Drafting with scangauge
 

had a chance today to draft a semi while using a scangauge. driving my wife's car(my car is not SGII compatible)gave me this opportunity. VERY interesting.

70mph avg ~29mpg no drafting. when drafting(i'm a truck driver, so i did so w/ mirror in view) again @ 70mph avg ~35mpg.

now, this is where it gets interesting. drafting, same speed, downhill(slight decline--not very hilly here), yeilded a high of 182mpg. WOW!

Cool.
Thanks for the "hard numbers"!

I do draft sometimes when a good opportunity presents itself. I like drafting box trucks and buses; their back end goes lower to the ground than semis. I make sure to not get too close.

The tough part is, it usually requires some pedal work to stay appropriately close to draft the truck ahead. I make an effort to avoid going so fast that I end up with a reduced net mpg.

Hills - yeah. Once today I had to brake on a downhill because I was getting too close to the draftee up ahead.

bowtieguy -

Yeah, downhill is VERY rewarding MPG wise. My imaginary perfect MPG freeway would have a Ferris Wheel scaled for cars on each end. You would get on the Ferris wheel, be rotated to the top, and would *always* be going downhill (if even only a gentle slope) the whole way. The other end of the freeway would have a Ferris Wheel for the opposite direction.

CarloSW2

If you're going downhill you might consider an EONG (Engine OFF in neutral glide), that's technically unlimited mpg. I usually do this when I foresee at least 1/4 mile without the need for engine power, generally speaking a good 15-20 seconds or more, big long hills.

Please don't get too close, I HATE these people like to ride up the bumper of my trailer.
What I do then is I go EONG until it forces them to pass, I'll come to a complete stop if it came down to it.
I don't have too much an issue with folks who back off after they find themselves in it, that's one thing but it's usually some family car just plasters themselves there and won't increase their distance...

You know it's about safety, I understand it's their fault if they hit me, but please understand that if they DO hit me then it also wastes at least 2 hours of my time, that's not even counting all the bs comes after we're out of there.

Oh and not-at-fault still raises my insurance:
Policy activity increases premium.

I had my first chance to compare drafting and not drafting on a long trip. Drafting yielded a solid 2mpg increase...which for me is significant as that is close to a 10% increase. I did notice that if I found a bus I could be further behind it and still get the drafting benefits. 28+ mpg avg for 700 miles on a car with an EPA of 23mpg-hwy rating!

Got 36mpg in Marvin drafting all the way on a long haul. It's hard to do sometimes though, gotta find a truck just going steady.

Even harder to find a truck which slows just the right amount going up hill, so you can bleed off some of your speed. Of course, when you do catch a good one, your wife will need to get off at the next exit anyway. :)

I have found you can space your self back about 2.5 seconds and still get the benefits of drafting. Do not do this at night or in the rain or bad weather.
The down side is you must keep all your attention on the truck ahead of you.
If you have never done this you soon find out how mentally tiring it can be even after 20 to 30 minutes. Second your front end will take the blunt of all road debris that the rear tires on the truck or bus ahead of you kicks up off the road.

Yup, you don't need to be right on the truck's bumper, the draft (vacuum rather) has effect out to about 3 lengths of the vehicle making it at highway speed. So therefore you can give most bigs semis a good 100ft. Bear in mind this also means that shorter vehicles won't give such a good safety space. Look out for lightly loaded and empty trucks, they'll generally be bouncing a lot on their springs. Their stopping distances are significantly better than laden trucks, so you have to be extra careful. Typically a large and laden semi should have a stopping distance in the range of 2-3 times that of a typical car. However, if you have put on thinner than stock, hard compound tires, at high pressure, your stopping distance might be longer than stock. Often you can see brake light shine of vehicles in front underneath the truck, don't rely on this, but extra clues like that may help you drive better.

Do not draft flatbed trucks even if they have a large covered load on. Their beds get a heck of a lot of debris and detritus built up on them from construction sites etc, huge hard clumps of mud, gravel and grit, get close behind one of these suckers for long and you'll get stoned to death.

I don't doubt it for a second. But a question. Didn't the truck driver not like you drafting? I stopped drafting because I got varying levels of messages to "get off my tale" One truck driver even hit the brakes pretty hard. Another one put on bright white lights on the back of his truck. So I've taken the hint and stopped doing it. But I'm wondering maybe it was because I was not in their rear view? Doesn't it slow them down to drag on them (aren't they essentially pulling you when you draft Going down a hill on the Mass Pike (I-90 headed toward Boston) there is a 6 mile hill that goes into the Pioneer Valley. In a prius, you can actually charge the battery going down this hill drafting! Driving a friend's Prius, drafting behind a truck down that hill, I got the battery completely charged.