drafting semi's

[99metro]

If you are a REALLY slow driver like me, and look at 99 out of 100 cars in the fast lane that are "bunched up", you will notice that they are completely comfortable driving less than 1/4 of a second behind each other. Sometimes they are traveling 65+ mph and are less than one vehicle length away from the next driver. There might be a line of 20 drivers with this distance between them. This is why there are 70 car pile-ups.

Even my 2 to 3 lengths behind a 55 mph semi could be considered too close. At 55 mph we are looking at about 80 feet per second. Two seconds is about 160 feet. I am probably at the edge of safety on the very best of days. Something to ponder anyway.

[mattbatson]

Originally Posted by 99metro

If you are a REALLY slow driver like me, and look at 99 out of 100 cars in the fast lane that are "bunched up", you will notice that they are completely comfortable driving less than 1/4 of a second behind each other. Sometimes they are traveling 65+ mph and are less than one vehicle length away from the next driver. There might be a line of 20 drivers with this distance between them. This is why there are 70 car pile-ups.

Even my 2 to 3 lengths behind a 55 mph semi could be considered too close. At 55 mph we are looking at about 80 feet per second. Two seconds is about 160 feet. I am probably at the edge of safety on the very best of days. Something to ponder anyway.

well, believe it or not, I'm an ex cop and have handled a LOT of traffic accident investigations.
the VAST majority of them were failure to yeild right of way.
This means things like pulling out from an intersection into the path of an oncoming car, running a red light, changing lanes without looking, etc.
VAST majority.
Believe it or not, very few were from things like excessive speed or following too closely.

What you find with drivers following closely is that they have a heightened awareness...because they know the dangers...and as a result are not usually caught off guard.

Most accidents are from inattention, lazyness, etc... Not from people with heightened attention.

Also, unless some of you hypermilers have reduced the size of your brake rotors in an effort to save weight you should have no problem outbraking a loaded semi truck.

Unless you arent paying attention

Today I followed a semi from about 60 ft back at 61mph. i could feel the pull assist...although wont have hard figures until I get my scangauge...and felt VERY safe at that distance.

Also I have been accident free since my 20th b day, and I'm 41 now...so I think I have a pretty good handle on what safe driving is and what isnt.

obviously we all have a comfort zone when it comes to driving, and mine is probably a little skewed since I road raced for so many years, and am used to "close" driving at elevated speeds

[hamsterpower]

When I was 18, I coasted on a bicycle, behind a fire truck at 35 mph for 3/4 mile. NO effort on level ground. This was 2 feet off his bumper. When I turned away it was like opening the parachute. Kind of like the movie "Breaking Away". I know, stupid things kids do!

[mattbatson]

Originally Posted by hamsterpower

When I was 18, I coasted on a bicycle, behind a fire truck at 35 mph for 3/4 mile. NO effort on level ground. This was 2 feet off his bumper. When I turned away it was like opening the parachute. Kind of like the movie "Breaking Away". I know, stupid things kids do!

and you are correct.
when I was younger I would get right up behind semi's....which is getting dangerous

I recently discovered that you didnt have to be all that close at all to get a mpg benefit...which is why I started this thread.

[capnbass91]

I recently started drafting semis and trucks and love watching my mpg shoot up! Going 40 mph I was getting 45 mpg (I usually get 38-40 at that speed) behind a truck. And going about 58 mph I was getting 40 mpg (usually 28-32).
I don't know how close I am to the truck, but I don't get any closer to where I can't see the trucks side mirrors, so the driver can see me as well.

[mattbatson]

Originally Posted by capnbass91

I recently started drafting semis and trucks and love watching my mpg shoot up! Going 40 mph I was getting 45 mpg (I usually get 38-40 at that speed) behind a truck. And going about 58 mph I was getting 40 mpg (usually 28-32).
I don't know how close I am to the truck, but I don't get any closer to where I can't see the trucks side mirrors, so the driver can see me as well.

hey its a free boost in mpg!
Cant beat that!
no aero fabrication time/money necessary

I just ramble down the highway until I either approach a semi or get passed by one, then just file in behind at a safe distance...maybe 60 ft or so...and enjoy the fuel savings

[slowmover]

You need to be able to see the mirrors on both sides of the big truck. Any closer is too close.


okay, first off I know it is dangerous...

Ya, truck drivers are cretins, kinda like anyone who joins the military. Just thank them for their service. Out of sight, and out of mind.


.

[d0sitmatr]

ive always drafted larger vehicles, mostly semi's, and not at recommended distances either, as matt stated, if you cant stop faster than a fully loaded, or even an empty, tractor trailer, then there is something wrong with you or your car.
as a long time motorcycle enthusiast, its also why you >NEVER< tailgate a bike, because they have about 1/2 the stop distance of you in most situations.

I see, on avg, a solid 20-30% benefit from drafting semi's. but the vehicle also plays a role, as in I saw a much larger increase with my old ranger than I do in the mazda protege5 I now own. although I do see a pretty decent increase with the protege

and its quite easy to gauge the "pocket", if your being severely buffeted then your not in it
for cross windy days, try being in the adjacent lane on the opposite side of the truck from the direction of the wind (IE if your heading N, the wind is blowing from the E, stay in the lane to the trucks left side, put your nose about at the end of his bumper)
but make sure to allow for faster traffic, if you need to slow down and change lanes to allow people to pass, do so.

[wdb]

Originally Posted by d0sitmatr

as a long time motorcycle enthusiast, its also why you >NEVER< tailgate a bike, because they have about 1/2 the stop distance of you in most situations.

Uhhh, motorcycles in general need the same stopping distance as a car.

Motorcycle Braking - Motorcycle Safety Information and Resources

I don't tailgate them anyway, because I don't want to run over the rider when they fall down.

[sheepdog 44]

I live next to a UPS center. I leave for work the same time they do and when i can i draft them at a safe distance at 45 - 55 all on single lane roads all the way to work.

I would think a UPS, or delivery truck like Frito with a much larger rear are much better drafting choices. The pillow is much lower to the ground with less turbulence than a semi's taller rear where the pillow goes over the car. Behind a semi your really mostly driving into the less ideal turbulence in the undercarraige and wheels. It's probably safer too.