Mythbusters Drafting episode

[Ryansmagic]

Truck drivers HATE THIS! They can't see you, so when they are going to change lanes and they look back, nothing is there, then 5 seconds later you switch lanes to pass, you just apear there to them! bad situation....

[fosley]

Ok, as long as you have enough distance for reaction time, you shouldn't have any trouble out-braking a semi. Seriously, what has a longer stopping distance besides a train? Next, since you're behind the semi, it doesn't matter if he changes lanes because you aren't there for him to hit. Or, to say it differently, if a semi driver *tried* to hit you, you'd have to be paying no attention for it to work.

Note that this works for things besides semi's also; my friend and I tag-teamed a trip back from Albequerque, NM to Tucson, AZ with a Fiero/MR2 combo and got 10-15% better gas mileage. You have to switch out every 30 minutes or so to even out the savings so both tanks deplete about equally, but this is a good thing since it makes the trip less tiresome since you alternate between pacing and navigating.

However, something to note: air resistance plays a big role in stopping from high speeds. If you are drafting and try to stop at 80 mph, it will be harder than stopping from 80 mph in open air because you are lacking the aid of air resistance. Not enough that a semi will out-brake you, but enough to catch you off-guard. Normally, I slow down by letting off the accelerator and very rarely need my brakes on the highway. Drafting the Fiero though, I also had to move to one side or the other to catch some wind, or he would engine brake much faster than me, requiring the use of my brakes.

[20incher]

This is the same technique nascar has been using for years, they stay in 2nd and let the winner use up alot more gas then they are going to have to. Then at the end pull ahead and take the race. On a sidenote i just have a problem with having a vehicle in front of me...just annoys me. *shrugs*

[breadbooze]

Trying to justify unsafe driving practices for the sake of saving gas is pretty lame, for lack of a better term. Surely a MR2 can stop quicker than a semi, but you will lose the big picture; what's happening on the road ahead of the semi. You also take away an out; the space cushion ahead of you is the ONLY out you have control over.

[Bak@EMSPowered]

Originally Posted by breadbooze

Trying to justify unsafe driving practices for the sake of saving gas is pretty lame, for lack of a better term. Surely a MR2 can stop quicker than a semi, but you will lose the big picture; what's happening on the road ahead of the semi. You also take away an out; the space cushion ahead of you is the ONLY out you have control over.

Logic won't work with these folks... just wait, there'll be more replies to your post about how its super safe and doesnt harm anyone...

[fosley]

Originally Posted by breadbooze

Surely a MR2 can stop quicker than a semi, but you will lose the big picture; what's happening on the road ahead of the semi.

Ok, but you have to stay *way* back to really see anything of use around a semi, so "normal" driving won't help that aspect much, if any.

[flamesuit][grammarnazi]In this case you're saying "To be sure, an MR2. . .", which is shortened to "Sure, an MR2. . .", rather than "surely". And since I'm here, it's "An em-are-two", not "A em-are-two".[/grammarnazi]

Originally Posted by breadbooze

the space cushion ahead of you is the ONLY out you have control over.

Not if you have a built-in ejection seat. Sheesh!

This is a problem if there's another semi right behind you, but it's not really a problem normally. Whatever's in the road up there will get creamed by the semi (and therefore give you plenty of room to stop), and if he dodges it, you only need 3-4 semi-lengths to come to a complete stop, or you can just follow him over, or probably just brake hard and drive onto the shoulder, or go around on the center line.

We'd need to do some research, but the question becomes: does the increase in accident probability from following "too closely" outweigh the decrease in accident probability from not exiting/entering the freeway as often? I really wouldn't think so, but like I said, we'd have to do some research to be sure.

Edit: The other fallacy I see very often is that it's more dangerous to tailgate a semi than a car, which I say is untrue. If you are X distance from both, you're more likely to rear-end the car if he tries to stop (he stops faster), you probably won't have as much warning between the time he swerves and you realize there's something in the way, and the time you hit or miss it (the semi gives you a guaranteed 50-60 feet + follow distance, while the car gives you 15-20 feet tops, plus the car is more likely to wait until the last second to swerve, plus the semi is more likely to see it coming to begin with and just slow down), and if the semi hits something, he's more likely to push through and give you a path, while the car is more likely to come to a very rapid stop in your face.

[breadbooze]

Originally Posted by fosley

Ok, but you have to stay *way* back to really see anything of use around a semi, so "normal" driving won't help that aspect much, if any.

Which is EXACTLY what you should be doing to begin with. 4-6 seconds under 30mph, 6-8 over 30. Very conservative, but years of driving UPS semi's have it drilled to my head.

[flamesuit][grammarnazi]In this case you're saying "To be sure, an MR2. . .", which is shortened to "Sure, an MR2. . .", rather than "surely". And since I'm here, it's "An em-are-two", not "A em-are-two".[/grammarnazi]

Cool. Though I was taught you use "an" when preceeding a vowel. That was in 2nd grade, it's been a while.

Not if you have a built-in ejection seat. Sheesh!

This is a problem if there's another semi right behind you, but it's not really a problem normally. Whatever's in the road up there will get creamed by the semi (and therefore give you plenty of room to stop), and if he dodges it, you only need 3-4 semi-lengths to come to a complete stop, or you can just follow him over, or probably just brake hard and drive onto the shoulder, or go around on the center line.

We'd need to do some research, but the question becomes: does the increase in accident probability from following "too closely" outweigh the decrease in accident probability from not exiting/entering the freeway as often? I really wouldn't think so, but like I said, we'd have to do some research to be sure.

Edit: The other fallacy I see very often is that it's more dangerous to tailgate a semi than a car, which I say is untrue. If you are X distance from both, you're more likely to rear-end the car if he tries to stop (he stops faster), you probably won't have as much warning between the time he swerves and you realize there's something in the way, and the time you hit or miss it (the semi gives you a guaranteed 50-60 feet + follow distance, while the car gives you 15-20 feet tops, plus the car is more likely to wait until the last second to swerve, plus the semi is more likely to see it coming to begin with and just slow down), and if the semi hits something, he's more likely to push through and give you a path, while the car is more likely to come to a very rapid stop in your face.

Accidents don't "normally" happen either. Better to avoid the abnormal than to assume things are always normal.

Trying to justify unsafe driving practices by quoting physics formulaes and drawing up ambiguous figures to support them is lame at best, for lack of a better term.

Have you plowed into a deer that a semi ran over?

[fosley]

Originally Posted by breadbooze

4-6 seconds under 30mph, 6-8 over 30.

Well, I think that's overkill (unless you are driving a big truck or something), but I won't argue that it isn't safer than being 3 car lengths back at 70 mph. I normally drive about 1 second back in-town and 2 seconds back on the highway. I also back off when I'm not in a sports car with good brakes (a rare occurrence). My problem with 6-8 seconds is that by the time I can determine how rapidly they're braking, I'm 3-4 seconds away, but have to do a lot more stopping because they got a few second headstart on me.

Originally Posted by breadbooze

Cool. Though I was taught you use "an" when preceeding a vowel.

The difference is that "MR2" is an acronym and pronounced "em-are-two", not "mur-two". "An" for a, e, f, h, i, l, m, n, o, r, s, u, x; "a" for b, c, d, g, j, k, p, q, t, v, w, y, z.

Originally Posted by breadbooze

Accidents don't "normally" happen either. Better to avoid the abnormal than to assume things are always normal.

What I meant is that you have to pay attention to what's behind you. If a car comes up behind you, back off a bit, and if a semi is following you, obviously you want an even bigger forward buffer. But most of the time, where I drive anyway, there's nothing behind me to worry about.

Originally Posted by breadbooze

Have you plowed into a deer that a semi ran over?

I've plowed through the debris field of a Porcshe that a semi ran over, but no deer. I don't really see deer being a problem though. First, the semi will probably hit his brakes to avoid the deer, so you'll already know something is up. Second, when he hits it, even if it goes straight under the semi, it will get accelerated to high-ish speeds, so when you see it coming at you under the semi, you won't be doing a 25 foot panic stop from 70 mph, but more of a 100-200 foot panic stop from 60 mph. Third, most of the deer I've seen get hit by a semi went to one side or the other. Fourth, it will be a lot more dead if a semi hits it first, and less likely to kick you to death through the windshield. Fifth, hopefully it'll be on the ground by that time and you'll strike its body with your bumper, rather than taking out its legs and having the body come through the windshield into your lap. Given the amount of crap a deer would have to go through to get to your car, I'd say you're probably safer from deer while following the semi than not. Especially if the likelyhood of a deer strike is high. Not necessarily less likely to hit it, but safer.

But in my experience, you're far safer tailgating a semi than you are passing it. I've been forced to drive off the road and/or stomp on the brakes to avoid getting hit by a swerving/sliding semi more times in the past 2 years alone than I've ever had problems with tailgating one. So while it may be more dangerous than following way back, it's not really that dangerous in the grand scheme of things.

[breadbooze]

It's all fun and games until the shit hits the fan.

I'll thank you for raising my insurance premiums at a future time.

[Bak@EMSPowered]

^^ Yup

[JMcDonald]

I do think it could be more dangerous (although, as Fosely pointed out, it seems you are a little bit safer than hitting a deer on your own, or swirving to miss it and hitting a tree) than following at a safer distance. However I am quite interested in trying out the tag-team thing next time Im on a road trip with friends. Although Id have to be in front the whole to for it to reotely even out, since they all drive 18 MPG Supras .

[MR2SW22]

i was about 4-5 car lenghts behind a semi for 150 miles on the way back to cali a week ago, it was producing 28-29 mpg on my 91t, it's got an intake 2.5dp so it's basically stock, then again my motor's 1st cylinder is low on compression so i bet if the engine was working better then i might have gotten over 30mpg. but as people were saying it's not the safest thing to do, when they would change lanes, i would drop back a couple more car lengths to let them see i was there but i wouldn't ever try 20-30 feet, thats just crazy.

[Bak@EMSPowered]

Originally Posted by MR2SW22

i was about 4-5 car lenghts behind a semi for 150 miles on the way back to cali a week ago, it was producing 28-29 mpg on my 91t, it's got an intake 2.5dp so it's basically stock, then again my motor's 1st cylinder is low on compression so i bet if the engine was working better then i might have gotten over 30mpg. but as people were saying it's not the safest thing to do, when they would change lanes, i would drop back a couple more car lengths to let them see i was there but i wouldn't ever try 20-30 feet, thats just crazy.

Isn't that pretty normal MPG for an MR2 on the highway?

[MR2SW22]

Originally Posted by baktasht

Isn't that pretty normal MPG for an MR2 on the highway?

i just found out 2 days ago i have had #1 cylinder is busted, 90psi compression on that cyl, and 151-152 on the other 3, and i consumed 2-3 quarts of oil in 250 miles of the 350 trip. and yes, 28 mpg is normal for a normal operating 3sgte.

[3sgtepower]

As nice a fuel economy percentages those are, I would never draft in a car I cared about. I was once riding with this eclipse gs ricer that had put on a $3000 turbokit to his 420gay. He was real proud of his 175whp beast and showing it off to me.

He got right behind a dumptruck, and I said I wouldnt hang behind it cuz it might hit your windsheild with a rock, and then he talked about how drafting large trucks saves so much money in gas. Then the dump truck let out a bunch of fist sized rocks, and a couple of them punched larged holes into his FMIC

I didn't wanna say "I told ya" cuz he was pissed, but lesson learned.

[JMcDonald]

Originally Posted by 3sgtepower

As nice a fuel economy percentages those are, I would never draft in a car I cared about. I was once riding with this eclipse gs ricer that had put on a $3000 turbokit to his 420gay. He was real proud of his 175whp beast and showing it off to me.

He got right behind a dumptruck, and I said I wouldnt hang behind it cuz it might hit your windsheild with a rock, and then he talked about how drafting large trucks saves so much money in gas. Then the dump truck let out a bunch of fist sized rocks, and a couple of them punched larged holes into his FMIC

I didn't wanna say "I told ya" cuz he was pissed, but lesson learned.

Heh, I probably wouldnt draft semis either. But I am still curious about doing it with another friend in a car.

BTW, I got 30 MPG in a stock MR2 going to NA2005. Did quite a bit of boosting, and had the AC on.

[MR2SW22]

Originally Posted by JMcDonald

Heh, I probably wouldnt draft semis either. But I am still curious about doing it with another friend in a car.

BTW, I got 30 MPG in a stock MR2 going to NA2005. Did quite a bit of boosting, and had the AC on.

makes me think that i could have bee around 30mpg if i had proper compression

[fosley]

Here's me drafting a semi:


Unfortunately I got no benefits, as we were driving at a lower speed than my speedo registers for 10+ miles. Stupid construction zones.

[Roger_Rabbit]

I drafted earlier today... I pulled between the draftee (truck in front that I am drafting off of) and the drafter (another truck that was about 35 foot behind the draftee)... It was fun till I had to exit...

[Bak@EMSPowered]

Originally Posted by Roger_Rabbit

I drafted earlier today... I pulled between the draftee (truck in front that I am drafting off of) and the drafter (another truck that was about 35 foot behind the draftee)... It was fun till I had to exit...

real smart.