Prius a gas guzzler compared to BMW 520d

mhaze

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mhaze
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http://driving.timesonline.co.uk/tol/life_and_style/driving/used_car_reviews/article3552994.ece

Looks like a valid comparison between the cars. Prius seriously loses!

A challenge: to drive a Prius to Geneva using motorways and town driving. The direct route is 460 miles but we drove almost 100 miles further to give the Prius the advantage of running in urban conditions where its petrol-electric drivetrain comes into its own. We took along a conventionally powered car – a diesel BMW executive saloon – for comparison and drove both cars an identical number of miles (545).
 
Less spectacular headline:

"BMW makes a diesel car with better fuel economy than their last model, and btw the Prius is not really as economic as advertised, especially at highway speeds."

No, not quite the same ring to that... :p
 
It's worth noting that the article doesn't even mention emissions. Based on numbers from www.greencarsite.co.uk, looks like the Prius produces 10% less C02 per gallon of gas. The article said the BMW got about 5% better fuel economy, so if that C02 number holds then the Prius emitted 5% less C02.

Additionally, I couldn't find smog forming emissions specs on those vehicles in my 2 minute search. Historically, diesels have been very bad for smog emissions, though recently they have cleaned up somewhat.

If you want good fuel economy, purchasing the old Honda Civic HF, at least the local model, would have surpassed those vehicles but been worse than both for emissions. Which vehicle in the test is more eco-friendly is even tested in the challenge they described.

Modern cares make some sacrifice in fuel economy for cleaner emissions. I have no idea which vehicle is better for the environment, but it is best not to equate fuel economy with enviro-friendly.

Walt

Edited to add: the article is specifically titled to mention "gas guzzler" though it does spend time spouting how environmental friendly the Prius is.
 
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I bought a 1989 Honda Accord recently. I don't know about emissions, but according to my calculations, I'm getting close to 38 miles to the gallon.

I don't feel so bad anymore that I can't afford a hybrid.
 
Here's another thing to keep in mind: suppose you commute 10,000 mi per year. In a 12 mpg heavy pickup, that's 820 gallons. In a 15 mpg SUV, it's 666 gallons. In a 20 mpg minivan, it's 500. In a 35 mpg Civic, it's 280 gallons. In a 45 mpg hybrid, it's 222 gallons.

Notice that you can save 150 gallons by switching from a pickup to an SUV, or save 58 gallons switching from a Civic to a Prius. A small change in a gas-guzzler is worth more than a revolutionary upgrade to a gas-miser. It's really gallons per mile you should look at, not miles per gallon.

If you want to spend $40,000 on transportation and want to actually minimize your carbon footprint, don't buy a Prius. Buy three Toyota Yaris at $13,000 and 35mpg each. Give one to your Suburban-driving mother, one to your 1974 Dodge-driving brother-in-law, and keep one for yourself. (Take the old cars directly to the scrapyard; do not sell them used.) Voila! You've just saved 3 x 400 gallons per 10K miles. And you gave your mother a car, what a good kid!
 
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Walter Wayne said:
Carbon monoxide, off the top of my head. Not sure if there are other destinations as well.
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Scary* it is. And silly. No wonder the fuel economy is disappointing**. :rolleyes:

Anyway, my car gets 143 miles*** to the gallon****.:rolleyes::rolleyes:

*) CO is just about as scary as gases get.

**) A high level of CO emission is a sign of incomplete (read: inefficient) combustion.

***) Whenever i go for a run, I use the ridiculously short North-Welsh mile to measure distance.

****) And then I must admit I usually have a beer. And I always insist on using generous traditional Argentinian volume units.
 
Walter Wayne said:
It's worth noting that the article doesn't even mention emissions. Based on numbers from www.greencarsite.co.uk, looks like the Prius produces 10% less C02 per gallon of gas. The article said the BMW got about 5% better fuel economy, so if that C02 number holds then the Prius emitted 5% less C02.

Additionally, I couldn't find smog forming emissions specs on those vehicles in my 2 minute search. Historically, diesels have been very bad for smog emissions, though recently they have cleaned up somewhat.

If you want good fuel economy, purchasing the old Honda Civic HF, at least the local model, would have surpassed those vehicles but been worse than both for emissions. Which vehicle in the test is more eco-friendly is even tested in the challenge they described.

Modern cares make some sacrifice in fuel economy for cleaner emissions. I have no idea which vehicle is better for the environment, but it is best not to equate fuel economy with enviro-friendly.

Walt

Edited to add: the article is specifically titled to mention "gas guzzler" though it does spend time spouting how environmental friendly the Prius is.
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Someone please correct me if I'm wrong but from my understanding, the more efficiently you burn a gallon of gas the more CO2 and the less efficient the burn, you get a higher proportion of CO compared with CO2. If I'm correct in this, the more CO2 emissions per gallon, the more efficient the engine is running and better utilizes the energy contained in the gallon of petrol. If it was super inefficient, you would have left over unused hydro carbon molecules, not exactly a good thing.
I believe this is also how you measure the efficiency of natural gas and oil home heaters: by measuring the portioning of CO2 to CO. The more CO2 emissions per unit of fuel, the more efficient and therefore, more environmentally friendly.
 
Walter Wayne said:
It's worth noting that the article doesn't even mention emissions. Based on numbers from www.greencarsite.co.uk, looks like the Prius produces 10% less C02 per gallon of gas. The article said the BMW got about 5% better fuel economy, so if that C02 number holds then the Prius emitted 5% less C02..
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That's 10% less CO2 than a diesel. Assumably true for every gas vs diesel comparison.

Now compare mileage within the same class of car, gas vs diesel. Or a diesel hybrid vs gas hybrid of the same model.
 
Yeah, I realised that there was something in my post which contradict basic combustion theory and had to go on a little search to find out why the deviation from ideal. I found the answer and it was lean burn.

Burning lean reduces some engine inefficiencies when backed off from full throttle and allows higher compression ratios. The cost is an increase emissions.

Walt
 
Walter Wayne said:
It's worth noting that the article doesn't even mention emissions. Based on numbers from www.greencarsite.co.uk, looks like the Prius produces 10% less C02 per gallon of gas. The article said the BMW got about 5% better fuel economy, so if that C02 number holds then the Prius emitted 5% less C02.
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The 10% difference is related to fuel density (diesel and petrol/gas are about the same %carbon by mass, but have different densities kg/litre), and I suspect there is some journalistic licence involved here (if emissions suited the story, it probably would have been reported). That said - the focus of the story is related to the accuracy of manufacturers claims and the reality of use - 48 mpg vs. manufacturers 65 for the prius, "over 50" (ish?) mpg vs. 55 mpg claim for the BMW, which is a story in itself.

It is difficult to gauge the exact difference because of the vagueness in the report - "over 50mpg" vs. "48.1mpg", they give the amount used by the BMW (49 litres, probably subject to vagueries of pump cut offs) but do not give the exact mileage (560 miles at the top, a bit less further down). So we can't really nail down exactly which had the lowest emissions - unless I missed something again - beyond saying they were pretty close. Perhaps journalistic licence applies here and if the emissions figure suited the article, it would have been reported.

Whether the test journey was fair and representative is a valid question, but they make the point that other journalists have made similar observations about the ability of the prius.

Walter Wayne said:
If you want good fuel economy, purchasing the old Honda Civic HF, at least the local model, would have surpassed those vehicles but been worse than both for emissions. Which vehicle in the test is more eco-friendly is even tested in the challenge they described.
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Slightly missing the point of the article I think - they could have beaten both comfortably with the new Mini D or similar vehicles (good grief starting to sound like a BM commercial here) - the point was more to do with public perception between (say) a prius and a debadged executive saloon. Most would assume the former is saving the planet whereas the later is an carbon hog - hence the perks afforded to the prius (congestion charge in London, car pool lanes in the US). However, the differences between these two are actually rather less than perceived, both by the public, and apparently by legislators in both countries.

This is really a case of unintended consequences. A lot of people demand action on CO2 emissions, but most of the demands are actually rather less effective than people realise - whether it be cars that aren't actually as good as claimed, wind farms that produce rather less power than their original design said they would, or biofuels which don't really save much in the way of CO2 but can have land use change consequence and possible food price consequence.

Sometimes the populist, fashionable, knee-jerk reactions to perceived problems turn out to be not to be so good in the cold light of simple, rational analysis.
 
casebro said:
That's 10% less CO2 than a diesel. Assumably true for every gas vs diesel comparison.

Now compare mileage within the same class of car, gas vs diesel. Or a diesel hybrid vs gas hybrid of the same model.
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It does not seem likely that there is that high a density difference, and assuming both are pure hydrocarbons it is pretty safe to think of most of the mass as being the carbon. Certainly not a 10% difference from the number of hydrogens on a carbon chain.
 
CoolSceptic said:
Sometimes the populist, fashionable, knee-jerk reactions to perceived problems turn out to be not to be so good in the cold light of simple, rational analysis.
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And I am still not sure based on the info I can find what is the best choice. I did a quick look at the London Congestion Charge thinking they may be doing something smart, like charging vehicles based on emissions harmful at the local level. No such luck, the London Congestion Charge seems to focus on CO2 emissions from what I've seen, in which case the choice of vehicles to give exemption too seems to not fall in line with the stated mission.

I haven't been able to find a comparision of various tail-pipe emissions for these cars, with the exception of C02. The EPA green vehicle guide does give levels of other emissions and gives an overall "Air Pollution Score", but it focuses on american vehicles, and as such few diesels are available for comparison. I know when I test drove the Insight back in 2000/2001 time frame, compared to the Volkswagon diesel, it was slightly better on C02 rating, but far better when other emissions were taken into account.

So simple rational analysis remains difficult for me, as I simply don't have all the facts. Focuses on gas mileage and C02 emissions are still just part of the story.

Walt
 
Of course, there may be no reason to be concerned to any large extent about emissions. We have various regulations, we pay various fees, we have various pollution reducing equipment on vehicles. Over and above these factors, can one ascribe some level of "social good" to higher vs. lower emissions of various sorts? I am skeptical about such a thing. Basically it implies that someone's personal opinion about emissions is superior to that of the state or federal regulatory agency which has set the standards that apply in the area in question and for which compliance to that level - not beyond - is required.

Now, notice the trend of this thread.

1. Statement is made that a pretty nice BMW beat the Prius on gas mileage.
2. People start bringing up relative emissions.

Question: Why? As if, "Oh the Prius is still GOOD?"

Well, no, it is considerably less good. What has happened is that the myth of it's great mileage just flew out the window. Other problems with Prius -

Prius Shuts Down in the Snow (Consumer Affairs)
Prius Stalls in Snow (Consumer Affairs)
Savings at Pump Don't Offset Higher Purchase Price (Consumer Affairs)
The costly secrets of hybrid cars (MSN Money)
 
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robinson said:
Unless you look at the bottom line. The BMW cost three times as much.
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I'll certainly accept that as a criticism against the BMW, although that can operate in reverse, too: Someone who may have wanted a luxury car (eg who wanted to spend 3x), but who was leaning toward the Prius for do gooder for the environment reasons, might well on reading this review go ahead and get the luxury car.

By the way I've driven Prius and liked the acceleration and ride, just don't think it's the only nice thing in the store.
 
ponderingturtle said:
It does not seem likely that there is that high a density difference, and assuming both are pure hydrocarbons it is pretty safe to think of most of the mass as being the carbon. Certainly not a 10% difference from the number of hydrogens on a carbon chain.
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It does according to wikipedia, so the fair way to compare the emissions would be in kg of CO2 per kilometer.
 
H'ethetheth said:
It does according to wikipedia, so the fair way to compare the emissions would be in kg of CO2 per kilometer.
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Yes I checked it out and found that gas weighs between 90% and 75% of the wieght pre gallon of deisel. Depending on the type of deisel.

So my thoughts that they would have roughly the same density where wrong.
 
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