On UK roads, I frequently see cars driving very closely behind larger vehicles, attempting to stay in their slipstream, reduce drag and thus increase fuel efficiency.

Given the dangers of driving so close, are there any studies which demonstrate that the fuel efficiency savings are real and significant? If so, do they also study the road safety aspects of slipstreaming?

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    Mythbusters did try this out -- I think it was confirmed.
    – Sklivvz
    Sep 27, 2011 at 10:27
  • 3
    @sklivvz yep they did mythbustersresults.com/episode80 Sep 27, 2011 at 10:48
  • if you make it an answer, try to include some info until which distance there is a notable effect.
    – johanvdw
    Sep 27, 2011 at 11:43
  • 1
    It's not just lorries (trucks). NASCAR drivers know that every additional car added to the tail end of the train helps improve the mileage of every other car in that train.
    – oosterwal
    Sep 27, 2011 at 12:10
  • It's not just cars, marathon runners do it too. May 19, 2012 at 14:39

1 Answer 1


mythbusters found out it can increase fuel efficiency with 40% at 10 feet behind the truck http://mythbustersresults.com/episode80

Drafting behind a big rig will improve your car’s fuel efficiency.


To test this myth, the build team procured a car, a big rig, and a device that could measure a car’s fuel efficiency. They then drove the car behind a moving big rig at various distances ranging from 100 to 2 feet and measured the amount of fuel the car consumed. The Build Team discovered that the closer the car was to the big rig, the less drag is produced, thus the more fuel saved. At just ten feet, the car managed to increase its fuel efficiency by 40%. Drafting at two feet was slightly lower than the ten foot distance, mainly because Grant had to keep working the car pedal to maintain distance from the truck. However, that did not dispute the fact that drafting actually can increase your car’s fuel efficiency. However, the Build Team has warned that drafting is incredibly dangerous because the truck driver may not able to see you and you may not be able to react in time if the truck were to make a sudden stop.

the only video I was able to find was a 240p here you can see the full table http://www.youtube.com/watch?v=lttgT1XZVvE&feature=player_detailpage#t=534s

you can see that the economy starts at 100 feet with 11% saving over the control than as you get closer the economy increases up to 40% at 10 feet

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    Note that Mythbusters are not considered authoritative here: meta.skeptics.stackexchange.com/questions/450/…
    – Sklivvz
    Sep 27, 2011 at 12:55
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    @Sklivvz - Agreed, but it is a more valid data point than anecdotal evidence or pure speculation. It would be nice if anyone knew of any more rigorous studies, certainly the references of the wikipedia drafting page are no better or more relevant than the mythbusters reference.
    – Mark Booth
    Sep 27, 2011 at 13:07
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    @Sklivvz I recall that in this episode, they had aerodynamicists perform scale-model tests in a wind turbine, the Mythbusters' experimental results confirmed these findings. Still not a study, and further references would be good, but this appeared to be one of their more procedurally thorough experiments.
    – John Lyon
    Sep 27, 2011 at 23:04
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    @Rory A bicycle can equally draft behind a truck quite well. youtube.com/watch?v=Ss3fjLaCrRM
    – John Lyon
    Sep 27, 2011 at 23:06
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    yes, this was a well planned and executed experiment by them. I doubt any scientific institution is going to test this, as there's no scientific interest in doing so. Road safety aspects mean that no agency like the AA is going to test it either (as the distance you'd need to maintain is definitely, as stated multiple times by the Mythbusters) NOT safe). So this is probably the most rigorous study out there, even if not executed under totally controlled conditions.
    – jwenting
    Sep 28, 2011 at 7:08

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