BMW beats Prius in MPG test

[itsrobert]

http://www.autoblog.com/2008/03/23/bmw-520d-beats-prius-in-gas-mileage/

[GodlessBiker]

1. Bogus. They should do equal amounts of highway and city driving.

[itsrobert]

2. Why? I do a lot more highway driving.

Do most people take the back city roads to see Grandma?

[GodlessBiker]

16. If Grandma lives on East 83rd Street, yeah.

[itsrobert]

22. than maybe taking public transportation is the answer

take the subway.

[OKIsItJustMe]

4. You know... it doesn't matter that much

The fact that you have a significantly heavier, conventional auto, getting comparable mileage to the much more mechanically complicated Prius highlights just how unremarkable its mileage is.

The question I've always asked is, "Is the mileage enough better to justify all of the added complexity?"

[lectrobyte]

7. mechanically complicated? Much less moving parts in a Prius than

conventional cars.

[OKIsItJustMe]

9. You're joking. (Right?)

A Prius has an internal combustion engine, like a "normal car."
Plus:
An electric motor.
A funky transmission to tie them both together.
Regenerative braking.

http://www.asashop.org/autoinc/april2002/collision.htm


http://auto.howstuffworks.com/hybrid-car6.htm

[lectrobyte]

24. Not joking at all.

The electric motor/generator replaces both the alternator and starter in a conventional car. The Prius uses the electric motor for reverse, so the transmission is even more simplified, even after considering that a CVT has less moving parts than an equivalent automatic.

[OKIsItJustMe]

29. I just don't see how this is simpler

The majority of moving parts in a conventional car are in the internal combustion engine, which gets carried over intact to the Prius.

The alternator & starter in a conventional car really are not very complicated. So, replacing them with a single large unit doesn't impress me much as far as simplification.

The CVT is a fine thing, but can be installed in a standard car just as well.

Now all you have to do is find the equivalents in a standard car for the regenerative braking and the large battery pack.


Don't mistake me. For years I've described the Prius as a very good implementation of a questionable technology. I think Toyota's done a fine job of building it. I just don't think a parallel hybrid is a good solution.

[Howzit]

31. You are missing the point. Actual user MPG is not important.

The Pruis symbolizes environmentalism, while any BMW symbolizes capitalism. That is, unless the BMW runs on hydrogen. But then, we all know that water vapor is a more potent greenhouse gas than CO2, so BMW is just pretending to care.

[GodlessBiker]

15. I'm getting 44 mpg with my Prius. I'll take the complexity.

[OKIsItJustMe]

23. Not everyone has had such good luck

http://www.consumeraffairs.com/automotive/toyota_prius.html

[lectrobyte]

25. Do not confuse consumer affairs with consumer reports or any

other legit site. They have a definite agenda, read some of their articles and decide for yourself.

[OKIsItJustMe]

28. If you say so

Here's (what I believe is) a legitimate site, with questions and answers:
http://townhall-talk.edmunds.com/WebX/.f0ff5f5/

[lectrobyte]

30. I'd trust edmunds way more than consumeraffairs.com

Thanks for the link, I didn't realize Edmunds had a discussion board.

[tvoss]

27. I'm getting 40mpg in my 96 Saturn S series

Best value out there for high gas milage. I bought it when gas went to $1.90 a gallon and it has already paid for itself in savings over my truck.

[Howzit]

32. Real MPG doesn't count.

Your car doesn't show that you want to preserve the earth the way a Prius does. Your car says you like to preserve personal funds. That could make you a capitalist.

[OKIsItJustMe]

33. As I've mentioned before, in the 80's, I drove a Nissan/Datsun 210

I loved that car. It reliably gave me 35+ MPG (40+ on road trips.) This is why I've been so unimpressed with the mileage offered by the Prius.

[tinrobot]

3. Different fuels, so it's hard to truly compare.

A gallon of diesel is not the same as a gallon of gasoline.

[OKIsItJustMe]

5. It's not diesel fuel that makes a diesel vehicle more efficient

http://en.wikipedia.org/wiki/Fuel_efficiency
http://auto.howstuffworks.com/diesel.htm

[wtmusic]

6. Thanks for providing links to debunk your own nonsense.

Diesel 38.60 megajoules/liter
Regular gasoline 34.83 megajoules/liter

http://en.wikipedia.org/wiki/Fuel_efficiency

(Sorry if I wasn't supposed to read them)

[OKIsItJustMe]

11. I guess you didn't read very much of them

Yes, diesel fuel has a little more energy per gallon, but that's not the source of a diesel engine's efficiency.
http://en.wikipedia.org/wiki/Diesel_engine#Advantages_and_disadvantages_versus_spark-ignition_engines

...

Diesel engines are more efficient than gasoline (petrol) engines of the same power, resulting in lower fuel consumption. A common margin is 40% more miles per gallon for an efficient turbodiesel. For example, the current model Škoda Octavia, using Volkswagen Group engines, has a combined Euro rating of 38 miles per US gallon (6.2 L/100 km) for the 102 bhp (76 kW) petrol engine and 54 mpg (4.4 L/100 km) for the 105 bhp (78 kW) diesel engine. However, such a comparison doesn't take into account that diesel fuel is denser and contains about 15% more energy by volume. Although the calorific value of the fuel is slightly lower at 45.3 MJ/kg (megajoules per kilogram) than gasoline at 45.8 MJ/kg, liquid diesel fuel is significantly denser than liquid gasoline. When this is taken into account, diesel fuel has a higher energy density than petrol; this volumetric measure is the main concern of many people, as diesel fuel is sold by volume, not weight, and must be transported and stored in tanks of fixed size.

Adjusting the numbers to account for the energy density of diesel fuel, one finds the overall energy efficiency of the aforementioned paragraph is still about 20% greater for the diesel version, despite the weight penalty of the diesel engine. When comparing engines of relatively low power for the vehicle's weight (such as the 75 hp VW Golf), the diesel's overall energy efficiency advantage is reduced further but still between 10 and 15 percent.

...

http://en.wikipedia.org/wiki/Diesel_cycle

...

Comparing the two formulae it can be seen that for a given compression ratio (r), the ideal Otto cycle will be more efficient. However, a diesel engine will be more efficient overall since it will have the ability to operate at higher compression ratios. If a petrol engine was to have the same compression ratio, then knocking (self-ignition) would occur and this would severely reduce the efficiency, whereas in a diesel engine, the self ignition is the desired behavior. Additionally, both of these cycles are only idealizations, and the actual behavior does not divide as clearly or sharply. And the ideal Otto cycle formula stated above does not include throttling losses, which do not apply to diesel engines.

...

[wtmusic]

12. As tinrobot so aptly said,

"Different fuels, so it's hard to compare."

They are using two fuels with different amounts of energy per gallon and then evaluating two cars by the miles they get -- per gallon.

Are you defending this asinine experiment, or just backed into a corner and can't admit you're wrong?

[OKIsItJustMe]

19. No, it really isn't hard to compare.

One is straight-forward technology.

The other is (while not exactly a "Rube Goldberg") more complex, more difficult to maintain, and more prone to failure.

I believe the point is valid.

[tinrobot]

34. Let's do the math.

Diesel 38.60 megajoules/liter
Regular gasoline 34.83 megajoules/liter

38.60 / 34.83 = 1.108

Looks like diesel has about 10.8 % more energy than gasoline.

So, let's factor that into the freeway driving test performed in the article:

BMW 520d - 50.3 mpg
Toyota Prius - 48.1 mpg

48.1mpg * 1.108 = 53.3 mpg corrected.

So, by simply correcting for the energy density of the fuel, the Prius wins by a little. But it's pretty cool that the BMW gets so close. I'm really interested in seeing how diesel hybrids perform in real world tests.

[Howzit]

36. If your measure of winning is MPG, then

the Prius won, a little. If you measure work done and fuel consumed while doing that work, then the Prius doesn't win: Five series BMW is heavier than a Prius with more frontal area and worse drage co-efficient, as in doing more work.

It's a silly contest, but if the BMW had been running on bio-diesel everyone would be singing Cumba Ya.

The simple facts are that regenerative braking has its advantage in city driving and is well suited to public buses that make frequent stops. Also, there are plenty of non-hybrids achieving averages of 35 to 40 MPG everyday without any fanfare or green points.

[TreasonousBastard]

8. And the BMW ran it's A/C during the test...

losing a couple more MPG.

It was a silly test, more for PR than any scientific results, but it does point out that hybrids are still only a stopgap until some newer technology comes around.

My Saturn LS1, almost exactly the same size as a Mercedes E, gave me about 30 overall, with slightly over 35 highway. Camrys and Accords with similar 4 cylinder engines are known to give similar mileage.

So...

30 MPG means you're using 33.3 gallons of fuel every 1,000 miles.
50 MPG means you're using 20 gallons for the same distance.

You saved a rousing 13 gallons for every 1,000 miles you drive carrying around all those batteries. Even less if you passed on the 35MPG Yaris (that costs 10-12 grand less) while at the Toyota dealer.

So, if I had my choice of all the cars available right here and now, I'd get a cheap used van for hauling stuff, and a Yaris, Mini, or Mercedes Bluetech (depending on how much scratch I had at the time-- all three if I won the Lottery) as the main ride.

[lectrobyte]

10. Good for you. The Yaris won't haul a clothes dryer like my Prius can,

who needs a big truck with 4x4 on the side?

[CRF450]

13. I do

Sure a prius or any hatchback/station wagon can cary all the pool/spa cleaning supplies I need for the job, but I dont want to be in an inclosed vehicles with buckets that reak of chlorine. Plus the clorine fumes can rust and damage most any metal parts.

[wtmusic]

14. Great photo

but looks like you kinda had to dismantle the rear seat to pull it off...

[One_Life_To_Give]

17. Apples and Oranges comparison

Hybrid drives are optimizations for stop and go driving, such as is common in urban areas. Note unlike an ordinary vehical the Prius actually gets better mileage in the city than on the highway. For constant speed driving such as long hauls on the interstate highways the thermal efficiency of the Diesel will outperform an equivalent gasoline engine. Which is why you will find a number of old diesel cars such as the VW Rabbit which can get better highway mileage than a Prius. Although in the US I beleive the Insight is still the highest for production model highway mileage.

FYI - Last I checked the record for the most thermally efficient engine (Ratio of Chemical energy intake to mechanical energy output) is the Wartsila Diesel which is being used in container ships.

[itsrobert]

18. Urban areas don't have highways?

I routinely drive on the freeways of Orange, LA, and San Diego Counties. Most of my driving is at speeds of 55mph or greater on highways. Like most people.

[One_Life_To_Give]

21. Didn't intend to imply any such thing

Only intended to imply that Urban area's more typically have congestion and frequent cross streets. As opposed to some rural areas where the next cross street may be tens of miles away.

In the end the car is designed/ optimized for a certain profile of driving. If that happens to be close to what you actually drive then it can be a good choice.

[depakid]

26. "Like most people."

LOL.

Southern Californians aren't "like most people."

And if you live there- you're NOT spending most of your time going 55.

[itsrobert]

35. Really, you're right. I'm spending most of my time going 65+

Thank you.

[Nihil]

20. More wankery from the car supplement press

> the Prius the advantage of running in urban conditions
> (vs)
> a diesel BMW executive saloon

Apples & oranges comparison on the test design.


> the entry level car of the 5-series ... the cheapest option at £27,190.

Whereas the Prius was the top of the range T Spirit at £20,677.
(The entry level Prius is the T3 at a list price of £17,782)

Apples & oranges comparison on the models chosen.


> Admittedly, we find the test a bit unfair -- the Prius is not meant show
> its muscle at "75-mph into a headwind," and adding 100 miles of urban
> driving doesn't make up for 460 miles of autoroute.

Apples & oranges comparison on the test environment.


> (petrol) Prius against a (diesel) BMW

Apples & oranges comparison on the fuel consumption (petrol <> diesel).


> ... and avoided turning on the stereo in an effort to conserve power.

Has no-one told him that the Prius uses a standard battery for the usual
auto stuff (e.g., stereo) and a special battery pack for the engine stuff?
Not that he just wanted to suggest that "green is hard" of course ...


And the BMW wasn't even a genuine "executive saloon" at that:
> six-speed manual transmission needs quite a lot of work but if you are
> concerned about fuel economy then it’s a small price to pay for the extra
> 5mpg that it gains over the automatic version.

... which is more than double the claimed "win" by the "executive saloon"!


> And the diesel's CO2 emissions are just 32 g/km higher than the hybrid

So over the 545 mile run, the BMW spat out an extra 27.9 kilograms of CO2
and only "beat" the Prius by using a manual transmission and a rigged test
course.

Ho hum :eyes:

This "win" would cost him an extra £6,500 to £10,000 difference in list
price, an extra £100 per year in road tax.

This outlay would "save" him a grand total of £0.45 *only* under conditions
that match the (rigged) test ... conditions that he simply will not find
in the UK ... and, while doing so, will generate an extra 51g of CO2 for
every mile he drives.

Lets just repeat that last point: the BMW produces 31% more CO2 per mile.

He should give up pretending to be a journalist and become a greengrocer
for the amount of apples & oranges he displayed.