Safe drafting and impact on mpg
 

I've been wondering how effective drafting behind a vehicle is and if noticeable results can be achieved at a safe distance. Obviously, if I'm 3" away from the bumper of the car in front of me, I'm going to be utilizing their pushing of the air out of my way better than if I'm 100' behind them. But we live in a world where the unexpected happens and you can't safely travel 3" from the back of the car in front of you.

So, is there a safe distance that anyone has documented measurable efficiency gains by drafting leading vehicles?

Safety is a huge factor. Any gains would be erased 1000x over if there is a single safety breach. Also It goes a little beyond that for me in the way of damage from debris from the leading vehicle. Windscreen, headlight, leading edge hood damage impacts from rocks and dirt will out weigh when it comes time to repair.

So, the consensus so far (with one post) is that there is no safe distance at which a drafting gain could be realized.

There is a benefit to using a big rig as a traffic blocker for you. Traveling at a safe distance behind one can allow you to travel at a slower speed without negatively affecting faster traffic as much as you would if you traveled slow without the rig as a blocker. People can see the rig from far away and maneuver themselves around it (and you) in a much safer manner than if they just came upon you suddenly in their way.

I have found very minor benefit from the drafting affect when you are at what I consider a safe distance. I use Scangauge to confirm this. So I don't drive behind a big rig unless I want to drive slower than the rest of the traffic.

i use the two- or three-second rule of following and noticed that drafting helps even at these distances. i only have a vacuum gauge so can't provide any delta-mpg...

Same here, in my Acura, around 1.5-2mpg diff in lean-burn, and 0.2-0.4 out of it.

In my (recently traded in) Dodge 1500, I saw a 4mpg difference. That's not a typo.

Safety is, of course, relative. You're safer at home on the couch. If, as I suspect, I can shed mph faster than the truck, right behind it seems a pretty safe place to be. But road debris is another matter; trucks shed big hunks of tire tread. You see them lying along side the road; they're bigger than a deer.

Yes, I have done it. I prefer a flatbed with a full-width half-height load—less buffeting.

My Jeep Wrangler will gain 2mpg/tank even with only 50% highway. But some of that is at a slightly slower speed. At a 3W distance(3 wrangler) I can hear a large reduction in wind noise and feel the resistance drop. Tankers are best. Any closer and may as well be towed. Rocks, blown tires, eh. What, you want to live forever? Keeps your reflexes sharp.

If you drive on California highways with any amount of traffic, you are already drafting "at dangerous following distance", and I'd like to say that it's not dangerous as there is no option but to follow at distances that reduce drag considerably :) Now I don't know if we have more accidents here than in other parts of the country (I suspect we do)...

I like the big Fed Ex trucks that go way low to the ground. Those are the only ones I find usefull for any drafting purposes. I feel it at about 50' at about 60mph. At 80mph i'll be about 100' and still feel the effect. I only do this if im on the interstate and in a hurry.

The drafting effect isn't as good as slowing down. So I mostly just drive slow and let everyone pass me.