The best-known locomotives were those on the Denver, South Park & Pacific, and they rostered fairly large Mason Bogies, mostly of 2-6-6 and 2-8-6 wheel arrangements, and had a lot of success with them. Some of these locomotives were later sold to the Burlington and Northwestern Railway, a CB&Q subsidiary in Iowa. Another problem with the Fairlie design showed itself in Colorado, the surprisingly poor tracking of the powered bogie. It would both hunt, or wander, when on straight track, yet provide more resistance to turning when it hit curvature than might be thought. This manifested itself in much greater wear on wheels and track than might have been expected.