What are cast-iron spoked wagon wheels?

Cast iron spoked wagon wheels date back to the 1830s and were the mainstay of wagon wheels for nearly 100 years.

Wagon wheels of this type had a diameter of around three-foot and usually featured eight spokes. A variant measuring three-foot six inches with ten spokes was produced for some passenger stock and freight wagons designed for higher speeds. The wheels were cast in a single piece from iron with a wrought-iron replaceable tyre.

By the mid-1920s, steel disc wheels were starting to appear on wagons, but the mainstream production of cast-iron spoke wheels continued for another decade. Astonishingly, despite new spoked-wheel production slowing to virtually nothing by the mid-1930s, examples could still be seen in service as late as the 1970s.

One of the problems with cast-iron wheels was their tendency to develop cracks and fractures. This happened a lot due to the forces and heat exerted on wheels, particularly on braked stock where the brakes made direct physical contact with the wheel. To catch any such defects before disaster struck, the railways employed wheel tappers to frequently walk the length of trains tapping the wheels with a hammer to listen for abnormalities. A dull, flat response to the hammer blow would indicate a defect resulting in the vehicle being removed from service. By the late 1930s, a combination of better manufacturing techniques and the introduction of disc wheels was sufficient that wheel tappers were seen less and less until they disappeared from the scene altogether.