Despite its excellent fuel economy, on my youthful cross-country rambles in my VW Bug I sometimes found myself a bit tight on gas money. So I would draft trucks, as in really close up: ten or fifteen feet off their back bumper. I could just feel myself getting sucked into their vacuum shadow, and my throttle position eased up dramatically. According to Mythbusters, ten feet is the optimum drafting distance, resulting in a 40% to 50% improvement in fuel economy. Which explains how I eked out a 55 mpg average out of one tankful. But the view sure sucked. So I found myself thinking of ways to take drafting to the next level, where I could just turn the engine off altogether.
As in a hitch, that I could extend to hook my Beetle to the truck’s “Mansfield bar”. I fleshed out all kinds of permutations, although a giant magnet was not one of them. Wouldn’t it be wonderful, to hitch a ride, put it in neutral, and just take a nap? I guess my years of hitchhiking was making itself felt. As well as youthful daftness. Needless to say, like so many mental exercises, it didn’t ever get off the virtual drafting table. Do or did you ever draft trucks?
Ahhh, hypermiling. I recall a trip with a friend. He had a 74 Plymouth
Scamp with the slant 6. So far, so good. Then he rented a big double axle trailer to tow behind it. It was all that the poor little Scamp could handle. We drove to northwest Indiana to pick up furniture and things from his family and drove back. Whenever we started to get close to a truck, you could see the speedo start to move up, and you would pick up 5 mph without moving your gas pedal foot.
I remember riding my 500 Interceptor up the I-5 somewhere in Oregon, about 1985. As it was Oregon, it was freezing, even in summer. So, I would ride up next to a trucker point to the back of the truck and ask him if it was okay to draft. I never had one wave me off. So, I would slide in just behind the truck and get toasty warm from the engine heat coming up between my legs.
Problem was I couldn’t do it for more than ten minutes or so because the temperature gauge would slowly climb into the red. Still it was always a welcome respite! I’d scream by the trucker and wave; he’d always give a short blast on the air horn.
That is 25+ years ago. I wonder if this kind of thing still goes on in our age or total paranoia.
Hey Canucklehead, I still have my 500 Interceptor (or at least Mrs DougD has it). I keep thinking I should do a CC article on it.
I used to do the same drafting thing as Paul driving back and forth to Windsor U. I had a vacuum gauge on my car and as I tucked in behind the trailer bumper it would peg the gauge..
I wish I still had my Interceptor, no bike ever put a bigger smile on my face than that one!
Out of curiosity, how did you “ask him if it was okay to draft”? Is there some universal “drafting” hand signal I never learned as a kid?
This has easily become my favorite web site. As I listen to drivers who are maybe my age but certainly no longer teens, I realize that I wasn’t as far left on the IQ bell curve as I had previously thought.
Gentlemen, many of us don’t have 52 cards in our deck. Yes, I plead guilty to doing the above. With a bug though. I don’t think I possess sufficient testosterone to do it with a bike. My hat is off to you.
With all the donuts, bad weather, and now this – how did we manage to do our part in the perpetuation of the species?
I did this at the age of 21 when I was fearless and immortal.
I used to do alot of that, used to.
Without meaning to start a flame war, I’m gonna posit this: I don’t believe it.
Not for a minute.
Several reasons why: First, logical; engineering-wise, there’s no such thing as a free lunch. If, in the hypothetical, a car were being pulled by the air behind a truck…it would use as much horsepower and fuel as if there were a tow-rope tied between them.
And, then there’s the draft behind the CAR. Why doesn’t THAT pull it BACK?
Second: As an experienced cross-country biker, with a lot of (necessary but unwanted) Interstate time behind me; I know intimately what the air pockets feel like. Now I ride a near-naked bike, a BMW R1200GS – no fairings and a minimalist windshield. So I’m out there feeling it.
From a smooth airflow, as you get up around a thousand feet of a truck…you feel the buffeting. NOT a pull; a turbulence. And that turbulence only gets worse, the closer you creep to his backbar.
Now that turbulence is enough to keep leaves or litter suspended for a time, after having been sucked off the road by the negative air pressure of the truck body passing over (like a big, tall wing; same principle) but it’s not a positive suction you can glue onto.
Not you; not your car; not Bubba’s truck following, thinking he can save fuel. All he’s gonna do is get on the evening news and add a dozen gory photos to his Safety Manager’s portfolio.
You’re allowed not to believe it, but the science is very clear, and well proven. Ask NASCAR racers. And bicycle racers. Anyway, here’s some good discussion of the science involved: http://ask.metafilter.com/58487/Does-a-truck-work-extra-to-pull-a-drafting-car
Here’s more: http://mythbustersresults.com/episode80
Actually, you’re doing the truck a favor, because you’re smoothing out his abrupt pocket of vacuum; sort of like putting a rounded tail on his back.
Its well known racecraft not just nascar who cares on the logic it works and in one make racing is often the only way to pass
I used to ride my mountain bike (set up for roads, with smooth tires) a couple hundred miles a week. I was never particularly fast until one time I linked up with a bunch of road bikes along one of the SF bay area expressways. The shoulder/bike lane was wide enough to two bikes across and I got in the middle of the pack. My normal 13 mph ride (I used a speedometer to keep track of my rides) turned into 17 for my usual effort. When I left the pack, back to 13.
As I’ve read it, it’s a matter of fluid dynamics. A small body in a fluid has to deal with head and tail flows, with the back end pretty turbulent. If you can remove one of the problems (or share it with another vehicle) you can go faster. A few of the bicycle speed records were done immediately behind a draft-the first one I recall was behind a locomotive for about 60mph on the flat–with later ones behind cars with big fairings.
In NASCAR, I remember reading that drafting also helps the lead car somewhat.
For what it’s worth, it’s analogous to the fact that a long skinny boat is faster than the same displacement boat that’s short and dumpy. Think canoe versus dinghy. The side friction is a lot smaller than the head and tail wind effects.
Since you brought up bicycles you tickled a chord I had forgotten. I’ll see your 17 and raise you another 135 or so.
http://www.canosoarus.com/08LSRbicycle/LSR%20Bike01.htm
I had totally forgotten reading about this until you brought up the bikes. If you search you will find a bunch of these guys. I think going a152 mph plus on bicycle tires is more than I could handle.
Kind of remember that site. I was active in cycling 15 years ago. Couldn’t remember the numbers so didn’t quote it.
As it stands, 35MPH is as fast as my sense of survival permitted. I had a flat at 30 once and that was more interesting than I liked.
I have no reason to lie about drafting a semi. I did it and it warmed me up. Yes, it is very turbulent until you get right up close to the Mansfield bar but after that, it is smooth as a baby’s butt.
Would I do it again? Not at my age I wouldn’t.
I too have felt the difference while drafting, although I have never done it on a bike. I may have missed something in the earlier replies, but your experience could be different from Canucknucklehead’s because perhaps you weren’t as close to the Mansfield bar.
Ask Tom Cruise….he “invented” drafting in Days of Thunder……
One second behind a truck at 65 mph was the sweet spot according to the instant mileage readout on my ’87 Deville. Mileage went up 5 mpg.
Get right up close so you can get inside the buffet zone idealy 1 meter from the back of the truck and let the truckie see you if he dont want you there youll know but yep you can get fantastic fuel economy slipstreaming. Ive had people do it to me when Ive been in the Truck usually cars get scared of what the truck might do believe me trucks do nothing suddenly.
That’s the reason you can draft a heavy rig on an Interstate Highway; they do nothing suddenly, the just move along at 65 mpg as long as they can.
FWIW I’d strongly recommend against doing this with a CR England rig or anyone else who puts a large “1-800 Now Hiring” ad on the back of all their equipment. The business model of large van and reefer carriers is a requires a constant supply of green drivers feeding the beast.
In a much milder form I do this all the time driving into the prevailing headwind on WB I80 from Reno to Truckee. I try and stay 50-60ft (~1 trailer length) back where I still have situational awareness and the Driver sees me. IMHO getting any closer is penny wise stupid;1st time you strike road debris or worse you’ve negated all of your fuel savings.
No too long ago in one of the commercial vehicle trade rags a columnist proposed doing this on a larger scale where you have the intelligent cruise control sync to the truck and allow the truck driver in the lead to control a drafting road train of 4-6 cars. As “self park” is now an option on higher end cars its feasible from a technological perspective.
To make it work you’d need legal framework to pay the carrier and define liability in the event of a crash.
Ah, ya beat me to it. Such a proposition makes a lot of sense for professional driving…at least from an outside perspective.
Damn, I remember that site… I remembered the record as being north of 100mph, but the locomotive was my best recollection.
Cycling faster than about 35mph in short sleeves and shorts always offended my sense of survival. A flat at 30 was more interesting than I liked–the blowout of my LR tire on a clapped out MGB was mild in comparison. (Interstate and straight section.)
I’ll risk sounding ignorant and ask: why don’t I see more long-haul truckers drafting each other? Safety? Legality? Competitiveness? With readily available technology and a little software knowhow, one could turn I-5’s slow lane into a fairly streamlined “train” of semi-trucks. It’d save fuel and probably even be safer. Perhaps it’s just the engineer in me, but it seems so obvious.
That was common in Aussie for a time but got outlawed for a number of reasons
I don’t draft closely trucks but from my motorcycle days I think there is even some effect from near normal following distances. I’ll get behind them when towing my trailer, not tailgating, but enough to break the wind to a degree.
If you think that drafting on a motorcycle is a hair-raising experience, try it on a Vespa! I had a ’03 GT200 – would do 75 on the flat in calm conditions, but if there was any hill or headwind, it would slow to 60-65 *real* quick. I did a few freeway stretches on that bike, and I’ll tell you right now, the drafting effect is not only real, but VERY noticeable. I could easily maintain 70 with plenty of throttle left on all but the steepest hills. Sometimes, I could even gain enough speed to swing around and pass – NASCAR style.
You see one Nascar Sprint Cup race at Daytona or Talladega, and you’ll realize that drafting works.
I used to do this in my college days in a VW Diesel Rabbit. I was always short on funds, and even though Diesel fuel was half the price of gas back then, I often had to scrounge for change to pay for it. I found I could easily increase my MPG by ~35% or so by drafting trucks. I would always let the driver know I was back there, and few seemed to mind. Worked great at 55 MPH.
One summer (1969 to be precise) I worked for an artist in Chicago. I built a piece of sculpture for him which he was exhibiting at the state art museum in Springfield, IL. So we had to deliver the sculpture to the museum prior to the opening in his 1965 VW Microbus which he had painted with an op-art paint job (this was part of his fame as an artist). Most who have driven I-55 from Chicago to Springfield will tell you that this part of Illinois is flat. But to someone driving a VW Bus, it feels the road to Pike’s Peak. On the gentle rises one encounters on this stretch of I-55 the Bus would slow to 35 mph. This get’s rather tedious, especially when it’s 95 degrees outside, you’ve got lousy ventilation and no A/C.
Being a NASCAR fan I had read about drafting, and being young and dumb, decided to try it. First thing I learned is that it’s not easy hooking up with a semi in something as slow as a VW Bus. But I eventually did, and sumbitch, it worked! I was doing 65 mph! But following a semi close enough to get a tow takes a whole bunch of concentration. It’s tiring, but not nearly as tiring or aggravating as going 35 mph for miles on end.
With my bugs I always looked for a highway bus (coach). They travelled faster than the trucks (70-75 mph) and with the body much lower at the back had a much stronger suction. I logged up to 60 miles per Imperial gallon that way. There was a “sweet spot” about 1.5-2 seconds back that gave the best pull, other than right up on the bumper. With such a light, low powered car you could easily tell where to be.
i’ve drafted a time or two and enjoyed the slight buffeting that comes with the ride. most often in my 83 plymouth horizon that as a hatchback had a fairly flat rear. but i never drafted for long though because i always got paranoid about the distance and the fact that i could not anticipate having to stop. cannot see tail lights of cars 4-5 ahead. done with that idea.
As I grew up looking at the horribly mangled bodies of dolts who drafted thinking ‘ Truckers never do anything suddenly ‘ , I was deathly afraid of this practice , in the early 1970’s there was a (bullshit & completely dishonest) ‘ gas shortage ‘ at the same time that ordinary Citizens became enamored of CB Radios , long the darling of OTR Truckers so my idiot friends would ask a Trucker if they could draft him in their Honda 600 Coupe or whatever , it always worked out O.K. for them but many times a Big Rig has to lock ’em up because of others actions and anyone drafting at that moment ,even in a new Volvo , has a _very_ bad day .
I own several Russian Ural Motocycles , they’re 650 C.C. and make about 12 HP (kidding) so going uphill on the Interstate is a laborious process ~ -one- time I fell in behind a CalTrans Service truck , right where the driver could see me in his mirror , as mentioned , they’ll let you know straightway if they don’t want you there , I zizzed over The Grapevine @ 70 MPH instead of the usual 50 , couldn’t wait to get off and hit the two lane blacktops to Porterville .
In the winter , I’d tuck in a Convoy of Big Rigs when the temps dropped to 40° F or so , they bleed heat like mad so you needn’t be too close to be comfy and warm (if breathing Diesel smoke) at 80° F or so regardless of the ambient temperature .
Tailgating or drafting , scares me shitless .
” Ride scared , it’s a good way to stay alive ! ” .
-Nate