In the beginning of steam traction, locomotives usually had two axles. In the simplest form, either the front or rear axle is being driven by a pair of cylinders. But very early on, there was the idea to power both axles for increased pulling power. The initial approach was to couple both axles via gear wheels. A solution that soon found widespread acceptance was to couple the axles via coupling rods. With a total of two axles, possible wheel arrangements are being called 0-2-2, 2-2-0 or 0-4-0 in the Whyte notation.

When trains became heavier and had to be accelerated, three-axle locomotives were born. One argument for a third axle was that the additional unpowered axle increased guidance on the track, increasing running characteristics both in curves and at high speeds. Norris was already using a two-axle leading truck to improve guidance on poorly laid track. Another point to add another axle was the additional weight that could be carried, what allowed to mount a larger boiler. This led to the wheel arrangements 2-2-2, 2-4-0, 0-4-2 and 4-2-0. Later developments with only one driving axle were motivated by the absence of friction losses being caused by two coupled axles.

In some countries, passenger or express locomotives with only one driving axle were built up to the end of the 19th century. There was a huge number of single-driver locomotives with wheel diameters of more than two meters or six and a half feet. Notable designs included the Crampton that set speed records in the 1840s, but also many 2-2-2 locomotives also reached very high speeds. In the last three decades of the 19th century, 4-2-2 locomotives with a leading bogie achieved very high average speeds with light express trains. This was also possible due to steam-powered sanding gear that also allowed starting on wet rails.

Besides these single-driver locomotives, four-coupled designs (what stands for two driving axles) dominated passenger and express traffic worldwide until the turn to the 20th century. Most European countries had a widespread preference for the 2-4-0 with a single leading axle that was usually fixed in the frame. In the USA, where tracks were often cheaply laid due to the long distances, the 4-4-0 was the ubiquitous allrounder that profited from the two-axle leading truck.

While growing train weights in freight traffic often necessitated six-coupled locomotives from the 1870s, four-coupled passenger locomotives with a trailing axle allowed to install a powerful boiler with a huge firebox to be combined with adequate adhesive weight. Although the 2-4-2 only had a short career and was mostly viewed as an alternative to the 4-4-0, the 4-4-2 “Atlantic” took the reign in express service. There were many designs with top speeds in excess of 80 mph or 130 km/h which could also haul a train of more than ten wooden four-axle cars at sustained speeds of more than 60 mph or 100 km/h.

It took until the turn of the century that heavier steel cars prompted the introduction of six-coupled locomotives in passenger service. 4-4-0 and 4-4-2 locomotives were relegated to commuter service, while the remaining 2-4-0 locomotives had their last years in service on secondary lines. Nevertheless, there were some experiments with four-coupled locomotives with two-axle trailing trucks in the 20th century and some streamlined designs were built as a 4-4-2. While they still could develop a high power and could reach high speeds with light trains, it quickly became evident that they had problems with starting heavy trains.