drafting semi's
 

okay, first off I know it is dangerous...

I recently discovered that you can be 50 to 100 ft back and still see a benefit?

I heard mythbusters found a pretty significant increase all the way back to 100ft?
Or did i hear wrong?

I am pretty confident that i can still be safe at 50-100 ft back, and was wondering if anyone with scangauges have done any informal tests with this?

In the past I've drafted within 10-15 ft off semi's with little problem.
However, i dont drive with that kind of risk level anymore...

but 100 ft is quite safe in my opinion

thoughts?

Well, 65-70 feet or so is about 1 of their length. Too close for me. I like to be 3 of their lengths behind and no more than 55 mph. I love slow trucks!

PS Yes, I use the scanguage to confirm this - AND it depends on wind speed and direction. Side winds - forget it. Head winds - nice benefit.

okay, so a full semi truck length back you are seeing an increase?

i understand about the side winds...been there done that

so 65-70 ft back, what kind of increase are we talking here?

I can get roughly 10-20% from drafting. Over 55 mph the benefits decrease. In my little car, I can feel the difference like night and day. I get back a little too far and I have to stay squarely behind him to stay in the draft. A little to the left or right can throw me back out of the envelope. I get way too far behind and I can feel the buffeting which tells me I am out of the envelope, plus the scangauge confirms this. After 65 mph, I give up and fall back to my grandpa driving. This is just my informal findings.

wow, well 10-20% is a lot.
Damn, I need to bite the bullet and buy a scangauge...with xmas time here, we have been spending and spending and spending, lol

I hate to sound like I'm beating a dead horse...but WHY do you think over 55 there is a decrease in benefit? If find most of the semi's in my area are doing 65 or so....
And how far, that you have found personally, is usually too far away? A full truck length? Less or more?

I will get a scangauge soon, and try and do some testing and report what I find.

I'm just so intrigued as I thought I would never draft again until I found that you can do it from so far away. To me, this is a safe enough distance...100ft that is...

So I saw this gasoline tanker and decided to give chase....

Last time I drove down the highway in the rain, I observed the spray in the air comming off the back of a semi in front of me.

I'm guessing it must be a rough indicator of the proportions of the hole they punch through the atmosphere and may give an idea of where the sweet spot is for drafting in other conditions. (Although I suspect the weight of the water vapor would tend to show a smaller clear pocket than in dry conditions.)

I drafted behind a Greyhound bus on a motorcycle once. The turbulence was like getting between two guys boxing each other wearing pillows for gloves. It was on one of those California 12 lane freeways with heavy traffic.

I did not save any gas, and got beat up in the process.

Over 55 the benefit of the cleaner air is overcome by all the other factors of increased speed.

I'm a big fan of minimum safe following distances. Two seconds is good three is better. The faster the truck is going the further back you should follow. 65-75 feet at 55 is way closer than what is safe. At 65+ that distance is plain stupid. I don't like people riding my butt, why would I do it to others?

Kirk

I agree. Safety is more important to me than miniscule increases in fuel economy.