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Leading Wheel




The leading wheel or '''leading axle''' of a Steam Locomotive is an unpowered Wheel or Axle located in front of the driving wheels. The axle or axles of the leading wheels are normally located in a truck (or " Bogie "). Leading wheels are used to help the locomotive negotiate curves and to support the front portion of the boiler.

Importantly, the leading bogie does not have simple rotational motion about a vertical pivot, as might first be thought. It must also be free to slip sideways to a small extent (otherwise the locomotive is unable to follow curves accurately - a point lost on the 19th century railway pioneers), and some kind of springing mechanism is normally included to control this movement and give a tendency to return to centre. The sliding bogie of this type was patented by William Adams in 1865 .

The first use of leading wheels is commonly attributed to s, and no Trailing Wheel s. In the UIC Classification system, which counts axles rather than wheels and uses letters to denote powered axles, the ''Jervis'' would be classified 2-A.