NZR Locomotive Types
NZR locomotive Wheel Arrangements
All locomotive types are now defined by systems that records the pattern of their wheel arrangement. Their are two primary systems in use, the American and the Continental, the American based on counting wheels, and the Continental based on counting axles. The American system only caters for steam locomotives, while the Continental has both a steam locomotive system and a more comprehensive system that caters for steam, diesel and electric.
A standard locomotive has three groups of wheels (excluding the tender); the ones driven by the pistons, commonly called the Drivers, and a group in front of those, and a group behind, usually referred to as leading and trailing trucks (or bogies). The leading truck is quite important in stabilising the front end of the locomotive, guiding it more gently into curves at speed. The trailing truck (if present) helps carry the load of the firebox which, if wide, will not fit between the drivers, so it can then be placed above the smaller wheels of a trailing truck and be supported by it.
So a standard wheel arrangement is composed of three numbers and for a "Pacific" class locomotive expressed in the following way: 4-6-2, for a 4 wheel leading truck, 6 driving wheels, and a single axle trailing truck having 2 wheels.
There are additional letters that can follow the 3-number code and those used in New Zealand are T for a Tank Engine, or ST for a Saddle Tank engine, so we have 0-6-0ST for the F class saddle Tank engines, which were also a very successful New Zealand locomotive.
There are other less common groups of engines of which NZR had two, the most well known are the Fairlie locomotive, of which two were the first 3ft 6in gauge locomotives in New Zealand, and later classified 'E'. They have two independent power units on separate bogies, so end up with a 4-number code and in this case they are 0-4-4-0 representing no leading truck, 4 driven wheel followed by 4 more driven wheels, and no trailing truck. In 1906, NZR's experimental E class was similarly notated although this was classified as a Mallet locomotive due to among other things, only one power unit being on a bogie, the other being fixed to the locomotive chassis.
The other group to locomotives represented in New Zealand is the Garratt locomotives. Looking at them you can see that they look like two locomotives sharing a single large boiler between them, and that is exactly how they are notated, 4-6-2+2-6-4. you can see this as two groups of the 3-number code joined with a plus sign. When the Garratts proved unsuccessful, each power unit received its own boiler and became a G class Pacific, of the standard 4-6-2wheel arrangement.
With the Continental System there are two styles for steam engines, the original that counts axles in each group (rather than wheels as in the American system), and the newer method which also caters for diesels and electric locomotives. It uses a letter/number system to denote driven and non-driven axles. Here A, B, C stand for 1, 2 and 3 consecutive driven axles and numbers represent idling axles i.e. 1, 2, 3 represent consecutive idling axles in a group. To differentiate Diesel and Steam locomotives, the Diesel loco's are either Bo or Co for 2 or 3 driven axles in a bogie, there are no 4 driven axle examples. Returning to our Pacific class example, it would be written as 2C1 and the F class as C.
For a more in-depth look at the both systems, please refer to the page Locomotive Wheel Notation
Steam Locomotives
NZR used a wide range of steam locomotive types, particularly in its formative years. While every 'type' has one or two formal classification codes, not all of them have class names, however, there is one name in particular that has stamped its mark in history as being a pure New Zealand design and that is the "Pacific". Born from the need to develop more power from the existing narrow gauge "ten-wheeler" locomotives (4-6-0), NZR ordered 13 wide fire-box versions configured as a 4-6-2, which had never been tried before. These were over-all a successful locomotive, from which the A and W classes (and consequently sub-classes) evolved, which went on to become the work-horses of the mid-range engines for New Zealand up until the end of the steam era. In Britain in particular the Pacific type locomotives were developed to an extremely fine locomotive of which the "Flying Scotsman" was the first steam locomotive to break the 100m/h (161 km/h) barrier in 1932, and the "Mallard" also a Pacific class, which reached a top speed of 126m/h (203 km/h) a few years later. These were the pinnacle of British steam locomotive engineering, all based on the Pacific 4-6-2 design originating from New Zealand.
Locomotive classification is then a means of grouping engines of the same general characteristics, and while New Zealand experimented with an earlier classification based predominantly cylinder diameter, it soon adopted wheel configuration as a more practical method, as that was often indication of a locomotives function. Why the American method was adopted in New Zealand is not known.
The following table lists all the steam locomotive Types used in New Zealand in ascending order of by Driven axles, Front axles, Rear axles, showing also the Type name (if it had one) and the number of locomotives of that type that operated in New Zealand
| Wheel arrangement |
Type Name | NZR Classes | Total Number |
Continental Code |
|---|---|---|---|---|
| 0-4-0T | - | A, D, S(1876) | 15 | - |
| 0-4-0ST | - | A, D | 12 | - |
| 0-4-2T | - | H | 6 | - |
| 0-4-2ST | - | C | 15 | - |
| 0-4-4-0T | Fairlie | B, E | 10 | - |
| 2-4-0T | - | L | 10 | - |
| 2-4-2 | Columbia | K(1878) | 8 | - |
| 2-4-4 | - | Q(1879) | 13 | - |
| 4-4-0T | - | La | 3 | - |
| 4-4-0ST | - | G(1875) | 6 | - |
| 0-6-0T | - | F, M, Y | 95 | - |
| 0-6-2T | - | Fa, Fb | 20 | - |
| 0-6-4T | - | S(1882) | 7 | - |
| 2-6-0 | - | J(1875) | 32 | - |
| 2-6-2 | Prairie | N, Na, Nc, V | 29 | - |
| 2-6-2T | - | W, Wa, Wh | 16 | - |
| 2-6-4T | - | Wab, Wb, Wd, Wf, Ws | 101 | - |
| 2-6-6-0T | Mallet | E(1906) | 1 | - |
| 4-6-0 | 10 Wheeler | U, Ua, Ub, Uc, Ud | 49 | - |
| 4-6-2 | Pacific | A, Aa, Ab, Ad, G(1932), Q | 220 | - |
| 4-6-2+2-6-4 | Garrat | G(1929) | 3 | - |
| 4-6-4T | - | We, Wg, Ww | 73 | - |
| 2-8-0 | Consolidation | O, Oa, Ob, Oc | 10 | - |
| 2-8-0T | - | T | 6 | - |
| 2-8-4T | - | Wj | 1 | - |
| 2-6-2 | 12 Wheeler | B, Ba, Bc | 21 | - |
| 4-8-2 | Mountain | J(1939), Ja, Jb, X | 109 | - |
| 4-8-4 | - | K(1932), Ka, Kb | 71 | - |