Questions on Turning Radius

Discussion in 'HO Scale Model Trains' started by bryandjen107, Dec 30, 2006.

  1. bryandjen107

    bryandjen107 New Member

    Hi All,

    I just started in the hobby and I have ANOTHER question for the smartest message board on the net. Are there turning limitations to certian loco's. I am talking about HO. I understand the math, but what can I look for when buying a loco to determine what the ideal turning radius is? I would like to verse myself in this informationbefore investing in individual pieces.

    Thanks for all of your help,

  2. CRed

    CRed Member

    From what I have gathered since joining this board is,if your radius is 18"-20" you'll want to stick to 4 axel diesels and a mininum 22" radius for 6 axel diesels.For steam anything larger then a switcher you'll probably want 24" or larger.

  3. LongIslandTom

    LongIslandTom Member


    General rules of thumb for HO:

    - Small locomotives such as 4-axle diesels and steam engines with 3 driver wheels or less can negotiate 18"-radius curves.

    - Larger locomotives such as 6-axle diesels and steam engines with 4 driver wheels or more usually works best on 22"-radii or bigger. Some might be able to get around 18"-radius, but it's a crapshoot.

    There are exceptions of course. Best ask in the forums if in doubt.

    Basically, the bigger you can get your radii, the nicer it will work and look.

    Good luck.
  4. pgandw

    pgandw Active Member

    See my comments on the opportunities presented by 18" radius curves on this thread:
    Long Island Tom rules of thumb are pretty accurate for HO locomotives.

    The only addition I have is that full scale length passenger cars - both heavyweight and streamline - generally need at least 24" radius curves, and bigger (28"-30") is much better. There are exceptions that will do less, but to use Tom's words, "'s a crapshoot." The same applies to modern long freight cars.

    my thoughts, your choices
  5. Glen Haasdyk

    Glen Haasdyk Active Member

    As perviously stated a smaller steam or diesel will negotiate an 18" radius curve. However, adding a turnout in an 18" radius curve is usualy not recommended. I found the hard way when building my layout that trains love to derail on 18" raduis curves with turnouts in them.
  6. 60103

    60103 Pooh Bah

    If you get into som of the more expensive lcocs, like the brass imports, the minimum radius may be even larger. The detail parts start to limit how far the trucks will turn, and the pilot trucks on steamers will hit the backs of the cylinders. If you're spending over $100 on a loco, check reviews in the magazines where they should specify a minimum radius.
  7. Jim Krause

    Jim Krause Active Member

    Definitely. As stated above by several people. Two considerations, first, physical ability to negotiate the curves due to length and the number of drive wheels, in the case of steam locomotives. (this was a consideration on the prototypes too) and secondly appearance. If you want your layout to replicate the real thing, you need larger radius curves so the equipment doesn't hang over the track on the inside of the curve and uncouple itself or derail on the outside of the curve.
  8. 60103

    60103 Pooh Bah

    prototype steam locomotives had minimum radii in the 800-1000 foot range. This translates to 9 feet and up in HO. So a lot of compromises are built in to any reasonable model. An unreasonable model, with scale tolerances, would probably run straight down the track and straight off the curves.
  9. Triplex

    Triplex Active Member

    When it comes to steam, the real issue isn't number of drivers, but rigid wheelbase. Eight-coupled engines with small drivers (all 2-8-0s, most 2-8-2s, etc.) will have no trouble on 18". It's 4-8-4s and the like that you have to be concerned about. Their prototypes were designed for high-speed service, and thus have large diameter drivers, thus a longer rigid wheelbase. This is why a 2-10-0 can often get round tighter curves than a 4-8-4 - since the drivers are smaller, the rigid wheelbase isn't longer, and the overall engine is smaller.
    With brass, a larger 6-axle diesel may absolutely require 30", and the biggest steam power 42" to 48".

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