dz302

I have been practicing many techniques for about one year to improve mpg in my xB. The one I had never done was drafting. This was primarily because of what I considered safety issues which may be of concern. However, on my recent trip to Florida I decided to give it a try. I have a scangauge for monitoring efficiency on the fly and the highways in Florida are all but slate top flat.

At a steady 65 mph with cruise control set I watched the instant MPG flutcuate between 32 - 40 mpg and usually settled into around 36-37 mpg as the cruise maintained a constant speed. I traveled like this for about 20 miles.

Then I allowed an 18 wheeler to pass and I tucked in behind him. My guess would be 5 - 7 car lengths. He was traveling about 70 mpg so I figured my mileage would go down. However, after approx. 20 miles my scangauge fluctuated between a low of 38 and a high of 55, usually settling in the 44-45 mpg figure.

As for my AVG MPG: Starting with a full tank of fuel, the first 100 miles or so of my trip were all 55 mph state highways until I hit the Interstate. My AVG MPG had settled in at about 42 MPG and had leveled off. Once I got onto the Interstate and settled into a 65 mph cruise I watched as my AVG MPG slowly deteriorate to and settle at about 38.5 It stayed there about 30 - 40 miles. After my 20 miles of drafting the big truck it had climbed back up to 39.9. At this point, the truck exited the highway and I never got a good shot at it again before running into a widespread rain storm along with high winds. Experiment over. I know the 1.9 MPG improvement doesn't seem like much but keep in mind, it was only for 20 miles PLUS as you get deeper into a tank of fuel the more slowly the AVG MPG will go up or down. PLUS my speed when drafting was right at 70 mph versus my previous 65 mph when not drafting.

I firmly believe that I could have averaged somewhere around 50 MPG if I could have drafted a big truck at 65 MPH. Not bad. I'm hoping to get a longer experiment on my way back home. I would love to get a good 100 miles or so as an experiment.

I know there are issues with drafting such as following too closely and avoiding flying debris. I believe I could easily out brake a large truck (I was paying very close attention while drafting). As for debris, I ride a bike too and flying debris is always a concern.

I would like to see other stories about drafting experiences from those who have tried it.

Thanks.

Jim

P.S. NO FLAME JOBS ABOUT FOLLOWING TOO CLOSELY. JUST LOOKING FOR SOME SIMILAR EXPERIENCES.

WhoKilledTheJAMs

Please be careful and don't do anything stupid.

Truckers don't like being drafted, because they can't tell you're there. Yes, you can out brake them, but if they blow a 150psi tire, it could really ruin your day. Not super likely on any given day, but given how many truck tire carcasses I see on I90, I can't imagine it's that unusual an occurrence.

As much a fan of hypermiling as I am, I have to recommend against much drafting.

On the other hand, I get really good results when people draft me for long distances on the interstate. It's counter intuitive, but it does benefit both vehicles from a strictly aerodynamic standpoint.

Sciond

dangerous yes...works yes...

InfiniteVisi0n

Drafting is good if your racing other than that it doesnt save you money. You have to be extremely close in order for it too work unless its a huge 18 wheeler. But if you think about it, you might save money on better mpg but in the long run..all the rock chips and stuff that would be rocketed to your front bumper wouldnt help your wallet...considering that you want to have a nice ride.

ZOMGXB

I, too, tried drafting on a trip to Florida (from Chicago), and even maintaining a safe distance I averaged 37 MPG for the entire trip. Probably saved me $200.

Actually, Mythbusters demonstrated that the optimal drafting distance (behind a semi) is 50-100 feet. In fact, it's often possible to still observe the "2-second rule" while drafting.

I had my passenger take some pictures while I was drafting, to prove it was a safe distance. Not only was I in an adequate stopping range, the people in the lanes to my left and my right were two to three times closer to the cars in front of them. That's standard, in fact, around these parts. If you allow any more distance you get tailgated, and then cut off.

however: In my experience, drafting is really only useful for long trips, and not at ALL useful if there aren't many cars on the road (if it's just you and the semi, you'll just annoy the crap out of them). But for long overland trips: all the cool kids are doing it.

Question for the group: the purpose of driving to Daytona was to pick up my boyfriend, who then followed me back north in his Mitsubishi Lancer. The Mitsu has a slightly bigger engine and usually uses more gas, and yet for 1300 miles we were putting exactly the same amount in every time we filled up. He followed me, and was 4-5 car lengths back the entire time...is it possible he was drafting off of MY BOX? o_0

InfiniteVisi0n

you have a boyfriend?

WhoKilledTheJAMs

Actually, yes. You don't have to tailgate to get at least some benefit from drafting. Plus, I'd bet that you were driving a sensible speed, which helps a lot too.

InfiniteVisi0n

^^how come in nascar the driver has to get so dang close to each other?

WhoKilledTheJAMs

Because drafting does work extremely well at close distances. This is one of the few things that was actually thoroughly tested on Mythbusters. Basically, the closer you can get while maintaining your speed with minimal effort, the better. There's a point, however, where you're so close to the vehicle in front of you that it's so difficult to concentrate on not hitting that vehicle that your mpg suffers due to throttle and brake adjustments.

In NASCAR races, the cars are essentially all identical, and extremely predictable. I'd imagine that removes some variables in terms of how fast one can draft at a given speed. Plus, they aren't doing it for efficiency-- what makes drafting efficient is that driving in the low-pressure area behind a vehicle literally drags yours along for the ride too.

InfiniteVisi0n

wanna drive down to chicago so I can draft behind you?

mrfuzzy4

As long as you're safe about it then i dont see why not. I do it to big trucks zipping in the fast lane. as long as you give them a good bit a room, you'll still get some draft and thus better milage. also try "cruise control", or keeping a constant speed, or better yet, try 50-65 mph. optimum speed.

but hey, if you can get that many miles, it will pay for a long trip.

VIP_CAMO

this was done on mythbusters...

ZOMGXB

That's really the most significant thing you picked up out of my post?

As it happens: he's more like my fiancee. Turns out they're letting ___ people on the internet now! What'll they think of next. Is that a problem, junior?

You're really not helping the stereotypes associated with tC drivers.

ZOMGXB

I sure was, since he was following, and I didn't want to lose him in, say, Murfreesboro, TN.

I just didn't think our box had the mass to act as a windbreak.

WhoKilledTheJAMs

OMG what's next, cats marrying dogs???!!111

Seriously, though, that post sorta irritated me, too, but since it's not my personal beef, I didn't want to be the first to say something.

/not ___, just a sensible, progressive human being

Btw, the box is one heck of a windbreak, because of the vertical rear end. I like when people draft me for long distances. If you're paying attention, you can tell, because you don't have to apply as much pressure on the gas pedal when someone's behind you, or vice versa.

ShadeOfBlue

Drafting can work both ways, for the guy in front and the guy in back. It is also called slipstreaming when you use the term in that way.

Basically, every vehicle has air resistance in front, where it is disturbing the air, and behind it, where the air must come back together after the vehicle passes. Both areas cause air friction and thus drag. And naturally semi trucks and xBs do encounter this especially so due to their non-aerodynamic profiles.

When two vehicles draft/slipstream, it helps eliminate the drag behind the first one, and the friction on the front of the second one. In the extreme case of race cars, it's almost making the profile of two cars closer to that of one long car (but with 2 engines, so you come out ahead).

Even with some distance between cars you can see some benefit, because some of the air in between the two does not need to move, and can act as a buffer that results in less turbulence. The Mythbusters showed a similar concept when they showed that a pickup truck can act as if it was more aerodynamic than it is due to the pocket of air that sits in its bed.

All that being said, if you get too close, you lose MPG due to speed adjustments, and the more you micromanage distance and speed, the less you can focus on safety and awareness and of course enjoying your trip. And safety should trump all of these concerns; a crashed car gets zero miles per gallon.

dz302

Drafted for about 20 miles on the return trip and the mileage was averaging 47 mpg on the Scangauge. Then I quit drafting and the average settled into 39. Both times my speed was just under 70 mph.

On the next tank I settled into a 65 mph cruise and got 41 mpg on the tank.

Drafting was a good experiment, but I'm done. 41 mpg is great and I can live with 65 mph. I'm never in a rush.

Zombietime

Oh is that why so many pickup truck and suv and pontiac grand prix _______s tail gate me? They're drafting like the redneck nascar tards do. I just think they're dicks but that's just me.

dz302

Hadn't figured that one out yet huh?

bB2NER

That and sandblasting your front end and windshield. Then there is the occasional road gator that might get kicked up. Some states also ticket people that follow big trucks too closely.
I avoid big trucks like the plague. A few extra mpgs are not worth the damages.