MythBusters - Drafting a Semi
 

https://www.youtube.com/watch?v=lttgT1XZVvE

Check it out. Time to move on into the 10ft area!!

Only kidding of course. Saw this on YouTube and decided to spread the word! :thumbup:

that test is tested at 55 mph, and i rarely see semi's going that slow. besides, going 55 mph in most cars get very good mileage, anything after 55 is getting more and more worse


if they tested it at 70 mph, it would of been a bigger difference

I've been behind a semi, actually on the way to work today, he was going about 57.

As the video said - How many semi's go 70? If anything they should have done the test around 60-65 area.

drafting semis... good way to say bye bye to your windshield.

i was maybe 5 carlengths behind a semi today and still managed to destroy my windshield this afternoon.

You were probably too close for a good draft. Read the drafting link in my sig...in that thread, it is mentioned that 3 times the length of the truck is appropriate, and that 3 seconds is the most effective distance.

I have gained a lot of knowledge from the links in your sig. Thanks a whole bunch!!

It's hard to tell in a car. But on a bike you need to be very close to feel the difference. All I can say is that if the semi slammed the brakes you would face plant the trailer. I draft semi's when I need a rest when on my bike. I tend to stay at the edge so I could swing around if needed.

The semi trucks on the stretch of I-81 in West Virginia go 70mph or over usually, the speed limit is 70mph. I go 55-65 anyway. Haha.
It's difficult to keep up and draft them.

In my experience, no. A comfortable, safe distance draft really helps me go a lot further without getting so tired. Also, more appropriate when talking about drafting a car behind a big rig, drafting a group of bicycles or a slow moving car really works great.

You don't have to overlap wheels, or even ride so close that you can't look ahead for fear of having to stop suddenly. You don't feel the wind sucking you, you don't go much faster, but you save energy for sure. It even works for slow riders.

I watched this on Mythbusters. The guy driving said it was scary and very uncomfortable driving so close. Drafting semis less than 2 seconds away is an amateur's way to hypermile, IMO. There's nothing scarier than following an 8 foot wide by 12 foot high wall at any speed, not knowing when that wall is going to come to a sudden halt - and I really hope whoever is doing that is paying attention. It's sort of like those people that like to drive the speed limit in dense fog; you just don't know if a stopped car is going to come into view...

I don't ever want to exit my car by way of the windshield, and if I DID make it through in one piece, I certainly don't want to faceplant the very thing that forced me through the windshield in the first place.

Nice to see somebody found the video I posted. I don't know why I never thought of posting it up on here. Sorry about the quality, I saw this on once before church so I threw a DVD into the recorder right before I left, and the transfer from DVD to computer didn't go so smoothly.

Mythbusters seem to get pretty good results. I assume they used cruise control, they never actually say if they did or not. I've never had the oppurtunitie to draft semi's regularly. When I start college soon I'll draft them as much as I can and see which results I get.

No, they didn't use cruise because they were trying to maintain a specific following distance.

-Jay

Oh alright, I suppose that makes sense. If you were able to find a semi that was cruising at a constant speed and you were able to use cruise control while drafting him, it should be possible to obtain results better than Mythbusters. Thats what I'm hoping to try out, but I have to install cruise control in the Civic first.

In my experience that's nearly impossible as big diesels and passenger vehicles have different torque curves so their cruise controls behave differently. I remember once on our old Bonneville dad picked up a junkyard cruise to replace the broken one. The junkyard cruise came out of a diesel and it was really accelerator happy. It took forever to get it adjusted so it would hold speed properly, but it was still jerky, not nice and smooth like a cruise should be. We ended up taking it back and exchanging it for a non-diesel cruise.

-Jay

Some of the newer expensive cars have smart cruize with sensing in front which slows the car down when it is going to hit something and even applies the brakes if needed - gets a little tricky on turns with guard rails!

smarter than drivers :D

Uhh, a bit off topic I know but... Really? I'm the least techie member of a very techie family and I end up yelling at the TV every time I watch Mythbusters... My brother has the same problem with the mistakes they make. Please don't think that their results are even the least bit scientific or applicable to the world at large. They are usually not good analogs for the question at hand, not repeated to any number that is statistically valid, and only test a very narrowly defined set of conditions. Then they take the results and make blanket statements about broadly defined problems.... The show is entertaining, but please don't think of it as anything but that. (That being said, I LOVED watching them blow the cement truck all to hell! :) )

ya i like the "show" but many things they do isn't thought out

my scangauge confirms in my neon that fuel consumption at 75-80 drafting is the same or less than 65 all on my own. catch up and 'hang on.' if i drive 55 im sure it would be much different data, but i take advantage of what i can where i can.

This whole thread proves how important aerodynamics is
 

This whole thread proves that aerodynamics is very important. I have drafted Semis before to test and it does make a huge difference. My mileage on my DIC went up from 30 to 48 and stayed there for until I pulled out from behind him and then it went immediatly back to 30.

Once about 10 years ago on a winter day here in Texas it was about 80* when I took off for a ride to watch a friend race about 80 miles from home. The race ran way late and a bad cold front came in dropping the temps in the 40*s or even high 30*s. My leather jacket and gloves were not enough and I froze my tail off trying to get home. I got in and drafted a semi for about 20 miles to get out of the wind, I know it was stupid but it was much warmer out of the wind. Generally I am prepared for such emergencies but that was more extreme than I was prepared for. It was a very strange feeling because when you get up close the wind just stops even though you are still going 70 MPH. That also makes me think of how important aerodynamics is. Curly

Reminds me of drafting a garbage truck this last week on my motored bike. I think the driver was expecting to just pass by me, not have me tucked firmly in his wake at 35 mph.

I don't make a habit of that and it was really the first time I did it on the motored bike. It scares the crap out of me for obvious reasons.

Wow...you are really committed to it, if you're willing to draft a garbage truck. :D

I had a rock from a dump truck hit my windshield. No damage, but I wasn't drafting. :eek: Trucks are a fact of highway driving. It can happen without even drafting as well. Drafting of course increases this risk.

Well one of the reasons I no longer ride a regular motorcycle is because of trucks and crap flying off of them. I only got nailed once directly, but it was about a 1 foot long splinter of scrap lumber that hit me directly in the chest. I saw it lift right off the flat bed it was on and come right at me. There was absolutely no way to avoid it. Fortunately it was neither sharp enough nor heavy enough to even cause any pain, but it left me even less complacent about such things.

I also worked as an auto liability investigator and heard plenty of tails of objects from trucks damaging cars - including a 50 lb electric motor that rolled off of one, and down the lane to ultimately bash into the front end of another car going the same direction. Obviously, to a motorcyclist, that would be a very bad thing to face!

Drafting too close limits your options to deal with such hazards.

Oh, don't get me started on unsecured loads. I've witnessed too many accidents caused by blown-off loads, including one very spectacular fatal one. I do recommend that (unless you're on a motorcycle) you just head straight for whatever random road debris has surprised you, rather than swerving to avoid it. In my observation, the swerve causes far more damage on average, since far too often it results in a collision, spin-out, or rollover...and the debris is usually something pretty harmless, like a 2x4 that even a lowered Civic could roll over, or a bouncing empty rubbermaid garbage barrel.

I have had a large rock hit the windshield and shatter it, almost coming through on a test drive of a customers car. It came off a tire from a vehicle travelling in the opposite direction. I paid for the glass replacement out of my pocket.

I had to completely stop in a 45 MPH divided 4 lane road to avoid a falling pine tree that covered all 4 lanes, and missed a school bus by 5 feet. Had to move the pieces of tree to continue down the road.

I swerved once to dodge a tire and wheel that came off a car going in the opposite driection. It had been hit by another car already and launched 40 feet into the air.

I watched a 64 Rambler station wagon once loose its right front tire, wheel and brake drum. The driver kept going down the road and stopped at a light. The car was balanced so the suspension where the missing wheel was located never hit the ground, until the driver stepped on the brakes (early Ramblers had dual systems before it was legally required). The driver turned left and drove away.

I had a friend whose brother was run over on a Kawasaki 900, by a woman in a Dodge Dart. The police followed the trail of body parts and motorcycle parts to the womans driveway. She told them she never knew she hit anything.

I had another friend whose Chevy van hit a deer, the deer came through the windshield. They had to open the side door and let the still living deer out of the van.

I know a cop who saw a guy fall off a motorcylce for no apparent reason. When he stopped and asked the guy what had happened, the bike driver told him a big bug had hit him square in the chest. When he showed the cop the mark where the bug had hit him the cop issued no ticket to the driver.

I try to avoild driving at night!

regards
gary

I live in Ohio, they are really tough on big trucks here. Just ask any trucker. Most trucks NEVER exceed 60 mph around here. So I often draft a 55mph truck. Other states I've driven in are not that way. Indianan for example, trucks do ~70 on he turnpike all day long...

I draft every time I'm on the interstate. I've seen as high as 46.7mpg on a trip from Cleveland to Cincinnati drafting about 200 miles of the 250 mile trip and using a HAI.

My gas log tells the story...

HAI remains my only true mod, and it's crude and not as effective as it could be. The suggested temp is around 180*F at full speed, which I've never attained. (only in stop and go traffic actually)

I draft at about 1 truck length back, just a hair off center and use my headlights so they can always see the gleem of me behind them. If you draft in this manner, at least what I've seen, the semi drivers won't mind a single bit that you're back there. My tank average on the way back from Cleveland this time was 39.8mpg when I arrived in Cincinnati. Currently adding city mileage to this tank, but I'm going to fillup short of a full tank so I can record the good mileage! :)

If you're determined enough, you can listen closeley as you move within correct drafting range and hear that wind noise is substantially less, turbulance is much less, and at 1 truck length back, you're safe from getting pulled over from tailgating and Semi drivers are now doing about 60mph in my area, so they keep you at a perfect speed.

I have had 2 broken windshields from trucks and one was from a truck coming in the opposite direction going around a curve on a 2 lane road. And one time something came off a truck in the other lane on a 3 lane highway at highway speed and bounced on the road in front of me. It was pieces of tire. Also had a semi jacknife up ahead of me in an ice storm once. Luckily there was nobody there. Good thing he didn't hit anybody. I stay far far far away from trucks on the road.

Just my experience.

Well said Dave.

I actually follow the suggested 2-second rule when drafting. It's fun being able to tell people we get over 38 mpg in our minivan.