Driven to Save -- Opinions Needed! (hypermiling book author seeking feedback)

[SentraSE-R]

I'm in for the Full Monty.

[Slasher]

Kewl vision!!! I am a newb on here... But have been a lurker and have trained myself to slow down and watch my mpgs rise.... I think that there are various methods or strategies if you will to employ at different situations to maximize mpgs... It's the what when that gets you...

I think the greatest thing is vision of what happens ahead of you and reacting accordingly... Like you do when you ride a motorcycle... The S.E.E. (or S.I.P.D.E.- for the oldtimers) acronym used in the M.S.F. courses... Except in hyper-miling, you try to keep as steady speed as possible and avoid decelerating and accelerating to maximize mpgs...

What works in my Yaris,is a lil different from my old VW cabrio or the old TDI Jetta I used to drive...

[Richard Rowe]

AWESOME!!! I knew you guys wouldn't let me down. Right now, I'm combing back through the chapters just to smooth things out and make it palatable. I usually don't show anything before the fourth draft, so this is a first for me. But, I've been wanting to write this book for so long that I dare not risk screwing anything up with inaccurate information. My editor is a good guy, and he knows loads about cars...but I'm supposed to be the (relative) expert here.

@ Frank Lee, Jakobnev, Metro MPG: No problem guys, you're on it. I'll send you the whole thing probably tomorrow or the next day, along with anyone else who wants in. As of right now, it's about 120 pages (plus I'm expecting another 10 before rewrites are done)...about 95 percent print, the rest pics and diagrams. But, once you adjust the margins and font and all for the style that eMap Petersen uses for everything, the current text would go about 160 pages. Adjusted for ebook, 275 or more. Just letting you know what you're in for

@ Eco generator and Brucepick: Yeah, I've been playing with the idea of pre-releasing the full thing here...personally, I like it. BUT, what my publisher thinks may be a bit different. I kind of doubt that DM or Emap would be terribly thrilled that I released their book in finished form online before it was published. Might cut into sales by, ohhh, 98.5 percent or so. So, that probably ain't gonna fly. But, that doesn't mean I can't release parts of it, or like a 10-page condensed version. I could justify that as a marketing tool. Really, I shouldn't release the whole thing for review to anyone by my Ed. When writers do stuff like this -- WHEN we do -- it's usually just a chapter to one person, a chapter to another person, and none of them know who the other ones are. But, that won't work here, because the book's written in narrative form...every chapter's built on the ones before it. So, screw it. I want this thing to be perfect.

@ Vman455: See, that's EXACTLY what I'm looking for. But (and understand I'm not arguing here), weren't the late 2006 models released as 2007 models? I pulled the Viper Stats from a 2007 review in Motor Trend...they never explicitly say "This is a 2007 Viper," but several other sites list 2007 Viper reviews. I know the Wiki page says they don't exist, though. So, I'm at a loss here. Guess nobody would know the difference if I changed it to 2006...I'll check to see if the 06 lists for the same specs. Great catch though! Like I said, that's exactly what I'm looking for. BTW, I had to cut down the text from the book chart because it wouldn't fit in the comment window. The original chart does specify the body styles, where there are multiple styles, and where it would fit on the page.

@ Slasher: Hey man, I'm happy to have a newb reading too. Actually, I kind of need a couple...like I said, I'm trying to write so everyone from newb to vet can use the thing. Having a reader who isn't already well-versed in (or opinionated about) the subject and the science would help identify the parts that need clarification. Glad you like the idea...I've been thinking it over for a loooooong time now lol.

[Richard Rowe]

Actually, now that I think of it, I think I will post one section from the Cruising chapter here. Just so ya'll can get a feeling for my personal style, and the book's. I picked this one because it's something that you're probably familiar with, and I'm sure you know about the part I cite toward the end. Unfortunately, I can't post the cool CFD pic of airflow going around the truck...that's gonna be publisher property, and they'll pitch a hissy if they find their paid-for pics on this forum later. Text, I can work around, but those people are frickin Nazis about their pictures.

Just so you know, this particular part is first draft, and parts of it are a little darker than I go for 99 percent of the book. But, I imagine you'll understand why when you read it...especially coming from an ex-trucker like myself. But most of the book is very light and positive...this part's pretty much one of two exceptions to the rule. The other is the section on kinetic energy gains from crossing the double-yellow while cornering. That's proviso'd in pretty much the same way. Anyway...enjoy, and let me know what you think!


Drafting – Vacuum Pockets for Airheads

How good are a tractor-trailer's brakes, exactly? How quickly can a truck slow down? These days, all company trucks have computers, and those computers record everything that the truck does. How fast it's going, when it stops and where, how hard the driver brakes and even whether or not he buckled his seat belt. Trucking company safety departments use the latter two bits of information to provide the human resources department with precedent to justify random terminations free of payment for unemployment compensation. Err...sorry. That's not true at all. They use it to ensure public safety. And to win lawsuits.

Most company safety departments define a “hard braking event” as a reduction in speed of more than 7 mph in one second – a rate far within the braking threshold of the average truck. Particularly when empty. Empty, the average tractor trailer can bleed off as much as 10 to 12 mph in less than a second. So, why is this relevant information? Three reasons.

The first is that the average human reaction time, while driving, is about 1 to 1.5 seconds. The second is that, at 65 mph, you'll cover between 95 and 142 feet in that 1 to 1.5 seconds. Lastly: hitting the back of a tractor trailer 1.5 seconds after the driver slams on his brakes will have about the same effect on your windshield as driving face-first, at around 20 mph, into an 80,000-pound, horizontal, steel I-beam. And, if you're very lucky, you and your passengers will subsequently live to be dragged under that I-beam at 45 to 50 mph, inside of a screeching, burning husk of twisted steel and broken glass, by someone who didn't even notice you were there.

So...BUNNIES!!

Now, let's talk about drafting.

Truck drivers didn't invent drafting, or even discover it – but they did master it, and show the public how the technique could be of use in everyday life. You've heard the phrase “wake vortex” a couple of times throughout this chapter, and saw a brief explaination of the phenomena earlier on. But what does a wake vortex look like, and what does the drag pocket behind a vehicle have to do with it?

(PICTURE)

This is what the airflow around a vehicle looks like from above; it's what you might see if you were in a helicopter, looking down on a tractor-trailer on a foggy morning. In this picture, you can clearly see the triangular pocket of empty space behind the truck; this drag pocket is the void created when a vehicle punches through the air, and it's what's pulling you backward as you go down the road. Inside the drag pocket, airflow is almost nonexistent. Aerodynamically, any vehicle trapped within the drag pocket might as well be idling along at 5 mph.

If you look just behind the truck, you can see how a certain amount of air, sucked inward by the powerful drag pocket, will form the inward-spinning tornadoes that we call wake vortices. These vortices push anything that enters the drag pocket inward, centering it behind the lead vehicle.

Truckers figured out decades ago that getting very close to another truck made their own trucks not only somehow easier to drive – owing to the vortices' centering effect – but more fuel efficient as well. By now, you undoubtedly know why; big trucks displace a lot of air, and eliminating air resistance can free up hundreds of horsepower's worth of fuel. And the trailing truck wasn't the only beneficiary; by taking up space in the lead's drag pocket and directing the vortices down the length of his own trailer, the trailing driver relieved the lead truck of much of its own drag penalty. Start adding trucks to the line and you've got the famous, high-speed “convoy,” where all but the leading and trailing trucks run as though operating in a nearly complete vacuum.

Convoying was a big part of why truckers adopted the CB radio. A CB allowed the lead truck to communicate with his followers, letting them know well in advance if traffic and slow-downs were iminent. And drivers would typically coordinate so that the trucks were arranged from fastest and most powerful to the slowest and least powerful, heaviest to lightest, in order to avoid pile-ups while ascending and descending hills. And all of this was a necessary part of convoying, because, in order to stay in the draft, drivers had to remain no more than five to ten feet from the lead truck's bumper. And, the longer a particular trucker's hood, the closer the lead truck he had to be. Ever wonder how those flat-nosed, cab-over trucks got so popular? Or why a lot of them had huge, tube-steel front bumpers going clear up to the windshield? Now you know. Hard-core convoy truckers would often run high-double or even triple-digit speeds, packed so closely together that little nose-to-tail love taps were all but inevitable. Of course, officially, cab-overs were popular because they had short wheel-bases, and were easy to maneuver and park. But try telling that to anyone who hauled freight during the 1960s, 70s and 80s.

So, trucker trivia aside, what does any of this have to do with you? First, so you know how close you need to be to stay fully within a truck's drag pocket; 10 to 15 feet or less, depending on your speed. But primarily to point out the fact that you're probably not driving a cab-over truck, and that you almost certainly don't have a tube-steel bumper going up your windshield. And, unless you're Burt Reynolds, you don't have a CB radio. And, additionally, even if you did, any trucker worth his salt would slow down to 20 mph and stay there before he would play Front Door to a four-wheeler. So, what are you doing without that vital communications link? Driving blind at 70 mph, is what.
And, before we get to the theoretical gains, it's worth mentioning that you'll never actually be fully within the truck's drag pocket. The trailer body does most of the blocking, and the bottom of the trailer ends about four feet from the ground. At car-level, only the trailer's tandem axles run interference between you and the atmosphere, and the axle set isn't solid like the trailer box. Furthermore, the tandem axles are adjustable, and may be ten feet or more further in from the truck's rear bumper. Just something to bear in mind as you read the following, completely theoretical fuel efficiency figures.

From the earlier chart, we know that aero losses at 70 mph (the standard truck cruising speed) for the average sedan come out to around 17.6 horsepower, and losses for the average truck or SUV ring in at 35 horsepower. Assuming a BSFC of 0.40 pounds/horsepower per hour, we can calculate that the sedan would save about 7 pounds of fuel per hour, and the truck/SUV would save around 14 pounds per hour. As a US gallon of fuel rings in at about 6 pounds per gallon, that's 1.12 gallons per hour saved for the car, and 2.33 gallons per hour for the SUV. Assuming that the car started out at 30 mpg and the SUV at 18 mpg, and converting gallons/hour to miles per gallon, we get...

56 mpg for the car, and 47 mpg for the SUV.

So, are those figures realistic? Possibly not, since they assume that the trailing vehicle is operating in a complete vacuum. Which it isn't quite, given airflow around and over the tandem axles. But, even if you're feeling pessimistic and want to subtract 20 percent for airflow over and through the tandem axles, this calculation still yields a 52 percent increase in fuel economy for the car, and a whopping 208 percent increase for the aero-challeneged SUV.

Now, do those numbers reflect real-world testing? Yes, they do. And then some. Back in 2007, the Discovery Channel's Mythbusters infamously performed this test using a Dodge Magnum (baseline 32 miles per gallon) and a Freightliner at 55 mph. At 10 feet from the truck's rear bumper, the Magnum's fuel economy jumped by a full 40 percent. But, you say, 40 percent isn't 52 percent. True, Grasshopper – but recall that the Discovery Channel performed its test at 55 mph, and our calculations assumed 70 mph. Given the difference in power consumption between 55 and 70 mph (about 10 horsepower for the car, and 20 horses for the SUV), it's almost certain that, at 70 mph, the blunt-nosed Magnum would have seen efficiency gains handily exceeding our fudge-factored 52 percent, and possibly very close to the original, theoretical 86 percent.

So, does drafting save gas? Yes it does, without a shadow of a doubt. Does that mean you should do it? You can if you'd like. But please don't have children before you do. First, because you don't want to leave kids to face this world without a parent. And second, because Social Darwinism suggests that they'd only wind up spawning a race of hairy-palmed Morlocks.

[JRMichler]

I'd like to see what you have to say about DWL and DWB, because that's where most of my MPG gains came from.

[jamesqf]

Re the drafting chapter, I do think you need to get into real-world traffic spacing, especially on e.g. California freeways. (Presumably elsewhere, but my personal experience is Northern California, & Northern Nevada in what passes for heavy traffic hereabouts.) The plain fact is, you're going to be spending the majority of your time a couple of car lengths from someone's rear bumper, 'cause if you try to leave more space, someone else will cut in.

That being the case, I think I'd rather be behind a semi with one of those nice bars designed to prevent rear-enders from going under, than just about anything else I can think of.

[Richard Rowe]

Hey man...yeah, there are pretty extensive sections in the book on driving without brakes and driving under load. The braking chapter started out as one of the shortest, since, really, what else is there to say besides "Don't use them?" Eventually though, I wound up expanding it to cover situations where you HAVE to brake (red lights, traffic, ect) and how to identify and avoid those situations.

Far as driving under load goes, I found that it depends on the engine, vehicle and transmission. The difference in BSFC under full-load (100%) vs part-load (25%) is generally the greatest at really high and really low rpm...the two are pretty close to equal right around peak torque. So, as long as you're within a couple hundred rpm of peak torque, then it doesn't matter as much if you're under full- or part-load.

But, all else being equal, power production and use is ultimately the deciding factor. The amount of airflow (throttle) going into the engine determines how many horsepower you're making, and BSFC determines how efficient those horses are. So, you don't necessarily stand to gain anything if you cut BSFC in half by loading the engine, but have to double airflow to do it. It's a balancing act. I've found that driving by load seems to work best on engines that have a really high torque peak (where BSFC is about equal regardless of load) that you never see under cruise conditions with your vehicle's gearing. In cases like that, yeah, it generally makes sense to trade off some extra airflow for an increased BSFC.

That logic would seem to stand up pretty well in your case, since even the LH8 5.3-liter in the GMC Canyon hits peak torque at 4,000 rpm, and the inline-five peaks at 4,600. Weirdly (or maybe not) the four cylinder peaks at 2,800, so it would seem to be a little less sensitive in terms of driving under load. BUT (and understand I haven't seen a dyno sheet for any of these), my guess is that the four-cylinder's torque and BSFC drops off a lot faster than either of the bigger engines...so, there's a good chance that it would work better going by load at low rpm. And considering your mileage, I'm guessing you have the four cylinder.

The only way to know for sure would be to find a BSFC @ load graph for your engine. The bigger the difference in load-variable-BSFC at a given rpm, the better off you are going by load. Of course, those charts are kind of hard to come by...I had to do some hunting to find a few for the book, and those were just for random engines of different types. But, a typical BSFC chart (measured at 100 percent load) will give you some idea as to how quickly it drops off on either side of peak torque. Generally speaking, the quicker it drops off, the more sensitive your truck is to load.

Just a little aside: I used to have an '85 Mercury Cougar with a 500 Caddy engine that I called my "12 mpg car." It got 12 mpg, no matter what you did to it, where you drove it or (for the most part) how you drove it. I didn't understand it at the time, but now I know it's because, with that car's gearing and the 500's table-flat torque curve, it never really strayed far from BSFC under full load. Which was good, because it didn't exactly stay under full load for long (when it did). So, as long as you didn't rev the hell out of the thing, it pretty much got the same fuel economy all the time. But that car was horrifically overpowered, and stripped down to about 2,800 lbs even with the Caddy engine. So it didn't care what you did. Your truck (assuming it has the four cylinder) is just the opposite.

And that's my thought on that

(PS: Approaches change depending on whether you have a manual or automatic. DWL works best for the manual because you can vary load by changing gears yourself. With an automatic, you're better off driving by the vacuum gauge once you're under way.)

[redpoint5]

Originally Posted by Richard Rowe

But please don't have children before you do. First, because you don't want to leave kids to face this world without a parent. And second, because Social Darwinism suggests that they'd only wind up spawning a race of hairy-palmed Morlocks.

Not sure this writing style is best suited for the masses, but I LOLed! The humor makes a good point while keeping the tone light.

Does the section go on to explain drafting at longer following distances? It's doubtful anyone here is drafting at 10ft behind a tractor/trailer, but there has been discussion of the benefits of close-following behind one. I don't recall exactly what I read, but there may be benefits to following even as far as 120ft?

I'd be interested in providing feedback for the book. Sounds like a very good idea, and I'm surprised it hasn't really been done for the layperson before.

[Richard Rowe]

James SQF: Sorry about that...I didn't see your post when I replied. As far as traffic spacing goes, I did address that elsewhere in the book when I talked about following distances. My opinion on people cutting in is, and pretty well remains...so what? What's going to happen then? You'll need to back off to increase following distance, then another car will cut in. Back off more, and another car cuts in. So, your average speed winds up slightly lower than most other cars...but what else is new lol? I mean, I doubt anyone who's serious about hypermiling isn't familiar with the concept of getting passed.

At some point, you will reach an equilibrium speed where people are going so much faster than you that you don't have to slow down to increase folling distance...in my experience, 5 to 8 mph below the traffic speed. Obviously, that threshold rises or falls with traffic speed and spacing, but it does come at some point. So, personally, I don't treat traffic any differently than I would anywhere else...you're going to go slower than average. That's just the nature of the beast. I figure that sooner or later, I'll make up the time by not stopping for gas. Might only be once a week, but one 15-minute gas stop still subtracts 5 mph on average from a 100-mile weekly commute at 50 mph. So...meh.

However, I did mention in the braking chapter a bit about light timing. All of this is only true if you catch the same number of lights as the other drivers. Catch one more light, and you might have just shot your FE savings. So, considering that most places that time lights time them at 5 mph under the speed limit, that's the practical threshold for going slower than traffic. Faster, you're wasting gas...slower, you're idling at stoplights.

Redpoint5: lol...Yeah, well...it's been my experience that that the masses usually like stuff that they think the masses wouldn't like. Personally, I'm more worried about appealing to my own, younger generation than I am older ones. There are a lot of little pop culture and internet references in the book along those lines. I think I even used the word "lol'd" at one point. So, as long as you liked it, then that's all that matters to me

As far as the following distances in drafting go: yup. You're right, and no, I didn't get into it. Just going from the Mythbusters test, I believe there was a 26 percent improvement at 100 feet. I was playing with the idea of mentioning it, but I'm kind of avoiding it for a couple of reasons. 1) I wouldn't even have talked about drafting, if it weren't just due process, and 2) since the average person would even react to the truck stopping at 100 feet until 4 feet before they hit it, I thought that might just be setting them up for a harder impact if they are dumb enough to draft. Hit a truck from ten feet away after it brakes, and the speed difference between you and the truck is maybe 5 mph. Hit it from 100 feet (when the truck has had longer to slow down) and the speed differential might be 20 mph or more.

So, if you're going to be close enough to the truck that you'll hit it no matter what, you're better off riding two feet from its bumper than you are 100 feet. So, you can probably see why I didn't get into the distance thing. I'm all for due process and all, but there's no sense in offering any more encouragement than necessary. Know what I mean?

And, yep, that surprised me too...you'd think someone would have done something like this before now. But everything on the shelves along the same lines has at least one calculus equation in it, and they read like encyclopedias. Even I had trouble not nodding off for some of them. Probably the only reason that I'm not the same way is that this stuff has always been a hobby for me...I never went to school for engineering, aeronautics or any of that. I just read a lot. And, I work alone. But if I had professors, students or co-workers to impress, it probably would have turned out the same way. Ahhh, vanity...my favorite sin

[Vman455]

Originally Posted by Richard Rowe

@ Vman455: See, that's EXACTLY what I'm looking for. But (and understand I'm not arguing here), weren't the late 2006 models released as 2007 models? I pulled the Viper Stats from a 2007 review in Motor Trend...they never explicitly say "This is a 2007 Viper," but several other sites list 2007 Viper reviews. I know the Wiki page says they don't exist, though. So, I'm at a loss here. Guess nobody would know the difference if I changed it to 2006...I'll check to see if the 06 lists for the same specs. Great catch though! Like I said, that's exactly what I'm looking for. BTW, I had to cut down the text from the book chart because it wouldn't fit in the comment window. The original chart does specify the body styles, where there are multiple styles, and where it would fit on the page.

I'd be happy (and interested) to read more! Nope, no 2007 models--2006 production was extended through December (when it normally would have switched over in September), and the 08s began production in January 2007. I would go back to whatever source you got the Cd number and try to determine whether it was for a 2006 or 2008. There was one difference in the body design: the hood of the later cars had much larger vents which may have had an effect on Cd as it exhausted engine compartment air.

2006 hood:



2008 hood: