Texases,
When I mentioned Force and Moment, I am talking strictly about the tire. Toe in is vehicle.
But F&M is one area where I just don’t have the expertise. I know there is a tire force (or moment) that translates into “On Center Feel”, but I don’t know much about it.
“On Center Feel” is a tire property that describes the vagueness (or lack of vagueness) when the steering wheel is pointed straight ahead - that is: How positive does the car feel when it is driven straight ahead. Does the steering wheel feel “centered”? Does it take a bit of force to get the car to deviate from the straight path. Does the car want to return to the straight ahead path?
But in this case, I think the fact that the problem is gradually returning points to something other than the tire. I suspect the vehicle is gradually developing toe-out, and toe-out is basically unstable.