[Fat Charlie]

Safe following distances change depending on speed, weather, time of day, traffic, etc. I wouldn't get closer to something just because I'm drafting it, in fact I'll generally give it at least as much distance as I would a car because a good truck is hard to see through. If it's big enough to be worth drafting, it's punching a big enough hole in the air that you can do it from a safe distance. Besides, P&G won't let you pick an exact distance anyway.

The worse your car's aero, the more drafting will help. I find that I can get an mpg boost if the rig is going at my speed, and I can hang on to one going around 10 mph more than I want to go without hurting that trip's numbers- but I've found that trying to catch up with one isn't worth it.

I draft a lot less than I used to, but I think that's because I'm pickier about drafting opportunities than I was.