Drafting Tractor Trailers for mpg gains.

[mechtech2]

When Nascar drivers drift, it helps the rear car the most, but also helps the lead car.
Similar results should be for a car and a big rig, with less help for the truck.
If the truck driver is not a personal friend, he may get touchy about you hanging on his arse.

 

[CLG]

You could load a car inside of the TT and not notice any difference certainly not gonna feel him behind you it is a safety issue and that is why it bothers us.

 

[gedcruise]

Find a rig carrying new Hondas. Draft it to whatever dealership it is going to. Go inside, and buy a new five spd Accord, Civic, or Fit.
Viola!. You will most likely enjoy improved fuel economy for years to come.
So, drafting can work, if done properly.

 

[g20ooh]

Not quite the exact topic - but possibly useful .



http://www.greencarcongress.com/2007/07/platooning-redu.html


" - They found that the platooning of vehicles at close spacing reduces the drag coefficients of all platoon members, regardless of the vehicle’s shape. The higher the number of vehicles in the platoon, the lower the drag coefficient. -"


" - The leading car in the platoon experiences the highest drag as you would expect but no more than if it were driving alone.

The second car has a much lower drag coefficient than the first car in a two-car platoon.

The middle car experiences the lowest drag in a three-car platoon

and the third car in the platoon, starting from the front, experiences the least drag in a four-car platoon. -"

—Debojyoti Mitra


Drag coefficients (CD) in a four-vehicle platoon


Car platoon (4) /// Bus platoon (4)


Vehicle 1. 0.331 /// 0.868


Vehicle 2. 0.273 /// 0.602


Vehicle 3. 0.225 /// 0.424


Vehicle 4. 0.284 /// 0.521

 

[g20ooh]

Here is a great example of optimising the effect .


http://www.caranddriver.com/reviews/3237...ating-much.html


ROAD TEST: How We Won the Insight Fuel-Economy Challenge. Without Cheating. Much.


By DON SCHROEDER, January 2000

Honda proposed a contest: Which automotive magazine could get the best fuel economy from the new Insight in a 195-mile run from Columbus, Ohio, to Detroit, combined with the mileage achieved in a four-lap exercise around Honda's 7.5-mile proving ground?

That would be us, of course. Who else?
As for the highway run, we asked Andy Boyd, Honda's Midwest PR maven, if drafting--the racing art of tucking closely behind another vehicle to avoid wind and air resistance--would be legal.

"Drafting is legal," he replied.
"And we can draft any vehicle of our choosing?" we further inquired.

"Any vehicle you want," said Boyd. -"

 

[rpn453]

Nice find, g20ooh!

 

[Matt_S]

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Uh, no. It doesnt work like that.

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So how does it work? Or are you content just to rag on me without knowing the principles at work yourself?

 

[rpn453]

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So how does it work? Or are you content just to rag on me without knowing the principles at work yourself?

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If what you said was true, wouldn't a flat back end be the best aerodynamic shape instead of the worst? Airfoils taper down very gently on the trailing edge to avoid flow separation and the vacuum it creates. Flow separation is never a benefit when it comes to aerodynamic drag.

 

[badtlc]

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Uh, no. It doesnt work like that.

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So how does it work? Or are you content just to rag on me without knowing the principles at work yourself?

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I'm not ragging on anyone. I'm sure you can find the answers w/out too much trouble. I can see why you thought that, but it is not correct.

If you get desperate, watch a nascar race. They have some nuggets of useful information sometimes with regards to aerodynamics.

 

[Black Bart]

I spent 42 years as a long distance trucker. While a tailgating car may affect the airflow it is not anything that you can tell or feel while driving the 18 wheeler
Most truckers don't like to be tailgated and have a way of curing it.
You just slowly drift to the right and allow the outside dual to drop off on the stone.
The blinding dust and barrage of stones will cause them to back off every time.

 

[CLG]

I don't know how legal Drafting is but, tailgating is illegal seriously guys someone will read this get ideas and then go and get themselves killed you have to consider that all types of people will read these kinds of posts and try to out drive there own ability. Commonsense is the most underrated form of intelligence.

 

[Camu Mahubah]

Just got off I-80 from Cheyenne WY to Sydney NE... thought about drafting semi's but since I am not a teenager anymore and the wife was in passenger seat decided against it. Also I was getting approx 38 mpg at 100km/h (62 mph) Yes I went 62 mph from Ft. Collins CO to Sydney NE. Was thinking next time I'll need a car that will run 75mph comfortably. and get at least 30mpg. I know this is

but I wanna make a topic about the best interstate car what section should I put this in?

 

[Palut]

Does one really need to tailgate to benefit from drafting a semi? Those trailers move a huge amount of air and have very poor aerodynamics on the back end.

I figure that if I stay a safe, normal distance behind them, the air I'm hitting will still be disrupted due to the trailer's passage. It's a total guess on my part, but I imagine it's still doing at least 10-20 mph when I hit it, so I gain a little bit. So if I'm doing 65 following a semi at a safe distance, I may have the aerodynamics of a car traveling 45-55 mph.

It's not like true drafting, but a benefit nonetheless.

I'd love to mount an airspeed indicator on my car to find out how effective following other vehicles at different distances truly is.

 

[wantin150]

Just my .02 here. Braking distances on TT's depend alot on load. Obviously, a full load will lengthen the distance but the trailer will make better use of it's brakes where as an unloaded trailer will make very inefficient use of it's brakes. IIRC, the trailer brakes only provide something like 5% of the total braking percentage (each set, so a tandem trailer axle is only 20% total). The scary thing is that when you do the math, even with all brakes (truck included) working properly, the total still isn't 100%.

Next time you come up behind a TT, ease up into the "wake". It's not a pleasant experience!

 

[Junior]

Umm, I can tell you, if you don't have any trailer brakes you are missing much more than 20% of your braking ability.

Assuming a fully loaded truck (12,000lb on the steering, 34,000lb on the drivers and 34,000lb on the trailer) and properly adjusted slack adjusters ideally the trailer should provide 42.5% of the braking, the drivers 42.5% and the steering 15%. In practice is it different but more than 20%.

Also remember that since a semi uses air brakes, the brake lights will be illuminated for about half a second before the truck actually starts to declerate.

 

[brianl703]

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I'd love to mount an airspeed indicator on my car to find out how effective following other vehicles at different distances truly is.

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Voltmeter or frequency counter on one of the engine cooling fans (if electric). Since the electric cooling fans (most cars have two) are turning due to the airflow even if not powered, they should be acting as a generator and producing a voltage and frequency output that increases with the fan speed. Fan speed should be dependent upon air speed.

Of course this won't work if the fan is actually powered, but in that case maybe you could measure the current draw of the fan which should drop as the load on the fan drops. The load on the fan should be inversely proportional to the speed of the air entering it. So the current consumption of the fan should go up as the airspeed in front of the car drops.

 

[eljefino]

Having walked on a shoulder and passed by 18 wheelers I can report there is not only the "big" wind, but, a couple seconds later, a gentler "after-wind". I feel good when I'm the requisite 2.5 seconds following distance, and the car's rocking a little. Figure I'm given a few MPH headwind. Science? None.

 

[Lonnie]

Just put a fan on a stick, attach it to the front bumper high enough to see while driving and see if it slows sown when you get close to a truck. Slow is better.

 

[Gary Allan]

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Does one really need to tailgate to benefit from drafting a semi?

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No, you don't. All of you try this. Just roll down your window. Real noisy. Approach a stable speed semi and just listen. When you're inside the envelope ...it will get quiet. My jeep's flat front isn't being slammed by a wall of air. The edge of this envelope is a decent distance behind the semi. I don't think you need to have the whole vehicle inside that (for lack of a better term) dead air space. Think Millennium.

Naturally, my jeep has a big disadvantage compared to just about anything except a semi..so YMMV. One way on a trip to wester PA ..70-75 17 mpg. Return trip 65-70 taking advantage of various semi's over the 245 miles whenever practical (grabbing a faster semi as they made themselves available - picking up new ones as they left the roadway - 23 mpg.

 

[harry j]

What do you call a car that drafts a semi?


A bumper sticker