Definitely stupid, that is the worst way to save fuel.

Personally, I’m not usually up for getting the best mileage out, but knowing the tips is definitely nice if I know I need to save. Not to mention, the aero mods are beneficial for performance driving too, and it’s a passive thing, which is nice.

Yeah, getting savings from being super close up to a semi-tractor trailer is not worth the risk. Stay minimum 3 seconds back (90m or 300ft at highway speeds). On the bright side, a car flattened by a truck will not use any fuel.

However, pacing with a semi (going at 105km/h or 65mph) from a safe distance behind will still net you savings from not speeding. You can set the cruise control or do whatever fuel saving acceleration pattern you have.

You gotta leave enough room to react and stick out the side just a bit so you can see in front of it just a bit but also you can stop a lot quicker than them.

I generally don't do it with Semis though, and I probably don't get as close as the people you're thinking of. If I'm on a long trip I'll ushally try to find a fifth wheel camper going roughly the speed I want and I'll set my adaptive cruise to the minimum distance. The campers throw fewer rocks.

Also if you're ever drafting make sure to keep an eye on your temperature. Most of the time it should be fine but a hot day and going uphill it could very easily overheat, especially if you've done some of the other hypermilling mods like partial grille block.