Boeing 737 MAX
Boeing spent a lot of 2011 looking at two different diameters of CFM International LEAP-1B engine:  or . Both of these would mean that Boeing would have to make some changes to the wheels, because the engines need to be  above the ground. Boeing said the bigger engine would use less fuel. However, because it is bigger, it would make more drag and be heavier. This would mean that even more changes would be needed.