Here's a more complete list of differences. The 425 has:
3 additional HP
ROPS
Higher torque wheel motors with matching larger capacity pump to supply them
8" additional lift height
8 " longer wheel base
longer overall length
larger engine compartment easier to work on
2 articulating pistons (only 1 on the 422)
"beefier" articulating joint
more leg room
steering wheel and joystick are higher
larger oil cooler
different hydraulic oil weight
a few pounds heavier
I found the 422 a little easier to get in and out of because of the way the seating area is configured and lack of ROPS. You sit a little higher in relation to the controls on the 422 but there is less leg room due the way the articulating piston is configured. Even though there is more legroom in the 425, I found that my knees were positioned such that they hit the frame more so than the 422. I am 6'2".
There are other differences in engine compartment layout that will be unknown in the future due to the change to the Robins engine. Current Kohler 425 has the metal gas tank mounted on the engine cover and muffler inside the engine compartment. New design to the Robins engine may cause the 425 to be more like the 422 with the muffler outside the compartment and plastic gas tank inside the engine compartment. Terry says these design decisions have yet to be finalized. Either way the 425 has more room to work on the engine.
Thanks go to Trebor as I learned all of this from Terry while using his 425 which was ready to go.
