• Oct 28th 2007 at 8:13PM
  • 23
Warning: Don't try this! The safest distance to drive behind a big rig at 55 miles per hour is 150 feet. Driving any closer is insane because it puts you in the driver's blind spot and also does not give you enough time to respond if the big rig's driver changes speed. This post is for informational purposes only.

Drafting is a technique, usually used by race cars, to reduce drag by driving closely behind another car. Mythbusters did an episode about Big Rig myths that included a look at the drafting... myth? Does anyone really consider drafting a myth? Anyway, they found drafting increases your miles per gallon up to 39 percent at 10 feet distance away from a big rig. At two feet apart however, they found miles per gallon actually went down.

The first part of debunking the drafting myth took the Mythbusters team to small wind tunnel to prove putting things in front of other things blocks wind. Good thing, too. I know I've always questioned stories of objects blocking the wind and can only be convinced by a wind tunnel experiment. Sarcasm aside, while the episode was dangerous and 39 percent is kinda shocking, Mythbusters should not have done this!

No one thinks drafting is a myth and the information they gathered only encourage people to try this. What's next for Mythbusters; how much will over-inflating your tires increase your mileage? How much fuel can you save by turning off your engine at high speeds? How many engine parts can you remove and still drive your car? Mythbusters did warn that driving so close to a big rig is insane but doing tests that find the drafting sweet spot looks like encouragement to me.

[Source: Mythbusters]


I'm reporting this comment as:

Reported comments and users are reviewed by Autoblog staff 24 hours a day, seven days a week to determine whether they violate Community Guideline. Accounts are penalized for Community Guidelines violations and serious or repeated violations can lead to account termination.


    • 1 Second Ago
  • 23 Comments
      • 7 Years Ago
      Regarding @1: Under the "don't try this at home heading"... Check it out on your car first, but some US cars with slush boxes won't start back up unless that car is in Park. I've stumbled on it one time when my Buick stalled at about 60 mph after pulling onto a freeway on ramp. Turning the key to start did nada. Put the prndl in "N", nada. Not gonna save too much gas that way, but check your car first! That and most cars need the engine running for the power brakes and power steering. Ironically '87 Turbo Regals all have electric power brakes.

      That said, I drop my stick shift into neutral and let out the clutch (saves the throw-out bearing among other things) on EVERY downhill that gets me a positive speed increase. Of course we're not talking 4 mile hills in my commute, but it is rolling for about 25 of the 37 miles. There is only one hill where my car will pick up more than 15 MPH on the downhill. That is one thing that helps me get 29-30 MPG per tank on a car with a 26 MPG HWY pre-2008 EPA sticker. Hey I burned the gas to get up the hill, why not get some of that back going down the hill!

      I'm not sure you'd see TOO many more miles between idle and shutoff and granted EVERYTHING we're taking about in the post is going to be branded reckless or dangerous by Click-n-Clack and probably by your significant other, at least having brakes and steering while coasting would be a good thing.

      Almost forgot.... In the Metro DC area, the most common following distance for a semi doing 55 MPH IS 8 - 10 feet. Of course if you're doing 55MPH on the Beltway, heaven help you, because the semis with be 5 feet from YOUR back bumper.
      • 7 Years Ago
      Where I am from (Detroit), as another user mentioned, drafting is an every day occurrence. While I may be driving with a 50 foot buffer (which, in my opinion, for an experienced driver in a car with decent brakes is a safe distance to follow at), which according to many people would be considered drafting, I will very often get cut off by one OR TWO people! Yeah, as in bumpers being only 3-5 feet away from each other. THAT is unsafe. Following behind a tractor trailer, especially if you use a CB radio to tell them what you are doing first, can be a safe practice. I personally don't do it as habitually, but I don't think that it is nearly as unsafe as everyone makes it out to be. Idiots weaving through traffic at 100 mph are the real threat to other drivers.

      As for why it works, a simple example comes to mind. Think of a Canadian geese flying V. The ones in the back are getting a FREE (or partially discounted) ride. They take turns though, and semis usually don't get such an offer.
      • 3 Years Ago
      " What's next for Mythbusters; how much will over-inflating your tires increase your mileage?" Actually, yes, they DID test effects of overinflated tires on fuel efficiency (episode 153 - Mini Myth Mayhem). They found that overinflating the tires (60 psi vs. 35 psi, which is the manufacturer's recommendation) reduced the fuel consumption of their test vehicle (a sedan) for about 7.6%. They also tested slightly-overinflated tires (40 psi) with the same car, resulting in a 6.2% decrease in fuel consumption. Despite this, they also advised against this technique to reduce fuel consumption, since overinflated tires reduce the available traction on the vehicle, and the fact that the efficiency advantages are minor compared to the risks involved in such a practice.
      • 7 Years Ago
      Tried this last year returning from Florida, averaged over 33mpg with a full sized auto for 1,000 mile road trip. Average speed was approx 70mph. Noted an increase in mileage while drafting per on board display. Found that slowing down also works well, with a several mpg increase in slowing to 60 and 65mph. Be safe!
      • 7 Years Ago
      "Mythbusters should not have done this" Why? Do you think people will now go out and draft big rigs because there is a gas mileage benefit? How about some personal responsibility? If anyone is dumb enougth to try this they should not be driving period.
      Atul
      • 7 Years Ago
      Realistically, in urban driving, how often can you drive at least 150 feet behind a big rig? I would say that average following distance is more like 50-60 feet and in Detroit traffic 30 ft or sometimes less is necessary lest somebody squeezes between you and the truck. That would be more dangerous than being behind a truck. Trucks brake more slowly so you have more time to react. And when there's lots of traffic you have to believe that truck drivers assume a vehicle is behind them at all times.

      Drafting big rigs up close happens all the time. It's not safe, but it's safer than the alternative of being behind a car or SUV that is more likely to make sudden movements. Trucks just can't move as suddenly and their high view of the road allows the drivers to react in advance. They decelerate more slowly, so you're better off. Just don't drive under the truck's trailer and have that bumper bar knock your head off. :-)

      UH2L
      http://www.thingsivenoticed.com
      • 7 Years Ago
      All cars are required to start in P & N. More than likely it is GM's sensor is misaligned. It happened to me once, if you lift up ever so slightly (toward reverse) the sensor lines up and the starts spins.

      You waste gas by putting a stick shift car in Neutral and idling the engine.
      All cars have overrun fuel cutoff.
      • 7 Years Ago
      The trick however, is that it does not actually reduce overall milage. And the reason for that is that the rig in front actually has to work harder to pull the car along behind it. The bubble of air behind the rig gets bigger, increasing drag.

      It's the first rule of thermodynamics. There ain't no free lunch.
      • 2 Years Ago
      Why not just slow down? I drive 30 miles to work (60 round trip) every day using the interstate. Posted speed is 65, most people drive 70. I set my cruise control for 60 and reap the benifits, 10% better fuel economy. Its not easy at first, being among the slowest on the road, I still get passed by big rigs and there not supposed to go faster than 55. I use to drive with the flow of traffic (for safety) but when you cant afford the extra cost of what 5 or 10 mph slower can save well, ya gotta do what ya gotta do to get by. And driving slightly slower is alot safer than drafting that 18 wheeler, especially when one of his rear duals blows out. BOOM!
      • 7 Years Ago
      if you have the instant MPG display in your car you can see this. moving van trailers work the best because they are closer to the ground in the rear than a standard box trailers which allow the air to pass under.
      • 7 Years Ago
      Am a 48 state over the road,(OTR)trucker and I can tell y,ll that anybody who is driving so close behind me that I cant see them,and only know that they are there because of either a shadow or their headlight reflections, is asking for an accident, it causes a great deal of stress to the average truckers that ya,ll have NO idea of how to drive around the biggest trucks in the country safely. basicly stay away from us,we cant see you,I have 8 mirrors,count them, 8, and still cant see you if you are sitting behind me so close that you think it will save ya a buck, and that buck will not pay for your funeral. -- get real and learn how to drive. -- I drive 14,000 miles very month in a rig 20 times larger than your car,regardless of what yer drivin, and have no, zero, nada, accidents, because I know I have to always look out for idiots that cut off a rig,ride the trailer bar, or run alongside for some reason. -- Am a pro, you just drive to work. go figure who knows what their talking about.
      • 7 Years Ago
      Chris,

      The Interstates I drive (I-81 from Southwest Virginia and part of Western Maryland) are already like your virtual auto-train. Following distances of about 2 car-lengths are typical. I agree with the article that this kind of following distance is insane, but if you try for 150 feet, you'll end up with an SUV and a ricer cutting you off thereby reducing your spacing to the 2-3 carlengths. I typically see the cleanup of a couple of accidents on each 320-mile trip, and it seems that the cops are too busy cleaning up accidents to bother much with speeders, tailgaters, or left-laners.

      Anyway, this article has tempted me to go out and purchase a ScanGuage II. I've been thinkning about it for a while, but getting some real-time numbers on what happens when I pop into the passing-lane from behind a vehicle that I'm passing would be interesting.

      Anyway, no electronics required -- impatient people on an over-capacity highway will draft despite themselves, since they seem to think that tailgating the last car in a 10-car line will speed people up, regardless of the pileup risk. I'd love to know where you live so that I could move there, and share the road with sane, well-educated, safety-minded drivers! :-)
    • Load More Comments
    Share This Photo X