Before plastic kits appeared, most model rolling stock, whether consisting of four-wheeled open wagons or twelve-wheeled dining cars, was heavy. In addition, the common use of wheelsets with large diameter axles running in white metal bearings produced a high rolling resistance. A really powerful and heavy loco was needed to move a 25 wagon train, or one of ten coaches. A typical wagon of that period would weigh 180g (6.3oz) and have a rolling resistance of 6g (0.2oz), a coach weighing 1000g (35oz) would have a resistance of 30g (1.1oz).

The coming of plastic kits and the general use of wheels with axle journals of 0.070in. diameter or less running in low friction bearings brought a dramatic reduction in weight and rolling resistance. Wagons now weighed as little as 55g (1.9oz) with a resistance of less than 1g (0.1 oz). Longer trains could now be hauled and locomotives did not have to be so powerful. Backing such stock however, especially in long trains, often brought trouble.

If good and consistent running, especially when propelling, is to be obtained, vehicles must be accurately and soundly constructed and free running. This is fundamental; equalising or springing, correctly applied, will help lighter wagons to overcome track deficiencies, but gross weight is critical in the prevention of derailments. When propelling, this applies particularly to the wagons nearest to the locomotive, since they are being pushed against the mass of the train and its resistance to rolling. If small trains are the invariable rule on a particular line, reduced weights may be considered. However, such stock is likely to be less reliable if run on layouts where long trains are the norm.

During the tests that produced train resistance data, very light wagons were found to be prone to derailment. From these experiments a guideline can be recommended for which the standard gauge 4-wheeled wagon of 18ft to 19ft in length and having a 9-10ft wheelbase (125mm in model form) is the basis. The increase in weight for increasing length is 25g per 25mm, or 1oz per inch. This caters for longer wagons, 6-wheeled stock and bogie stock, including coaching stock and, conveniently, is roughly 1g for each 1mm of vehicle length.

In general, it will be found that bogie stock seldom needs additional weight but 4-wheel wagons assembled from plastic kits nearly always do.

We recommended that model rolling stock should weigh not less than 1g per millimetre of vehicle length (equal to approximately 1oz/in) with a minimum weight of 125g (4.4oz).

Compiled by the Technical Committee for the Gauge O Guild Manual, and adapted for the GOGWiki by Nick Baines.