drafting semi's

[mattbatson]

i think people should drive within their limits and the limits of their car.

A good man knows his limitations.

[PaleMelanesian]

This controlled study shows clearly that drafting has a benefit to both vehicles. The 2nd gains more, but the leader still gains something.
Reducing Aerodynamic Drag and Fuel Consumption (warning, PDF)

That said, I don't consider drafting a valuable or safe technique. Too many bad things can happen too quickly.

[mattbatson]

Originally Posted by PaleMelanesian

This controlled study shows clearly that drafting has a benefit to both vehicles. The 2nd gains more, but the leader still gains something.
Reducing Aerodynamic Drag and Fuel Consumption (warning, PDF)

That said, I don't consider drafting a valuable or safe technique. Too many bad things can happen too quickly.

regardless of this fact, I have a very hard time believing that my little civic sitting 60 ft back from a semi will have any significant effect on it's FE....

thx for the link

[user removed]

Anything that fills a portion of the low pressure area behind the host vehicle will improve it's mileage. To better understand this imagine completely filling the low pressure area with an object that would provide the perfect shape to eliminate the low pressure area altogether.

That's the perfect boat tail.

regards
Mech

[sheepdog 44]

During my 10 mile non highway commute, drafting has become non advantageous. I accelerate reasonably slower than normal traffic, And let the "pack" flow past me as i keep the optimal speed for the given speed limit. I'd end up using more gas accelerating into position.

The only problem is a certain section of lights stay green for the traffic pack and if i drift too far back i end up hitting red. I like my buffer zone. If there are unexpected reds around a corner i have plenty of room to drift and maintain speed when it changes.

Be safe people!

[Patrick]

On a recent vacation I had the opportunity to draft a semi at 75-80 mph for several miles in my 2010 Prius. As you can see (hopefully) from the pictures, I was averaging over 100 mpg for at least 20 minutes. The wider bars in the graph at the right of the display are each 5 minute averages and go up to the 100 mpg level. I was keeping about a 1 second following distance and had no problem reacting to changes by the semi driver. This was in southeastern Wyoming and I was following a North American Van Lines semi. Mileage in free air at the same speed was about 40.

[ksa8907]

i see between 20 and 40% increase depending on the type of trailer, current wind conditions, and following distance.

from what i have experienced, less than 50ft gives amazing mileage (i only did it to test), but is absolutely not suggested. 50-75ft gave me a lot of buffeting and didn't help much. 75-100ft gave the most stable airflow and the best of safety, comfort, and mileage.

[serialk11r]

Funny how you guys are talking about 50ft as if it's really close...over here in California if you leave 50ft between you and the next guy there will be 2 people trying to squeeze into that gap. Yes, I'm talking about at 65mph.

When people switch lanes after riding my tail I can usually feel the drag increase, and I can feel the drag difference when someone merges in front of me too. Common experience is to be tailgated on the highway and see my speed go up without moving my foot.

[ecomodded]

On the highways i find a slow traveling large truck or RV and tuck in behind them,without being a tailgater. More often then not the trucks speed starts increasing and i back off and drive my preferred gas saving 55-60 mph.

[serialk11r]

Originally Posted by ecomodded

On the highways i find a slow traveling large truck or RV and tuck in behind them,without being a tailgater. More often then not the trucks speed starts increasing and i back off and drive my preferred gas saving 55-60 mph.

That's the preferred situation of course. I was getting almost 50mpg following this guy in a dodge truck pulling a rather large trailer thingy along the right lane at 55mph, and it was relaxed driving for me too. 50mpg is astounding for my gearing, which spins the engine at 3000rpm to go 55mph. With no cars to draft I max out at about 55mpg going ~35 mph steady state cruise (though this is going off Torque, which sometimes is giving very obviously inaccurate readouts).

Otherwise, I try to draft faster moving large vehicles for as long as possible without speeding up too much. Saving some time isn't too shabby of a proposition. Average speed of 65 drops the fuel economy to high 30s, but if I can draft at a pretty big distance even it goes up to about 40mpg.