Track Radius

Discussion in 'N / Z Scale Model Trains' started by TruckLover, Sep 23, 2006.

  1. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    N-Scale Track Radius

    So what should it be in order to run big diesels and some long cars. Some of the big diesels I want to run are SD75M, SD90MAC, AC4400 ....... and the biggest cars I want to run are centerbeam lumber cars (73'). (I won't have any big huge long autracks, boxcars, or flatcars)

    What should my mainlines and most sidings with cars that are longer than 50' be?

    Thanks in Advance. :D :)
  2. Amtrk14

    Amtrk14 New Member

    22" should be fine. I have 22", and my SD70MAC's, AC4400CW, etc. run good on them. If you have the room, I would go with something a little bigger...possibly 26" Radius.

  3. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    Thanks Sean, but I forgot to say I need to know for n-scale.:oops:
  4. Amtrk14

    Amtrk14 New Member

    Can't help you there, as I run HO. Sorry.

  5. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    Thats ok, I run HO too and this is going to be my first N-Scale layout.

    Thanks Anyway
  6. pgandw

    pgandw Active Member


    The Layout Design Special Interest Group has a rule of thumb that applies to all scales. It says for reliable tracking with body mounted couplers, the minimum radius should be 3x the length of your longest car, measured from coupler face to coupler face. A 73ft car in N will be close to 6" long; this puts the minimum radius guideline at about 17".

    If you want improved looks, go to 4x car length, and for automatic coupling to work on curves, and even better looking, go to 5x car length.

    With truck mounted couplers, my experience says that you can go down to about 2.5x car length without much trouble. After that, you will have to test each piece individually, make modifications, and of course the overhangs will be terrible.

    Reality is that the longer N cars take just as much space (length and radius) as 40ft and smaller cars do in HO.

    my thoughts, your choices
  7. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    Thanks Fred, That really helps :D :)

    I think that im going to go with about 17-19" radius on the mainlines and sidings that will have longer cars and 14-16" radius on sidings with cars 50' and under.

    Thanks Again!!!:thumb: :D
  8. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    Ok, now here's my next question, for the switches, should I go with #5's, #7's, or #10's?

    Could I do #7's off the mainline and on the sidings with bigger/longer cars and #5's on sidings with smaller/shorter cars


    do I need #10's off the mainline and on the sidings with bigger/longer cars and #7's on sidings with smaller/shorter cars??
  9. pgandw

    pgandw Active Member


    The NMRA RP 12.7 for turnouts is at

    The closure radius (row (11)) is the key to choosing turnout number to match your curve radius. It it the radius of the curved part between the frog and points. The closure radius is NOT a substitution radius.

    The NMRA RP (RECOMMENDED Practice) for turnouts is very much like US prototype turnouts. There is NO requirement for manufacturers to follow the RP. A manufactured #5 turnout could be anywhere from about a #4.3 to a #5.7, depending on the individual manufacturer. If you can find out the actual frog angle, you make a good guess as to what the closure radius might be. For instance, the Atlas HO #4 is really a #4.5, and has a 22" closure radius instead of the 16" closure radius of an NMRA #4.

    Peco turnouts (unless specifically US prototype), and the Atlas Snap Track turnouts (at least in HO) have curved frogs, and are pretty much a constant radius throughout the curved leg of the turnout. You would have to find out what that radius/is was to judge whether they would be useful or not in your situation. I would guess the Peco "small" and the Atlas Snap turnouts would not work for you.

    From the NMRA chart, anything from #6 and up would work on your main line. On your other trackage, a #5 might be a little tight (13.75" closure radius) but will probably work at low speeds. Remmber the curved portion is quite short, so most rolling stock will not have both trucks on the curved portion at the same time. Thus, the turnout will not seem as sharp as it really is if the frog is straight.

    my thoughts, your choices
  10. nolatron

    nolatron Member

    For my nscale stuff, I stick to no less than 19" radius curves and #6 turnouts.

    Anything less than 19" and my 6 axle diesels will toss cars off the tracks, jump the track itself sometime, and if you have stuff like multi-unit intermodals they'll possibly get stuck going around the curve if it's two tight.

    I made this mistake on my very first layout with using two tight of a curve, so since this I've stuck with 19" or higher.
  11. TruckLover

    TruckLover Mack CH613 & 53' Trailer

    WOW, thanks Shaun and Fred,

    Shaun: Thanks for that info. I do want to run 6 axle disels so I might just go with 19" now.

    Fred: Thanks for all that info on the switches, it really does help!!:thumb: :D
  12. Triplex

    Triplex Active Member

    The SD75M and AC4400CW are the same length as the centerbeams. Your governing engine will probably be the SD90MAC, at a scale 80' long. The only plastic one around is the Kato model, and I've heard extremely variable values for its minimum radius.

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