A trailing wheel (or truck or bogie) is a type of support used on a locomotive. It is located behind the driving wheels.
A trailing truck on a PRR Pacific.
They are most commonly used on steam locomotives to support an enlarged firebox. By placing the firebox over smaller diameter trailing wheels, size and firegrate area can be greatly improved while not affecting driver diameter. They can also be used to help guide a locomotive which commonly runs backward through curves. On larger tank locomotives, a trailing bogie would be used to support the firebox, cab, and fuel bunkers. Trailing bogies are also found on some electric locomotives designed to operate forward and backward.
Trivia[]
- The most trailing wheels ever put on one truck totals six, or three axles. This arrangement was used in the wheel arrangements of 2-6-6, 2-8-6, 6-8-6, 2-6-6-6, 6-4-4-6, and the proposed 4-8-6.
- The Atchison, Topeka, & Santa Fe created the 2-10-2 type by adding a trailing axle to its 2-10-0 helpers to guide them backward down the mountains once they finished pushing. This popularized the nickname "Santa Fe" type for this wheel arrangement.
- Steam locomotive manufacturer Lima Locomotive Works used a six-wheel trailing truck on the heaviest steam locomotive it ever designed, the Allegheny 2-6-6-6, to accommodate its "Super Power" firebox. It also planned to use 6 wheel trucks on the proposed Super Power 4-8-6 of 1949.