Further clarification on Mz and Mx

Thought about this some more, given that a few people asked about it. Best way I can think of each of them is a dynamic measure of where the force center of the footprint is.

When making a simple vehicle model you might assume tire lateral force acts right under the centerline of the spindle. This isn't the case. Due to the black magic of tires, the lateral force trails the centerline, which is what gives rise to pneumatic trail and aligning torque. Mz is really a measure of how the pneumatic trail is changing, and where that "Fy action point" is moving around. Since yaw moment is dependent on Fy cross-multiplied by the distance from the "action point" to the CG, the fore-aft movement measured by Mz does affect your vehicle balance.

Likewise with Mx, in a simple model you might assume your track width to be constant or just a function of how much lateral scrub your suspension generates. In reality as the tire deflects under lateral load, the center of pressure ("Fz action point") deflects as well and your track width changes length or shifts over (deflects toward inside of turn). That in turn will definitely modify your lateral load transfer!

Bottom line, they're both important and non-trivial.