drafting semi's

[tinduck]

My 2 pence (caution, only for european road conditions):

1) Road debris is not an issue over here. On the autobahn, nothing survives more than 30 seconds before being shredded and cast aside :-) If there is something substantial lying on the road, police will be quite quick to clear it. And if you want to anticipate every possibility, you need your whole stopping distance as a safety cushion anyway. This will only work at 3 a.m. though...

2) In my optinion, the old 3 second rule is for half-asleep drivers in mediocre 60s cars (you may call that worst case). A modern car can stop inside 40 m (app. 120 ft.) or better on dry road from 100 km/h. Given the fact that a trailer rig will stop AT BEST as fast as a normal car (in any weather condition), we only speak about reaction time which must be buffered by the distance between truck and car. For an alert driver, one second should be quite luxurious, which translates to 22 metres at 80 km/h.

3) Give the truck drivers some pause... neither are they idiots, nor do they drive as clueless as many car drivers do. The overwhelming majority of truck drivers I have encountered do not mind someone using their wind gap (though not many of them know they even save fuel when someone tailgates them as he fills up their energy-consuming low pressure drag pocket) and drive very anticipatory to conserve their fuel.

The only time I had to hit the brakes hard when trailing a truck was when that guy slammed the brakes because I was trailing him. It was a good adrenalin rush, but far from a close call. And that was one case in a whole year of rather intensive drafting.

Most hairy situations I encounter arise from people not looking where they want to drive but just driving there...

To provide some numbers:

usual trip to work yields around 4,0-5,1 l/100km depending on how much I can use trucks for drafting (scangauge numbers). The extreme numbers are more due to head- or tailwind and other weather and traffic conditions, I would say between 4,3 and 4,8 l/100km is the usual range. So 10% is a good estimate of the savings. Maybe less for a car with low cd value, my van has one near that of castle Neuschwanstein.

so long,

tinduck

[JasonG]

With the FE savings I've never understood why truck drivers don't like tailgaters ?
Worried about a windshield ?
If rear ended, the rear driver is (normally) at fault.
For the drivers here, does it make the trailer dance ?

[slowmover]

A big truck has significant blind spots, all around it. I've had trucks with as many as 13-mirrors, most with 8-mirrors to try and keep up with all that is around me. As what is behind me is at least as important as what is ahead of me in uncountable situations, knowing where all the other vehicles are is critical.

Truck tailgaters are assholes, pure and simple. Guys whose concerns are to be ignored even though we all share the road, little different than the false thank you to a veteran . . . geez, glad it ain't me hump'n it. Truck driving is a high fatality livelihood. No cop will ever see the combination of shortened lifespan and on-the-job fatality rate as do truck drivers (or, farmers, fishermen, etc) and he has a defined benefits pension after 20-years plus union protection throughout his career. So where is the truck driver memorial? The drivers retired at age 52? Few and far between. Almost non-existent. One of these is productive, the other sucks up tax money. Which do you pay more attention to while next to them in traffic?

Some tailgater suddenly comes out of the shadow into an adjacent lane as you're starting to change into that lane because of what is ahead, etc, well, guess who'll be held to a higher standard if there is a wreck? Guess who may be fired, or forced back into a backbreaking low-paid truck job, or lose all the years of a career as a result of an asshole. We're all humans and make mistakes, but taking advantage of another man in order to save some pennies is past unconscionable.

Stay back far enough that the tractor mirrors on both sides are always visible.

One can get the distance correct and the other traffic will flow around if the man following the big truck uses headlights/tail-lamps constantly. A little brake-light action can get the next pack of cretins the idea that staying left is beneficial. Not doing any lane-changing with the big truck breaking trail is worth more than getting in closer.

When you find that geosynchronous orbit back there, and know how to define it for others to get them around both vehicles then you have a good relationship going. Keep the distance perfectly constant if you want the Merit Badge.

Also:

Always pass a big truck with at least 5-mph speed differential. Get off the cruise and get on it. You want a noticeable amount of "positive throttle" to overcome the big truck bow wave. Change back into that lane about a football field ahead (no joke, you've no idea who's driving that truck, what shape it's in, or how heavy it is). This is not quite hyperbole. Smoothness will come with experience, and FE won't suffer noticeably.

Never, ever ever get stuck next to a big truck while behind another vehicle. Wait till the other vehicle is fully past the big truck (with room to move back over) before making your dash. Wait your turn, but jump on it to keep the one behind you from staying close to you as you pass. In the wait, cut off the other a-holes from moving from behind the truck to between you and the truck you as you wait for the first guy to get past. Defend that territory until you launch.

Stay out of packs, and you won't have the problem. Slow down a half-mile back to have them get around the big truck and you'll not have to do any more than maintain the necessary minimum speed differential while passing. You can learn to take advantage of terrain and actually be slowing as you pass the big truck to hit your intended mark ahead of him to get back to the right lane. If you can do it towing fairly heavy, the beer is on me.

Remember that if something goes wrong with that big truck when you're next to it then the Jaws of Life are a handy tool to help get the trailer unstuck so it can be turned upright and shoved out of the way. Their intended use is irrelevant over 4,000-times per year






.

[99metro]

Never, ever ever get stuck next to a big truck while behind another vehicle. Wait till the other vehicle is fully past the big truck (with room to move back over) before making your dash. Wait your turn, but jump on it to keep the one behind you from staying close to you as you pass. In the wait, cut off the other a-holes from moving from behind the truck to between you and the truck you as you wait for the first guy to get past. Defend that territory until you launch.

Amen to that! EXACTLY what I do all the time. I see 3 cars right next to a big rig and I think this could get real ugly. I back off these scenes to prepare to take defensive action if something does happen. Folks take huge unnecessary risks all the time and one day they will lose that 9th life.

[JasonG]

Side note on not hanging out next to a big rig, ever see a tire come apart?

Thanks Slowmover !

[usergone]

Going about 60 mph, I see something like 3 lbs of boost. At 70, it can get up to 7 or more. If I get behind a semi at about 30 metres, I can see a reduction in boost. But because of the increased effort to try to stay at that distance, I sometimes find myself playing catchup and having to accelerate more than just cruising.

As far as truck drivers liking or disliking a drafter, I find that it is hit or miss. Sometimes they'll do nothing, and sometimes they seem to change lanes more than a semi normally would. When they start doing that I let them go cause I don't want to make them angry.

Now I just need to mount a strip of rare earth magnets on my bumper...

[slowmover]

Originally Posted by JasonG

Side note on not hanging out next to a big rig, ever see a tire come apart?

Thanks Slowmover !

Welcome.

Next time any of you pass a tractor-trailer, be aware that each tire on your side of his vehicle is carrying near to 4,500-lbs. Times 9. The oldest tires are on the trailer, and they get younger as you go forward, axle pair by axle pair; second re-tread, to first re-tread, to new in standard practice. As you come up on a tractor-trailer look at the tires: see any wobbles, bulges or (yes) missing tires? Haul butt, boys, if you're feeling brave.

And to the above: Don't assume you can read the truck drivers mind based on truck movement. In most cases you're messing with someone with more driving skill than you've imagined is possible. You don't know that you don't know. Were your income dependent on it, your skill would also increase (conversely, trucks from Swift, Werner, Stevens, Schneider, Crete and some others are populated by low skill rookies; double-beware), so if that driver wants to F with you he can, before you're aware of it in many instances.

A slight rise in the road, a downshift, engage engine brake lightly and your ecomoddin' headlights will be kissing mudflaps before you realize it. Essentially, once the car "disappears" from view, the evil truck driver can stomp the service brake and you won't have time to pucker. Not all big trucks are loaded heavy, and can stop much faster than you expect.

IOW, don't assume that because your rolling beercan will hypothetically stop sooner than a big truck that it infers invulnerability. The above example is only one way that big trucks could screw with you, highly unlikely though that is.

Unsaid are the mechanical problems that could cause a truck to rapidly decelerate.

Plus, it ain't because of ETD's that the ICC Bumper below the deck is now required:




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[reb01501]

What are ETDs? I doubt it's Express Tire Delivery ...
End of Train Device?

[wdb]

Yes truck drivers have a tough job. That doesn't make them all good drivers. I've seen more than a few complete yahoos behind the wheels of semis.

What I'd really like to see is semis in the US designed more like the European semis. When I drove in Italy, the trucks were well equipped with aero aids, and generally designed to a have lower center of gravity than the trucks here. They also appeared to have pretty strictly controlled speed limits, significantly lower than the limit for smaller vehicles; every semi I saw in two weeks of driving in Italy was in the right lane, and moving more slowly than my little 1 liter Fiat - which was far from the fastest vehicle on the road!

http://www.youtube.com/watch?v=W-fMWpCokn0

[sheepdog 44]

Today as i pulled into the parking lot at work i saw a truck with one door open flailing into the lane over and closed again! He mustve just pulled out of the Pricechopper loading dock and forgot to lock it. I wouldnt want to be behind that when soup cans start falling into the road. Or maybe i would, as in a recent news story around here about $200,000 falling from a moving money car.

Okay, how much of a benefit do you get from drafting car, as opposed to being being drafted by a tail-gater? The most gas saving mod appears to be a boat tail, so would you benefit more by having that low pressure behind your car being filled by a tailgater? Or is it best to draft behind a car? Theoretically speaking of course.