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Fuel Consumption at Higher Speeds

Autobild1
Auto Bild test data for 8 of the cars, rendered as fuel economy (mpg US) rather than fuel consumption (l/100km). Click to enlarge.

While it may seem intuitive that driving at higher speeds consumes more fuel, exact data on just how much a difference that makes model-by-model isn’t readily available. The editors at the German weekly Auto Bild recently changed that, however, publishing (12 May 2006) a head-to-head comparison of the fuel consumption of 16 different models of cars under higher speed driving conditions.

Testing was done at the Automotive Testing Papenburg (ATP) 12.5 km high-speed circuit in Germany. The editors measured fuel consumption using on-board computers at speeds of 80, 100, 130, 150, 180, 200, 220, 250 km/h and at top speed.

The guzzler of guzzlers was the Porsche Cayenne Turbo S, which swills down an eye-popping 66.7 liters of fuel per 100 km at a top speed of 270 km/h—that’s 3.5 mpg US at 168 mph. Of more prosaic interest was the difference in performance between diesel and gasoline versions of the same cars, as well as some data gathered on the difference a bicycle carrier on the roof can make, or driving with the top down.

Autobild3 Autobild4 Autobild5
BMW 5 series diesel and gasoline. Click to enlarge. The downsized VW twin-charged TSI vs the larger diesel. Click to enlarge. GM Opel Zafiras. Click to enlarge.
Prius data is included on each chart as a reference.

Adding a rooftop bicycle carrier to the BMW 530i Touring model increased fuel consumption by 11% at 100 km/h (62 mph). That gap increased to 26% at 180 km/h (112 mph).

Driving a Mercedes SLK 200 K with the top off imposed a 5.8% penalty on fuel consumption at 100 km/h.

(A hat-tip to George Minko!)

Comments

LOL

WOW the Prius gets really poor fuel economy. I trust these numbers over any of the claims I read in these comments. I guess that car is all hype after all. Give me a diesel. Thanks for converting all the figures by the way.

Robert Schwartz

And at 0 mph, your milage is 0 mpg. My Accord gets 30 mpg on the highway, and I don't drive 65.

Joseph Willemssen

The point isn't the exact data but the trend lines. It's nice to see a demonstration of how steep the drop-off is for fuel economy as speed increases, no matter the vehicle.

Eric S. Johansson

odograph wrote """Eric S. Johansson, you completely disregard the cost of the additional gas burned(at lower mpg), the additional emissions generated, and the additional risk of accident at faster speeds. Go ahead enjoy 3 more minutes of American Idol. BTW at GCC we value time min. $100/hr"""

if I had written out the full model of cost of transport I would have included the factors you have pointed out with the end result of shrinking the difference between the cost of transportation by different modes.

my unfortunately incomplete argument was that economics beyond the cost of energy drive consumer behavior. Yes, higher price of gasoline will drive people to alternative fuels, not because it's the right thing to do, but because it's cheaper and only because it's cheaper. I was trying to outline some of the alternative factors that come into play when people behave the way they do.

people drive fast because it saves them time (or, if they're like me, they enjoy the speed. It's really pleasant driving down the highway at 80 miles an hour. I don't know why, it just is and I love my golf.)

as for the accident issue, accidents happen when a driver exceeds the limits of the roadway surface, their skill, and vehicle maintenance. Another huge factor is speed differential. If you have a highway where everyone is traveling 80 miles an hour, you'll have less accidents than one where people are driving 55 and one lane and 80 in another. A third factor is aggressive driving. If you drive fast and swerve through lanes to keep your speed up, that's an accident in progress. If on the other hand you travel fast but not aggressively, you are at less risk to accidents.

if memory serves accident statistics indicate a vast majority of actions take place on secondary roads were the speed limit is under 45 miles an hour. I swear, people just don't know how to drive if it isn't just straightahead.

for the record, my wife and I have six accidents between us with 70 years aggregate driving time. The fastest was 30 miles an hour, three of them were in a dead stop when somebody else backed into me, twice when I was not even in the car.

on $60 per hour, I chose that rate as a reasonable lower bound worst-case. Yes, $100 an hour is a much more realistic average but I was trying to degrade the model to see how it works at the lower end.

and please, if you must get snitty, don't make comments about American Idol. Those poor people suffer enough (voluntary) humiliation as is. Please direct that energy towards organizations like heifer Project or Habitat for Humanity if you must direct it anywhere.

odograph

I'm worried that the nature of the test (oval track) compresses the cars into similar 80 mph fuel economies, when there would be a greater distribution real-world.

People might say "hey, if I'm going to go 80, I might as well get a 535 BMW."

.. who did this study again? ;-)

odograph

Erc S. Johansson ... please figure out where the author's name is on each post.

fyi CO2

"for the record, my wife and I have six accidents between us with 70 years aggregate driving time. The fastest was 30 miles an hour, three of them were in a dead stop when somebody else backed into me, twice when I was not even in the car."

Based on your experience/rationale, to avoid any future accident, you should never drive less than 30 mph.
PS: you won't find many of the people that get in an auto accident driving 80+ mph on this site, or any site for that matter.

Chingy

All right, am I confused or are most of you confused? Isn't the point of this study to compare vehicles, under identical driving conditions, which also happen to be at high speed? If so, you Prius people should relax a bit, of course this test will not be in line with what you get on the interstate. But, it does a perfect job of comparing vehicles under identical driving conditions.

I am assuming here, but I say if you take a TDI Golf or Jetta and drive it your way, you'll still find it beats the Prius hands down. Look, your Prius is a nice baby step, its getting the public acclimated to more efficient designs. BUT, it ain't the be-all-to-end-all. Diesel electric...no reason it should not be in the Prius now. Plug-in capability...ditto. Diesel-electric-plug-in... can you say 200mpg, burning biodiesel, while still driving like a dumb-ass teenager? :)

Joseph Willemssen

I am assuming here, but I say if you take a TDI Golf or Jetta and drive it your way, you'll still find it beats the Prius hands down.

Contrary to both EPA estimates and real-world data, and of course you again ignore the vast differences in emissions.

And, no, I am not going to debate this with you again. The Prius is cleaner and more efficient than the TDIs. You do your preference a disservice by claiming otherwise.

Let's let the new cleaner diesel technology start filtering in the next couple years, then let's see where things stand then. By that time the next generation Prius should be out, as well.

Wayne

Just for fun I have done the following workup against a Prius Energy Use Simulator.

The first graph at the top of this article shows the following data points for the Prius.

MPH.....MPG
45......48
60......37
80......30
105.....20

I set up the Prius Simulator with variables as can be seen at:

http://privatenrg.com/Papenburg.htm


Pretty much a normal 72 ºF day against an OEM 2004 Prius. No elevated tire pressures & etc… All OEM & here is the table I got against the same speeds:

MPH......MPG
45......66.75
60......56.48
80......42.51
105.....28.52

Something is drastically incorrect about this article's data.

In order to get anything close to what the article shows, I had to add an 18 MPH crosswind coming at the Prius 31º off the Prius’ heading (the worst kind of headwind – crosswind angle there is for the Prius) & I got the following table.

18 MPH CROSSWIND 31º OFF PRIUS' HEADING
MPH......MPG
45......48.06
60......39.64
80......29.64
105.....20.09


I checked the weather in Papenburg today & they are having 19 MPH winds out of the SSW so, maybe the author(s), editors & publishers of this data all forgot to include some pretty important information like a big crosswind.

Screenshots of the exact variables used in the simulator & amounts of power in kilowatts & horsepower all divided up against Aerodynamics, Mechanical, Tire & Road Rolling Resistances & much more for the above tables can be found at:

http://privatenrg.com/Papenburg.htm

Best Regards,
Wayne

Chingy

Joe, who mentioned anything about emissions? This post is simply about fuel consumption. Seems every real world test that comes out shows the TDI beating the Prius, how do you explain that? Come to think of it, wasn't this post solely about fuel consumption at high speeds?

Eric S. Johansson

odograph: if I got attributes wrong, I apologize. The exceedingly poor human factors of web forums/blogs makes it difficult to do the right thing.

To my eyes, each comment is in a box bounded above and below by horizontal lines. The poster is inside the top followed by the comment. but on closer examination, thanks to your comment, I see the straightforward and obvious interpretation of the information presentation is wrong.

The developer of this format is either very dim, or exceedingly ignorant of typographic convention going back hundreds of years. They really need to read Tufte's books on information presentation.

again, I apologize for getting the attribution wrong.

George

Chingy, Check the title of this blog again. You like diesels, fine. If you can find a place to drive them that doesn't poison the rest of us with particulates, then drive them there. In the meanwhile, until diesel technology that solves the particulate problem is standard, I can't consider them as a solution. I would rather have a nuclear power plant in my backyard than have everyone driving diesels.

Chingy

George, I don't "like" diesels. I simply understand that they are the best way to go for the time being. I truly "love" EVs, and plan to build my own this year. As for your polluting comment, you should have stopped before mentioning a nuke. See, there is this huge portion of the map just southwest of Russia, you can't live there anymore. That's what happens when a very small scale and ultimately controlled accident happens at a nuke.

Joseph Willemssen

Seems every real world test that comes out shows the TDI beating the Prius, how do you explain that?

I would explain it by the fact you used the word "seems".

Come to think of it, wasn't this post solely about fuel consumption at high speeds?

This is Green Car Congress. The environmental impact of a technology is always topical.

Chingy

Joe, what's your damage? So this study and the one from CR both showed the TDI beating the Prius in their versions of real world tests. How do you explain that? What do you need to adjust your thinking? I'm completely open-minded, but right now the only information I've seen shows the TDI as the better choice for mileage. Do you have links to any studies which show the Prius as getting better mileage? Let me know.

Mark A

"...as for the accident issue, accidents happen when a driver exceeds the limits of the road surface, their skill, and vehicle maintenance...."

Well Eric, where I live, their is one other factor we are increasingly having to deal with. Deer, feral hogs, or wildlife as a whole. Have you ever hit a deer or a feral hog at 80 mph? Alot of accidents happen around here, at much lower speeds, because of people swerving to miss a wild animal that just jumped in front of them, or wreck plowed into them. Has nothing to do with road surface, driving skill, or vehicle maintenance! Either way, its not good. Body shops, hospitals and funeral parlors are beneficiaries. I agree with fyi CO2, we wont see many people who wreck at 80mph on this site or any site, but at the cemetery site.

To get back on subject, I dont see much use for an test like this. It should be well known here that as the speed increases the mpg decreases due to aerodynamics. Witness the bicycle carrier efficiency numbers at the two speeds. And the Prius owners should quit whining. Their vehicles were designed for much different driving conditions than shown in this test. They should be secure in knowing what their vehicle does and how it performs for them at what it does best.

The only benefit I got from this test was the bicycle carrier difference at 62mph (100kmp). Too bad a graph for this difference was not shown here.

Joseph Willemssen

Do you have links to any studies which show the Prius as getting better mileage?

Greenhybrid.com has 35 users with TDIs averaging 44.0 mpg, with outliers at MIN 30.0 mpg and MAX 53.4 mpg.

They have 638 users with 2nd Gen Priuses averaging 47.6 mpg with outliers at MIN 35.0 and MAX 71.8.

Ash

The Prius is not a good highway MPG car. it's electric moor can help little at highway speeds and it has a large cross section despite it's low drag coefficient.

The Insight is vastly superior in it's aerodynamics to any production car ever made including the prius. It's not just Drag coefficient but also cross section. Too bad they did not include one in this test.

Anyway, the overall point of this study is to show that higher speed = worse MPG.
Enzo Ferrari was wrong, aerodynamics matter!!

George Minko

Well, after tipping off about this test and reading the comments, I get the feeling that only very few commentors really got the point. This test was done to point out how a lead foot can increase your fuel consumption and apart from causing an impact on greenhouse emissions, packs a wallop on your wallet. The test wasn't done to put down the Prius. Apart from that, I think some should realize a few facts: Diesel is not a dirt cheap fuel in Germany at over one euro per litre. In fact there is very little financial advantage compared to Standard/Super. The only advantage is that the diesel here is cleaner, something that needs further development in other countries. In addition, we have something here in europe called a diesel particle filter, on the market already for quite a few years and proven to effectively filter dangerous particles to more or less 100% - even after 100.000 km. The only problem was that it was developed by Peugot. This technology was offered to manufacturers world-wide (of course for a license fee) - all manufacturers declined, wanting to develop their own product, who knows, maybe so they could charge for another extra. Excuse, I diverse. Back to the nitty gritty; you floor it, you pay in cash, you floor it, we all pay the price ecologically. By the way, I don't even drive a diesel, so I wasn't partying for either side. I look forward to the reactions to the next tips I pass on to Mike.

Chingy

Joe, while anecdotal evidence is cool by me, you yourself have poo-poo'd it. I cite the time you took issue with my report that before being broken in, my Golf got 52MPG on regular fossil diesel.

So, what I am looking for is some kind of real-world test like the one above and the other I cited: controlled conditions, replicable results, you know the drill. I tried to find one to no avail.

Patrick

Chingy,

The catastrophe at Chernobyl was related to poor maintenance and poor construction. Since Chernobyl how many nuclear reactors have melted down? How many petroleum based powerplants? You will notice something here...also a chemical plant disruption in India affected 100 times as many people as Chernobyl; should we not build chemical plants?

BTW- Animals and plants are now re establishing themselves around Chernobyl (do a search you'll find a great article from the science journal "Nature"). So much for a nuclear meltdown causing the land to be scorched for thousands of years.

NuShrike

Chingy, I don't think you understand Anne's comment. A diesel has to get 12% BETTER mpg to be EQUAL to a gas car, no matter the efficiency, due to the diesel's higher energy content. I don't think it has been shown that diesel has actually beaten once that percentage is taken into account.

Not only that, I personally have driven a few thousand miles averaging 102km/h, and I get 50mpg when it was averaging 45-47mpg going ~121km/h before. Something is wrong with these "published" Prius numbers.

Otherwise, I wouldn't mind seeing a more efficient diesel/hybrid, or anything else instead of pie-in-the-sky hydrogen.

Joseph Willemssen

Joe, while anecdotal evidence is cool by me, you yourself have poo-poo'd it. I cite the time you took issue with my report that before being broken in, my Golf got 52MPG on regular fossil diesel.

There are certainly potential problem with those datasets, but I wouldn't call a dataset of 638 to be "anecdotal", especially when you're dealing with what should be an objective process (accurately transcribing odometer and fuel pump data). The reason I trust that site the most is that it has the most amount of data over the largest amount of miles. The problems are ones of self-selection, possible lying, and so forth, but as it's an open database, one could see chicanery going both ways. You might wish to contact them to see how well they can vouch for the data.

But that huge dataset is going to be a lot more reliable than a dataset with one point. I don't doubt that you get the mileage you get. What I said is that whatever you get indicates nothing about what people will get overall. For that you need a lot more samples than just one person driving one car.

So, what I am looking for is some kind of real-world test like the one above and the other I cited: controlled conditions, replicable results, you know the drill. I tried to find one to no avail.

A "real world test" does not have controlled conditions and replicable results. That is a specific testing methodology. EPA has theirs, Consumer Reports have theirs, etc. But they're SIMULATING real-world driving. And unsurprisingly, their results vary widely from one another because they're driving the vehicles differently. Car mags are the worst because there's zero science behind what they're doing.

The people who are putting their data in at Greenhybrid own the cars and use them for their transportation. That's real-world data.

I would think you'd be pleased to see the TDI data they have, since it's showing numbers above EPA ratings for the TDIs, whereas the Prius numbers are alomst 8 mpg below EPA.

Leszek Pawlowicz

The problem with this data is that it's obtained using the car's on-board computer, which is notoriously imprecise for measuring this kind of data; driving conditions and technique also play a critical factor. ORNL has published similar data for 1990s cars (available in the DOT's Transportation Data Energy Book), where measurements are done using both real-world driving and dynamometer testing, where fuel consumption is more accurately metered. Their fuel efficiency versus speed curves are dramatically different than the ones posted in this article; they show mileage as being roughly constant from 30 to 60 mph, and only tailing off above that level. I'd take this German data with a huge grain of salt.

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