all instances of string lining and other derailments from curves that are too tight.

    - a minimum radius of 4 times the length of the longest piece of rolling stock improves appearance significantly.

    - a minimum radius of 5 times the length of the longest piece of rolling stock allows automatic coupling (but not necessarily uncoupling) to occur.

    Note that in N an 80ft passenger car is 6 inches long. If you are running full length passenger cars or other 80ft+ cars or locos, the 3x rule calls for at least an 18" minimum radius.

    The rule of thumb assumes body-mounted couplers. Since most, if not all, N RTR rolling stock comes with truck mounted couplers, you can "cheat" to about 2.5 times the longest car/loco length with good tracking reliability except for increased risk of string lining. If you are going to run long trains up grades, then you will have to stay with the 3X rule to avoid string lining.

    For turnouts, the NMRA RP (http://www.nmra.org/standards/rp12_7.html) gives recommended turnout dimensions for various turnouts. Note that these are recommendations only; most turnout manufacturers have their own dimensions. But it's a good guide that will be within 10% or so. Dimension 11 is the closure rail radius, which is the radius of the curved part of the turnout. This should match or be slightly larger than your minimum curve radius for best use of your space with reliable tracking. A #5 turnout shows a closure radius of 13.75" and a #6 has 22".

    my thoughts, your choices
  4. Triplex

    Triplex Active Member

    A lot of people run these engines on 15" curves. #6 switches are the best to go with those curves, but I gather you're planning on Atlas C55, which doesn't have #6 switches (who designed that system, anyway?)

    By the LDSIG rule given above, since those engines are about a scale 74' long, 3 times that is 222' in scale, or 16.65" to us.

    You sure AC4400CWs are big? Try an SD90MAC. A scale 80' long, they require 18" by the 3x rule.
  5. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    Thanks Fred and Triplex

    For the curves, I won't have anything bigger than a scale 72’ car (Centerbeam Lumber Flat) so I will go with a 17.5” radius will allow for AC4400 and C44-9W and maybe a SD90MAc, plus it will make the smaller AC4400 and C44-9W look better on the curves.

    For the switches, I will be using #7 switches off the mainline and #5 switches for sidings with smaller cars.

    Thanks again for the help guys:D :D :D :D

Share This Page