Talk:Energy-efficient driving/Archive 2

coasting out of gear
The whole discussion of coasting out of gear should be moved out of the accel section, into its own subsection under specialized techniques.Ccrrccrr (talk) 12:51, 19 February 2008 (UTC) - It's also loaded with speculative opinion: "has the added safety benefit of being able to react in any sudden change in a potential dangerous traffic situation, and being in the right gear when acceleration is required.[24]" -- the alleged 'safety benefit' is never substantiated, no imaginable scenario where such sudden acceleration would be required is described (nor can I think of one), and even if it could be, the vehicle would not be in "the right gear" for acceleration but by definition would be in a lower gear requiring a quick change to a higher gear anyway, so ultimately the point contradicts itself. — Preceding unsigned comment added by 50.55.95.219 (talk) 16:29, 20 July 2012 (UTC)
 * Not sure what you mean in parts here. Whilst I agree that it's speculative, there are many circumstances where acceleration may be unexpectedly needed - should a vehicle approach from behind excessively fast, or when you need a boost to beat the lights, calculating that the extra fuel used to accelerate is less than the fuel used idling at the red light, and then re-accelerating back to cruising speed - to name but two examples.  Kind of agree about the comment about being in the "correct" gear - it might be more accurate to say "in gear" instead of "in the correct gear".  Also don't know what you mean "by definition would be in a lower gear requiring a quick change to a higher gear", as lower gears offer better acceleration than higher gears.  Do you mean  "by definition would be in a higher gear requiring a quick change to a lower gear"  Still, it's all ambiguous.  Chaheel Riens (talk) 17:50, 20 July 2012 (UTC)

(response) Neither of those two examples of acceleration is a legitimate safety concern; in (a) your stated course of action is not a given, and even if it is the chosen course of action, since the vehicle is in motion the same direction as the approaching one, it isn't a "sudden" enough situation to be affected by whether the car is in gear or not. Same with the stationary object in (b); traffic lights are timed and predictable. Neither of those scenaria describe "sudden". That's why it's hard to think of an example; they really don't exist in the wrong direction. A sudden change to the motion of a vehicle engaged in the act of going West lies westward, in the future, not eastward in the past. On the point about gearing: if a vehicle is coasting in gear (presumably downhill) then the gear selected is running fairly high in the range of that gear in order to engine-brake (otherwise it would be lugging); to accelerate from that point requires revving even higher, or shifting to a higher gear for proper torque, which would have to be selected pretty soon anyway -- ergo a shift to a higher gear is required regardless whether the vehicle was in gear at the start or not; ergo there's no advantage or disadvantage in being in or out of gear (IOW it wasn't in "the right gear" for acceleration; it was in the gear below the right gear). The passage is basically an extreme stretch of logic to make its preachy one-sided point and I agree the whole section is ambiguous, and full of opinionated writing. The entire page suffers from failure of NPOV (as the length of this talk page attests) and should possibly be scrapped and completely reworked.


 * Sorry, but I disagree. Both examples are perfectly valid representations of when speed is required, and if you are moving slowly, and a vehicle comes up behind you quickly, then yes, a sudden burst of speed is required, ergo argument criteria met.  Also, you are changing the goalposts - the statement does not say that "sudden" acceleration is required, only "when acceleration is required".
 * I still don't understand your argument about being in the wrong gear. Do you mean that when you coast in gear, you have the transmission in a low gear, so the engine is high revving?  Your arguments are counter to each other - an engine generally reaches maximum torque at a high range, which you seem to be suggesting you are already in.  If you change to a higher gear your revs will drop and the torque will also drop.  Just as you cannot see my argument, I cannot see any possible scenario which would have you in a high rev band, and then need to change up a gear to generate sufficient torque for acceleration.  (Although I'll admit you could mean that you are redlining the engine, in which case yes, you'd need to change up, not only for acceleration, but before your engine exploded - fuel cutoff or not.)  And as a side note - being in a high rev band is anathema to a hypermiler philosophy, regardless of whetehr coasting or not - even under no load the engine is still whizzing round putting wear & tear and strain on the components.  A Hypermiler would use high gear/low revs and gain momentum under coasting and (engine)brake only when necesseary.  Chaheel Riens (talk) 18:40, 24 July 2012 (UTC)

Don't move to wikibooks
This article was prefaced by the form statement proposing to move the article to wikibooks. I deleted this because it's now more like an encylopedic article than what is supposed to be acceptable to wikibooks. Since the wikibooks proposal was added, this article has been improved by deleting Auto-stop, finding more quality citations (including a Ph.D. thesis), and explaining why "pulse and glide" works. Much of this was done by me, David S. Lawyer.66.81.123.41 (talk) 17:31, 27 September 2012 (UTC)

Tripcomputer a luxury option?
I think the information is very outdated. All cars I've driven or friends have driven have at least a option to show the trip mileage. Most also have the option to how the current mileage. I wouldn't really call a '01 Mazda Premacy or a '99 Toyota Vitz or a '05 VW Polo a luxury vehicle. SkySilver (talk) 19:58, 13 October 2012 (UTC)

Time to cut the jargon
There is at least one section here that promotes the terminology promoted by one sleb wannabe. They aren't in general use. I suggest we remove the section 2.2.3 Auto-stop, forced stop, and draft-assisted forced stop Greglocock (talk) 10:28, 19 April 2012 (UTC)
 * I agree and a month ago I deleted this stuff. David S. Lawyer 07:04, 26 October 2012 (UTC)

Name changes: "... behaviors" to "Maximization ..." to "Energy ..."
On Oct. 2, 2012, Thumperwald changed the name of this article from "Fuel economy maximizing behaviors" to "Maximization of fuel economy". Then on Oct. 28, 2012, I (David Lawyer) changed it to "Energy-efficient driving". I claimed that the change made by Thumperwald was not right. There was no discussion of Thumperwald's change. The new "Maximization ..." title greatly broadened the scope of this article. Design of automobiles and their components such as engines, transmissions, body aerodynamics, etc. all may be used to help maximize economy, but this article was intended to cover only how driving techniques (behaviors) can improve fuel economy. If this article is to get into the details of motor vehicle design, then it would need to consider not only fuel economy, but costs, safety, etc. since there are tradeoffs. And this would amount to a big expansion of the article's scope which I don't think should be undertaken. I originally proposed (on 26 Oct., this talk) to, for the time being, revert to the old name, which does seem a little awkward. Then I suggested "Fuel efficient driving". But then after thinking about it I thought "Energy-efficient driving" would be better since it would include electric vehicles. So I've changed it. Discussion is welcome and I'll go along with any consensus reached regarding what the name of this article should be. David S. Lawyer 23:37, 28 October 2012 (UTC)

wrong info regarding 2004 impala
I was reading over the sources and 2004 impala's course is no source at all. there is nothing on that entire powerpoint that states this "70km/h" the graph has nothing to do with anything. — Preceding unsigned comment added by 129.97.175.37 (talk) 22:44, 12 September 2013 (UTC)

reference to a specific engine but engine is not specified anywhere
"The optimum efficiency point is around 1750 rpm, and 90% of maximum torque at that speed, for this turbo-diesel engine."

"this turbo-diesel engine" is not referenced anywhere. This has ether been lazily copied from somewhere or someone has forgot to include the name of the engine they are referring to.

A Google search would indicate this has been copied from a website which is itself a copy from another website. attempting to track down the original was fruitless as the original article seems to have disappeared.

80.5.128.19 (talk) 15:52, 4 June 2014 (UTC)


 * You're absolutely correct. I've removed the references to the specific engine as it cannot be corroborated.  Apologies for taking so long to do so.  Chaheel Riens (talk) 12:47, 12 August 2014 (UTC)

Optimum speed depends on whether you're on your way somewhere or not
If you're driving for fun 35 mph might be the optimum speed (for some cars, see the article) but if you're on your way somewhere it tends to be about 50 mph. That's because saving for example 10% fuel by driving 35 mph doesn't help if you have 20% of the trip left compared to a car that's driving about 50 mph and reached already its destination. — Preceding unsigned comment added by 84.248.20.195 (talk) 11:50, 12 August 2014 (UTC)
 * This article is about maximizing fuel economy. It's pretty clear that that is what the whole point is, not when you need to be someplace.  Side note: for most cars the optimum speed is when you just shift into top gear. This article says "35 or 50", should be "between 35 and 50", I'll correct that. Nerfer (talk) 22:39, 5 November 2015 (UTC)

Experiments require explanations of what was done (how-tos)
The label "This article contains instructions, advice, or how-to content (September' 2009)" was applied to this article. Yes, it does contain such content but this content can't be removed since the article is intended to be a scientific analysis of the results (better energy-efficiency) of experiments. Thus a description of the experiments includes a detailed description of of what was done (how the car was driven) and this is in effect certain instructions and advice (how-to). These are certain control polices (instructions) used for control of a physical system (a motorized vehicle).

One can also analyze Pulse-and-Glide by using Optimal Control theory. It's been done for railroads but not for automobiles. I've done some of this for railroads but haven't published it. The result I derived is known as a Bang-bang control policy, which is exactly what Pulse and Glide is. It's a shame that the Ph.D. thesis on pulse and glide didn't analyze it from the standpoint of Optimal Control. One impediment to applying such theory is that the Brake specific fuel consumption curves are often kept secret. David S. Lawyer 01:27, 19 November 2013 (UTC)


 * Check out Peter Pudney's work on railroad fuel economy. Actually this entire article is so banal it shoud be deleted. BSFC curves are not really secret, they just aren't published usually, and at least in the case of cars, aren't the whole story Greglocock (talk) 09:36, 19 November 2013 (UTC)


 * I removed the labels as several large edits have occurred in the years since they were tagged, and didn't seem relevant any longer. They can be addressed on a line-by-line basis if needed (and there are a couple claims that are tagged with 'citation needed'), but not a systemic statement. Nerfer (talk) 23:07, 5 November 2015 (UTC)

recent massive edits removed important info, restructure?
You go guys/gals/aliens/wikipedians, and don't be afraid to restructure the entire article, most of it is a holdover from fatuous self promotion tautologically by a self promoter. In fact, should we start a discussion of a sensible structure? Cheers Greglocock (talk) 10:14, 19 February 2015 (UTC)
 * I've thought a little about this as I've worked on the article. It's still a bit of a lumbering beast--and it's hard to work out what it's trying to talk about--Maybe we could head towards it being "an encyclopedic article about how human behaviour affects fuel economy". This would help minimize the big overlap with Fuel economy in automobiles and Fuel efficiency.
 * I have mostly used the article as copyediting practice, so I've attacked content in the small. Perhaps an easy next step might be to find content duplicated in other articles and (on the probably-true assumption that this article's content is worse) delete it. That would help this article find its niche a bit better. tommylommykins (talk) 19:04, 21 April 2015 (UTC)


 * OTOH, pulse and glide, hypermiling, and probably other terms are redirected to this article, even though it doesn't even describe those terms. So we need to fix up this article.  Some people have deep-set beliefs on the subject, and it might get contentious at times. Nerfer (talk) 23:00, 5 November 2015 (UTC)


 * "Pulse and glide" (P&G) and "Drafting" were not removed by these massive edits. But they were removed by later massive edits which I first thought was vandalism for the case of P&G.  But now I'm beginning to think that the person removing them was likely  misinformed on the subgect and thought that P&G hadn't been proven to be effective.  But much of the "Drafting" section that was deleted was nothing more than repeated warnings about how dangerous it supposedly is.  This part deserved deletion but the rest of the section should have been kept.  I added the word "vandalism" to the heading of this talk section and later deleted it.  Today I manually restored P&G and "Drafting" but I recall that "Drafting" was once longer than what I restored).   Pulse and glide really works and a PhD thesis about it (on the Inet) was one of the deleted references.  This got restored too, not by me but by an "orphaned references bot" which found deleted references and restored them since references in the deleted text had used the "ref name" format.   BSFC maps which contain a road load curve shows how P&G works.  Unfortunately the Wikipedia BSFC map is for a Diesel for which Pulse and Glide is less effective and it fails to show a road-load curve (a plot of torque vs. rpm at steady speed on a level road}.  There are now a few good BSFC maps on the Inet.


 * One topic that was once covered better was drafting (driving closely behind a large truck or other large vehicle). It may have been deleted in the first series of massive deletions.  Someone on the Inet claimed they drafted behind a large truck (with permission) on a motorcycle and that most of the time the suction was such that no power was required at all.  While Pulse and Glide is a well established fact (based on BSFC maps) drafting in the case of no fuel consumption is problematical and may not belong in Wikipedia.  But drafting does belong in Wikipedia (perhaps in its own article on drafting).David S. Lawyer 08:53, 21 November 2015 (UTC)


 * Refs get removed if they aren't used in the article. That's a fact of life. If you've got a ref for P&G put it in. Yes I know it works. However I suspect an explanation of how it works would be considered OR, unless it paraphrased an RS. The maths is quite complicated if it is right, and the usual approximations that people make are misleading at worst, inaccurate at best. Greglocock (talk) 09:02, 21 November 2015 (UTC)


 * The above was written before I went over my 21 Nov. post later on and edited it a couple of times. I've now started a new section in this talk on P&G.  I think it's possible to give a good explanation in Wikipedia on how it works.  I'm now editing the Rate (mathematics) article to show how to take weighted averages of rates (such as thermal efficiency, a dimensionless rate used in P&G calculations) including what weights to use.  I also need a good BSFC map for gasoline engines which is free to put in Wikipedia.  Using a BSFC map explains P&G but doesn't explain why the map is like it is.  But if one accepts that the P&G map, (based on experiment and not on theory) is correct, then P&G is easy to understand.

P&G criticism
"Coasting is most efficient when the engine is not running, although some gains can be realized with the engine on (to maintain power to brakes, steering and ancillaries) and the vehicle in neutral, or even with the vehicle remaining in gear.[24] Most modern petrol vehicles cut off the fuel supply completely when coasting (over-running) in gear, although the moving engine adds considerable frictional drag and speed is lost more quickly than with the engine declutched from the drivetrain."

Not being able to see the ref that phrase in bold strikes me as borderline ludicrous at least for real conventional cars. I think we need a ref that people can see and judge for themselves. It sounds like an outcome of poor modelling or very special circumstances. Figure 3.10 in the Jeongwoo_Lee paper shows why, leaving it in gear results in a deceleration 3 to 6 times that in neutral. Greglocock (talk) 22:40, 6 December 2015 (UTC)

http://scholar.lib.vt.edu/theses/available/etd-09172009-234744/unrestricted/ETD_PhD_Dissertation_Jeongwoo_Lee.pdf figure 4.5 assumes a fuel flow rate of zero when the vehicle is coasting. that implies the engine is off, which means we are no longer in Kansas. I can imagine smug little gits driving along the freeway switching their engine on and off every 40 seconds. I can also imagine them being wiped off the face of the earth when one of several things happens. Incidentally that PhD is a fail in my book, a bit of stuffing around with a simple computer mode and no actual complex maths means the guy doesn't understand anything particularly new, the level of maths is high school. Greglocock (talk) 22:40, 6 December 2015 (UTC)


 * Having flicked through the ref I see no suggestion that supports the statement in bold. Greglocock (talk) 04:30, 7 December 2015 (UTC)

More Stupidity - 400W
"The National Renewable Energy Laboratory in a 2000 report suggest that a 400 W load on a conventional engine can decrease the fuel efficiency by up to 20%.[4]"

Well i'm sure it does, especially if the engine is producing about 2000W or less, ie idling. So what? The given reference does not support that statement. Greglocock (talk) 10:43, 7 December 2015 (UTC)

Pulse and Glide (P&G)
These sections were deleted on 1 May 2015 and manually restored by me today (24 Nov. 2015). There's a newer thesis on this topic by Jansen that need to be better incorporated into these sections P&G needs to be integrated into the rest of the article and at present, it seems to be just a note tacked onto the article as an afterthought. I hope to find time to work on this. It turns out that it is not optimal to just travel at steady speed and P&G (Pulse and Glide) illustrates this. Thus the implication that steady speed is most efficient needs correcting. On a road with long up and downgrades, one can use the equivalent of P&G by driving uphill (efficient since the torque is high) and then coast down the following downgrade. The pulse is the uphill part (a long pulse) and the glide is coasting downhill. A few years ago I wrote an article on P&G and placed it on my website: | Case for coasting. This article is more like a How_to and I use a lot of "you's" so it doesn't fit in with Wikipedia style, except it does contain more technical information that needs to be put into Wikipedia (with more reference). David S. Lawyer 05:52, 22 November 2015 (UTC)David S. Lawyer 08:10, 24 November 2015 (UTC)David S. Lawyer 08:14, 14 December 2015 (UTC)

Some ideas to include
The fellow who modified his Honda civic and is reportedly getting 100-120mpg seems to be notable (http://www.aerocivic.com).


 * This doesn't belong here because it is about vehicle design and modification and not about driving techniques.David S. Lawyer 08:53, 14 December 2015 (UTC)

The people who are helping honda insight owners take full control over their electric assist (MIMA) are interesting. (http://99mpg.com/mima/mimaintroduction/) They are selling a joystick that allows you to drive your hybrid and control when it charges and assists.Chickpecking (talk) 03:14, 6 December 2015 (UTC)
 * Unfortunately, this doesn't explain how to use the BSFC curves in maximizing efficiency.  One should often run the engine at high torque and low MPG so as to increase engine efficiency, storing much of this energy as potential or kinetic energy (similar to P&G).  However, there's a big loss in charge-discharge cycles - not only battery losses but electric motor-generator losses so it's best to avoid much of the battery charging if possible.  I think this article fails to cover the topic of MIMA very well.David S. Lawyer 08:53, 14 December 2015 (UTC)

Drafting using no fuel
There once was a mention in this article of a claim that a motorcyclist drafted behind a truck for hours and most of the time just "coasted". This coasting must have meant that the aerodynamic drag on the motorcycle was negative, and that the wake of the truck provides enough forward thrust to overcome the rolling resistance of the motorcycle. Is this feasible? In it shows the drag coefficients of two cylinders of equal diameter, the first cylinder shielding the second from the wind. It turns out that for close spacing (the second cylinder being approximately less than one cylinder diameter behind the first (leading) cylinder, the drag coefficient is negative (the aerodynamic drag is reduced by about 130%). That is, the wake of the first cylinder creates a forward aerodynamic thrust on the second cylinder, pushing it in a direction opposite to the wind.  This experiment is like the second cylinder was "drafting" behind the leading cylinder.  Somewhat similar results are shown for two circular disks, one behind the other (but the induced thrust isn't as pronounced).

The above result tends to support the feasibility (in some cases) of drafting without applying any motor-driven thrust to the drafting motor vehicle. Another question is that of stability. If the induced thrust (due to the negative drag coefficient) increases the closer the drafting vehicle gets to the "truck" (leading vehicle) then the vehicle behind the truck might accidentally crash into it. But it turns out that for the cylinders, there is a stable zone about 1.7 diameters behind the leading cylinder. If motor vehicles behaved similar to cylinders then for drafting behind a truck: move closed to the truck and the drag goes positive, tending to push the drafter back away from the truck. And conversely, should the drafter move back further away from the truck the drag coefficient goes negative, providing forward thrust. But perhaps not strong enough negative to overcome rolling resistance. When the trailing cylinder is close to the leading cylinder (within 1/2 of the cylinder diameter) the negative drag (per the curve in ref. 1) stays nearly constant. However, there are not enough data points in this region to accurately determine the shape of this curve so the negative drag may not actually be constant in this region and a stable situation might exist.

Of course the above results don't prove that no-fuel drafting is feasible, but indicate that it might be. Additional wind tunnel testing would be of interest to resolve (if only partially) this question. Has anyone done this? David S. Lawyer 07:52, 14 December 2015. David S. Lawyer 18:58, 14 December 2015 (UTC)