Included in Bulleid's innovations were the wheels. Most British steam locomotives have spoked driving wheels, but our engine is different. The wheels are a corrugated disc, know as a BFB wheel. BFB stands for Bulleid-Firth-Brown. The wheels were designed by Bulleid, but the steel company of Firth Brown designed the method of manufacture. They are cast in one piece, and the moulding was quite complex, so Firth Brown were included in the patent.
The rim of a spoked wheel is stronger by each spoke, and therefore weaker between the spokes. The BFB wheel doesn't have this disadvantage, so there is less chance of the tyre slipping. They are also lighter by about ten percent compared to a spoked wheel of the same diameter. They do, however, collect water, oil and sand in the hollows.
The smaller wheels, including those on the bogie and the tender, are of a similar design.