Maybe I need to step in here to add some clarity:
The issue is: How much road force is too much?
1) Different vehicles have different sensitivity. Not only are small vehicles more sensitive than large vehicles, there are some vehicles that are way, way more sensitive than others of the same size. There are certain year/make/models of cars where hardly anything is acceptable. And there are certain year/make/models where practically everything is OK.
2) Some people have sensitive butts! Enough said about that!
3) Rough roads can hide a lot of vibrations. So if you live where the roads are subject to winter freezing and thawing (and that causes the road to heave unevenly), wheel end vibrations have to be quite large to be felt. But if you live where the roads don't freeze, even small vibrations are detectable.
What I am trying to say is that there isn't a single answer to this question. Sure, there are values where it generally doesn't matter about those 3 things listed above. AND there are values that will ALWAYS cause a detectable vibration.
But in between those 2 values is a very wide range. I've done a lot of investigations and I just don't feel comfortable offering a value. What I do is look for the outlier. Generally, there is one, and on occasion, 2.