Bavarian B I engines were 2-4-0 steam locomotives of the Royal Bavarian State Railways (Königlich Bayerische Staatsbahn).
The Class B I was developed in parallel with the Class A II, but had a coupled axle instead of a second carrying axle.
As a result, it developed a higher tractive effort.
The coupling rods were based on an American prototype.
Later many of the engines were fitted with a Crampton boiler.