C&S B-3-C's

Michael,
The drivers under #40 as well as the other class B-3-C moguls was 40", as Rick stated.
#22's driver diameter, class B-3-B, was 38".
Incidentally, the large boilers the B-3-C class (#4-10) carried after being rebuilt, and the higher steam pressure, which matched the B-4-F class at 180 psi, drove the tractive effort to almost 20,000 lbs, which was higher than several of the 2-8-0's.
There was a statement made here recently that #9 would be capable of pulling only 2 cars at the Georgetown Loop. This is a common misconception. The B-3-C's could pull 4 cars at full tonnage on a 4%.
This class was very stout, and held their own in freight service with 2-8-0's on the C&S for many years.