Wednesday, February 16, 2011

Desirable Weight for Wagons and Coaches

For optimum running qualities, it is desirable to have a relatively consistent weight for wagons and coaches, based on their length. 

For many years, the NMRA in the US has published a standard for wagon weights, which for HO is 1oz + 0.5oz per inch.

One approach for Sn3½ would be to adopt the NMRA standard "as is".  There is nothing wrong with this approach although some people feel that the NMRA standard is a little on the heavy side and it is sometimes difficult to achieve the recommended weight.

I generally use Metric measurements, so I initially converted the NMRA HO standard to metric, which worked out to:

28 g + 0.55 g per mm.

By rounding the numbers down slightly, e.g. to:

25 g + 0.5 g per mm 

the result is a simple formula which is about 10% under NMRA.

  1. GH 4-wheel wagon which is 86 mm long.  The "rounded" formula gives 68 g compared to 75 g based on the NMRA formula.
  2. VF bogie wagon which is 172 mm long.  The "rounded" formula gives 111 g compared to 123 g based on the NMRA formula.


  1. G'day Richard :)

    I agree with you on the NMRA standards being too heavy for Australia, particularly for four-wheelers. Over here on t'other side, a good proportion of us also use a modified version of the NMRA standard, though in this case we just ignore the initial 1oz and just use the 0.5oz per full inch formula (we have been using it for a long time!) which seems ideal for steam-era NSW at least! I've been told that the reason the NMRA recomended weight is so heavy is that the Yanks had very free rolling bogies, even back then when the standards were set, and their vehicles had to have a resonable amount of weight/inertia so the Kadee couplers would work properly! (Free rolling vehicles haven't been a problem over here till quite recently! ;)

  2. Hi Richard, I weighted my four-wheel open wagons - GE, GH etc, with lead sheet from Bunnings and found my P class couldn't haul the train lengths I wanted - 15 4w + van, up my recently-laid helix with a 1 in 70 grade ! I originally put the weights in to avoid jack-knifing while shunting, but have taken them out now and the P now hauls 12-14 plus van up the helix, similar to what the real one did up through Swan View, if you look at the Load Tables.
    I found it more important to ensure the two axles line up parallel, and made a jig up to do this, which fixed the jack-knifing problem.
    The relatively new Kadee Whisker couplers also require less force to couple.

  3. The NMRA standards were designed decades ago before the era of pinpoint axles and the like. The important thing is consistency of weight and so the heaviest wagon in your fleet will to some extent determine how heavy you make the rest of them. In the old Scalefour manual they recomended a minimum of 1 oz (i.e about 30g) for a 4mm scale 4 wheeler but some whitemetal kits could be twice this.