I am still waiting to get my Yaris Hatchback, then I will get a scangauge. If I had my ride and my scangauge I would do this test myself.
Has anyone tried drafting a truck on the highway to see how much it improved their gas mileage? How close to the truck did you need to get?
Roadrunner

Unfortunately, the closer the better, but more dangerous. A study was done recently that showed that the bumper-bar on most trailers is insufficent, and is just the right height to slice your head off in a rear-end collision.

There's a safer "side-draft" technique that's still in the DOT's "No-Zone" as well -- position the vehicle in the lane next to the semi at about where the trailer attaches. This is a bad spot too because it will certainly irritate the truck driver and/or may merge into you.

The best way is the "ACME" claw arm, or the more expensive LECTRO-magnet system (worse for FE, I've found -- take a lot of juice to power up that bad boy).

RH77

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drafting behind a truck is for the suicidal, it isn't worth it to save a bit of gas, i hope no one here does this or promotes the idea.

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I heard long distance drafting (around 1 second behind) still has some advantages. It still is dangerous but not as bad as being 5' behind.

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2008 EPA adjusted:


Distance traveled by bicycle in 2007= 1,830ish miles
Average commute speed=25mph (yes, that's in a car)

You can benefit from 2 to 3 seconds behind trucks and in the lanes to either side of them and the more trucks form in front of you in a convoy fashion and the faster they go i.e. 70mph the more they knock down the wind in front of you and the further behind them it extends so you can safely follow in their wake. Unfortunately you have to breath the exhost fumes and in rainy conditions the dirt they throw up in the mist they create. As far as safety is concerned they usually don't stop suddenly so in that respect they are safe to follow but you need to make sure you allow them room to change lanes should they need to. Getting too close to them is also a great way to add holes to your front paint job and windshield as they do tend to kick up road junk and rocks. Jeeps and pickup trucks are the only vehicles which throw more rocks with their rear tires than semi's because they usually don't have any mud flaps and are jacked up pretty high exposing the rear tread. The first chips in my new xB windshield was from a pickup truck passing me and changing lanes in front of me too close on an empty highway.

Drafting isn't safe and the truck drivers hate it. You'll know when they ride the outer line to kick trash/rocks up on your car. (I sometimes drive a truck for work as a last resort if they can't get anyone else-CDL)

That being said, I have done it at a fairly safe distance at around 65MPH in a 70 zone and gotten 42 with my Matrix when I normal got 37 on the same route. Even at a safe distance its still white knuckle driving that I don't find relaxing. I seldom do it anymore EXCEPT when the beer trucks pull out in front of me in the morning when I'm going to work. The trailers are MUCH more low profile and cut through the air making a great clear path AND remember, they cut in front of me which makes it OK to tailgate - not - its still not right to draft whether I do it or not ( ).

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'08 Smart Passion - GREEN!
'93 Toyota Paseo
'91 Mercury Tracer
'86 VW Jetta Diesel

I kid you not, 20 miles on the odometer of the TSX and a ratty old gravel truck merges onto the highway, hits a bump, and sends gravel flying. Now, I have scratches down to the primer on the hood and dimples in the bumper

I know you can't keep a car new forever, but c'mon!!!

No license plate on the truck, and we weren't getting any closer to get the hauler name. A little touch-up paint helped, but

RH77

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OK, now it's personal. Born in Barberton, Ohio, Alma Mater: Muskingum College, New Concord, Ohio. Folks live in Ohio.

Yeah, come to think, I don't like it there either, that's why I moved away...

Nevermind...

RH77

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I always wanted to make a little grapple for the lower bar on the truck trailer...for my long trips it seems like a money saving opportunity

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Current Stable
GasSaver: 2000 Honda Insight Silverstone w/AC 65+mpg
Track Terror: 2002 Honda S2000 Gran Prix White- lots of mods - 28mpg
Beater: 1988 Honda Civic DX Hatback - Stripped - 30mpg

RIP: 1996 Honda Civic LX 42mpg - you will be missed

http://tomauto.smugmug.com/Cars

...And it's technically carpooling

RH77

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I don't draft either, and after 78,000 miles of hypermiling still have a nice front clip finish.

Rocks/gravel is one thing but if something like a pipe or muffler is picked up off the road can easily kill if tossed through the windscreen.
At least you'll have a chance with reasonable reaction time.

With that said I've had some benefit deflecting a headwind by following a couple hundred feet behind one of those double-trailer FedEx trucks or covered wagons before. Many trucks in a brutal head wind will be going slower but I don't do that much either.

in most cases I'd have to burn off extra fuel to catch up/match speed with a truck and seems to be counter-productive anyway.
99.9% of my truck use is when it's lumbering slowly down the road...in which case I'm blessed with an easy drive just plodding down the road at a safe distance.

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2004 Civic Hybrid AT (CVT)
Personal record: 1003Miles on single tank, 74.9MPG calculated.
Supporter of http://www.fairtax.org

What gets me is I follow at a safe distance and then someone cuts between me and the truck and pushes me back more . . . but as far as safe distance I am further back than most others on the highway.

I dont dragt semis anymore.

In the past it could be good for a 2 to 4 mpg increase when done right. You can also surf the wake infront of a semi.

I took a rock or a kitchen sink yesterday off a Blazer that passed me. It was a ratty, muddy country road rig. I heard a slight wack. And i mean slight. Sound like a rock bounced off under the car. Got to work and found a dent with scratch in it on the leading edge of my hood.

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09 HCHII, w/Navi
07 Mazda3 S Touring, 5MT
Mild Hypermiler or Mad Man?

I think we've all drafted a semi atelast once in our life, in my car when I first got it (shot ignition wire's, original distributor and cap with +100k miles, plugged exhaust (catalytic converter blown out, but stuck in the pipes still), completely fouled spark plugs, bad TPS sensor, bad AIT sensor) It was very low on power, and i had to go to a town not too far away to get some stuff. It ended up being a VERY windy day, i realized just how windy it was when a semi passed me while i had it too the floor going up a small hill, at about 45 mph. I ended up being able to keep up with him, so i kept my bumper stuck to his the entire way there afraid i woudlnt' make it otherwise.

I've noticed the sound of the wind really goes away when your drafting too.

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Actually I never really noticed what difference drafting made until about 5 years ago when I road my motorcycle from FL to TX.

I was on the last leg of the trip (Ft.Worth to Abilene) when the wind picked up A LOT. I was barely able to maintain control. I finally had a semi with a double trailer pass me so I locked in behind him - he maintained 55MPH max. The wind was incredible. He knew I I was behind him and smiled and waved when passed him and took my left exit - he really saved my butt but I am really thankful he didn't kick up a gator or something else.

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'08 Smart Passion - GREEN!
'93 Toyota Paseo
'91 Mercury Tracer
'86 VW Jetta Diesel

Yeah I used to occasionally draft trucks, untill the day my mom came home with a nasty dent/scratch on her hood, from a chunk of tire coming off a semi and flying into the hood. And she was well behind it. Sometimes I just cant help it, because the douchebag semi drivers around here cut people off like its nothing; the other day somebody got killed by one who ran a red light I swear even if a soccer mom was late for work/practice, they would be a better driver than the guys that are getting paid by the mile. I think they should make all semi drivers earn money by the hour; theres such a huge difference in their driving its unbelievable.

If semi drivers would get payed by the hour...they would watch their favorite movies at truck stops.

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Current Stable
GasSaver: 2000 Honda Insight Silverstone w/AC 65+mpg
Track Terror: 2002 Honda S2000 Gran Prix White- lots of mods - 28mpg
Beater: 1988 Honda Civic DX Hatback - Stripped - 30mpg

RIP: 1996 Honda Civic LX 42mpg - you will be missed

http://tomauto.smugmug.com/Cars

I agree with your statement. When I see semi drivers going way too fast, I say to myself, "he is getting paid by the mile, not the hour". If they all were paid by the hour, as I am while driving, they would go a more reasonable speed IMO.

Roadrunner

Just another mpg result for this thread. The SG in my Geo was reading 37.5mpg average when drafting a truck (about 2-3 seconds behind) @ 70mph with cruise on (temperature 27*F with no wind). I changed lanes with the same speed and the average was 36.3mpg. That's 3.3% increase, but it's still nothing compared to driving @ 50mph (returned 49.8mpg).

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ahh yes motorcycles, i was commuting on mine one day when i came upon a large semi, i got up behind it and was just starting to enjoy the quiet and smooth ness when he decides to tell me he doesnt like me. In to the gravel he goes i become momentarily paralyzed by the fact that my helmet was filling with dust as my body was being pelted by stones (no fairing, screen, or anything) NOT GOOD, so then i passed him only to find semi's are long, my motorcycles' not fast, and there was oncoming coming fast :-(

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In the UK, trucks (lorries) are speed limited to 56mph by law, and most of the limiters are actually set to 53mph to ensure they don't break the speed limit (this is based on GPS results). You can drive 2 seconds behind one of these, and if you put your hand slightly out of the window, you will feel a lot less wind when driving this far behind, compared to driving with an open road. Driving closer than 2 seconds gives better results, but is a bit dangerous, so I don't do it. Also, when it is raining, it is too difficult to follow them due to water spray.

I can imagine, if the lorries did 70 (as they did when I visited the US), it would be a lot more dangerous to draft them, and more economical to drive at 50 anyway, but in the UK I get the best of both world (lower speeds + drafting capability)!

I *always* draft trucks in the UK - they go a lot more slowly, never throw anything up, and 2 seconds is a bigger distance than most people leave anyway!.

By the way, I have found that driving alongside trucks/lorries is actually bad,
because the lorry pushes the wind aside, and you get an extra-dense faster moving column of air hitting your car - when a lorry goes to overtake, you can feel a sudden decrease in speed as the wind hits you.

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Team GasMisers5 - #1 for first three rounds of the original GS Fuel Economy Challenge
Miles displaced by e-bike since 1 Jan 2008: 62.6 (0 kWh used)
Hypomiler