Mythbusters Drafting episode

[Dance_Business]

WARNING DO NOT TRY THIS!!!!!
Drafting a semi truck increased fuel economy by as much as 39%
100 ft = 11%
50 ft = 20%
20 ft = 27%
10 ft = 39%
2 ft = 28%*

* the difference at 2 ft was accountable to feathering the throttle to maintain the distance.
Pretty crazy!

[mr2slow4you]

I think your numbers are off a little? I thought at 10 ft it was like 44% and 20ft was like 41%

[Dance_Business]

That was mpg. Here's the link to the extra footage, web only. A bicycle drafting the truck... I drafted (when I was 16 and STUPID) a truck from Gastonia to Charlotte at about 80mph, my car was in neutral about 1/3 of the time... I knew this one worked. Don't ask how close, as previously stated: I was 16 and STUPID!

[Weasy2k]

wow i knew it did something but that much!

[PETC]

I try to draft as much as possible. I never need to get anywhere too quickly and it works really well.

[Tommy1223]

but then you get rock chips. I'd rather pay for more gas than get rock chips.

[PHOENIX]

someone please explain drafting

[mr2slow4you]

When driving, you are in a huge chunk of mass. Thus chunk of mass has opposition to its inertia, air resistance. Since we are not in outer-space out environment of air is comprised of different gases which have a density. It requires more and more force to overcome these particles.

In drafting, you have an object that is not connected to you that is breaking the air for you. Imagine putting your hand outside the car when your driving, not doubt you can tell a difference between your hand fully vertical, creating a wall, and fully vertical, creating a narrow plane. Now imagine taking your hand fully horizontal, creating the wall, and place your other hand behind it. You would have to provide some force to keep your first, horizontal hand, stationary. But, you wouldn't need to apply nearly as much force to the second hand, since the first hand is disrupting the air flow and breaking it up before it reaches the second hand.

I just got up, so I will re-read this when I am more awake

[PHOENIX]

oh

So in english, if you drive behind a semi truck really close, you get better gas mileage because your not having any air to push through with your car.

[mr2slow4you]

Ya, that sounds pretty good. Not necessarly zero air, but substantially less.

I wonder if the radiator will get enough air flow for extended amounts of time of doing this though.

[mopwer]

Originally Posted by mr2slow4you

Ya, that sounds pretty good. Not necessarly zero air, but substantially less.

I wonder if the radiator will get enough air flow for extended amounts of time of doing this though.

The car doesn't have to work as hard so it doesn't need as much cooling.

This tends to piss off truck drivers since you have to get soo close. Plus if they have to stop suddenly, you're looking for a new car...

Greg

[Davis]

Or a new head...

I'm scared to drive behind trucks! That bar that hangs in the back is scary!

[mopwer]

Originally Posted by Davis

Or a new head...

True...

[PETC]

I won't do it too close, or do it if they don't have full size rock guards.

[RickyB]

I watched part of that show and it struck me as odd that the concept of drafting would be treated as "myth" when it is built on very solid principles of physics and applied in many real-life situations.

Anybody who has done any bicycle racing or has watched pro bike road racing understands the concept of drafting and why the race always has a main group (the "peleton") which is basically a bunch of riders taking turns at the front where they expend maximum effort fighting air resistance and then taking time inside the group where they can cruise along at the same speed while expending substantially less energy. The peleton has physics on its side and a group of riders who work together in this fashion taking turns at the front can always catch a lone rider or a small group of riders who try to break away from the pack too far from the finish.

The same is true of migrating birds who make V formations. The lead bird works hardest and the rest go at the same speed expending less effort. Similar formations were used by bomber squadrons in WW2 to conserve fuel and extend their range. The smaller fighter escorts in particular would ride just behind the bomber's wings saving their precious fuel for their defensive role.

Drafting is very common in car racing where a car can use a leading car to build up speed and slingshot itself past the leading car.

What was interesting about the testing they did was that even at safe following distances of 75-100ft that as much as a 20% improvement can be expected. The only time I have done this is when I was moving and I drove behind the moving truck we rented to haul my furniture. Even though I followed the truck at a safe distance, I constantly stayed behind it for nearly 400 miles and I got the best highway mileage on that trip that I ever managed to get out of the car I had at the time.

If you don't mind the extra rock chips and the slower uphill speeds, following a truck at the safe distance is a great way to stretch your fuel tank. Just use the old trick of waiting for the back of the truck to clear a mark on the road and then have time to count one-thousand-one, one-thousand-two before your front end reaches the same mark.

[Gairloch]

Originally Posted by mr2slow4you

Ya, that sounds pretty good. Not necessarly zero air, but substantially less.

I wonder if the radiator will get enough air flow for extended amounts of time of doing this though.

I'm pretty sure it's not less air or we'd be hearing all kinds of warnings about don't draft on highways with the family wagon or your babies will die of SIDs or something like that. It's that the air is disturbed and easier to move through.

[Hellstorm]

Hahahaha.... thats funny...i thought i was the only idiot out there that drafted behind semi's. Im a contract mechanic for UPS and i get sent all over east Tx to work at different centers. Sometimes i have to drive about 5 hours....so i find a good big Truck....set the cruise control to his speed and get up about 15ft from the back of him......sometimes they dont even know ur there....and other times they get pissed and keep switching lanes to get you from behind them.

[mopwer]

Originally Posted by RickyB

I watched part of that show and it struck me as odd that the concept of drafting would be treated as "myth" when it is built on very solid principles of physics and applied in many real-life situations.

They're running out of real Myths...

Greg

[mr2man]

Interesting

[TheAmazingDave]

Originally Posted by mopwer

They're running out of real Myths...

Greg

They didn't test the concept of drafting as the myth. What they tested was if drafting could yeild substantial fuel savings.