This is something I've been pondering now for a few years. Whenever I drive on the freeway and I'm in the fast lane going at least 10 mph over the limit, I can always count on there being an SUV or pick-up truck suddenly on my tail, trying to force me to move over. Is it the greater horse power, being up higher on the road, the fact that since their vehicle is bigger they're more important? Anyone have any clues?