All very reasonable Machka. And hitting the right mark, like you say, is mostly about previous experience. For me, most of my tours are in fact starting at the end of my driveway. But I get your points. All those factors are important.

My interest in the math side is probably somewhat academic. I don't expect it to deliver a recipe for my behavior. But I'd like to be influenced by it.

Edit: I think half your weight is an interesting idea. At that level my pack is only a "little" heavy. (Weight 150, pack 80). No, I re-read what you said. Mine is very heavy since I'm not counting the weight of the bicycle there.