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May
19

The Prius Deception . . . The Other Side of the Argument

I recently received a thoughtful comment on my original Prius Deception post by David H. Hawkins.  In his comment, Mr. Hawkins basically says that I’m full of crap with many (most, actually) of the claims I make – if he knew me, he might not limit his findings to the post in question.  In his comments, he claims that “this article contains a plethora of incorrect ‘facts’ and suppositions” and outlines what  he believes are my “fallacious facts.”  Since I thought his text was insightful, and he seems like a reasonable, intelligent man, I thought I would put my comments on it in a new post rather than in an extended comment to the original.

Below are Mr. Hawkins’ explanations of my allegedly fallacious statements, the truth as he sees it and my further thoughts on the particular topic.

Fallacy:  The difference in price for a Prius over another comparably equipped mid-size car will buy all the gas you would need for the life of the car.

Truth:  If I WERE paying $3000.00 more than a comparably equipped mid-size car (which I am not).  At todays prices, the car would pay for the difference in between 2 and 4 years depending on how much I drive, and I expect gas to go up even more in price.

Will: Well this one is actually pretty simple to validate.  We’ll pick a “comparable” vehicle in the mid-size segment.  How ‘bout the Toyota Camry CE (4–cylinder car).  The Camry is a great car, it’s actually larger in interior space and exterior dimensions, is more luxurious and is faster than the Prius – although arguably not significantly different from the Prius in any of these aspects.  Of course, it’s also manufactured by the same company, Toyota, which hopefully removes some other variables in differentiation.  According to Edmunds, the average selling price (the price people are actually paying for the car) of the new Camry is $19,300.  According to the same source, the average price people are paying for a new Prius is $24,900 (this assumes equivalent options – the Prius must include the optional HF package which adds front seat-mounted side and front and rear side curtain airbags and 6–speaker stereo to be equipped almost identically to the base Camry).  Thus, the difference in purchase price is $5,600.

The Prius gets much better gas mileage than the Camry.  The actual mileage numbers gleaned from various car magazines and car review web sites are the mid-to-high 40s mpg for the Prius and about 30 mpg for the Camry – obviously, these are city/highway combined numbers.  For the sake of discussion, let’s give the Prius the benefit of the doubt and use 50 mpg for the Prius and 30 for the Camry.  Assuming that the average driver drives 12,000 miles/year and gas costs $3.50/gallon, the Prius driver will spend $840 for gasoline/year ((12,000 mi/50 mpg) * $3.50).  Using the same calculation, the Camry driver will spend $1,400 for gasoline in one year.  The difference being $560 per year.

Since the difference in purchase price, as outlined above, is $5,600, it’s clear that it would take 10 years to break even financially on the decision to buy the Prius.  Of course, this does not even include the facts that 1) batteries lose efficiency over time, 2) 10 years is already outside the envelope that Toyota prescribes as the useful life of the battery, 3) internal combustion engines are more efficient after break-in and, 4) the opportunity costs on $5,600 can be significant for many.

Fallacy:    Battery technology evolves at a glacial pace.  There may be breakthroughs in the future in alternative technologies (e.g. fuel cells), but the standard chemical reaction in batteries has not improved much in a very long time.  Quantum improvements in engine mechanicals and fuel chemistry will happen long before similar improvements in battery technology.

Truth:  By this argument, anything on wheels is obsolete, wheels haven’t changed in centuries.  Batteries HAVE come a LONG way, from lead/acid to carbon/zinc to lithium ion.  I should point out that the battery in a current model Prius puts out over 200 volts and is raised to 500 volts for use in the engines.  (as a side note, street cars run on about 600 volts, and no one complains about their efficiency.)  Also, the battery is only used in situations where the gas engine is very inefficient, such as low speeds and high acceleration.

Will: Sorry, David, I don’t understand what the wheel comparison means.  If you believe that I am stating that batteries are obsolete, you need to read my entire post in which I state that I’d love to see simple diesel/electric hybrids with electric motors used to keep diesel engines in their peak torque range.  That aside, the combination of batteries and electric motors HAVE actually increased in efficiency at a glacial pace compared to the combination of internal combustion engines and fossil fuels (this does not mean, BTW, that batteries have not evolved and that new battery technology, as you state, has not been introduced).  And this is true even considering the fact that fossil fuel efficiency is virtually unchanged (actually, it has probably decreased since all the old additives have been removed).  Engine technology has grown by leaps and bounds over the last two decades.  Much by electronics, but quite a bit mechanically as well.  The average horsepower/liter of engine displacement is up tremendously.  The output of battery powered electric motors has increased as well, but not nearly as much as for engine/fuel combination.  Even more to the point, the prospects for further electrical and mechanical advances in internal combustion engines looks like it will outstrip advances in battery technology for the foreseeable future.

Fallacy:  Batteries weigh a lot!  My friend John Bower likes to quote a Ford engineer who said: “electric cars are a brilliant solution for the task of hauling around 1,500 lbs worth of batteries.”  All that weight has to be propelled by something and that something is gonna need fuel to run it – whether it be electricity or fossil fuel.  Electric motors are very linear.  If you want more power, you need more batteries.

Truth:  The battery in a Prius only weighs about 100 pounds!
How much do you think a tank with 20 gallons of gas weighs?
(Just for the record, it weighs 124.32 pounds!)

Will: David is right on this one.  The battery on the Prius weighs about 100 pounds.  A truly amazing feat considering all that it does in the Prius.

This one is true:    The Prius has an EPA rating of 60 mpg in the city and 51 mpg on the highway (city numbers are higher because the drivetrain relies on batteries for power in stop-and-go traffic).  The EPA does not get these numbers by driving around, though.  They take the engine out of the car and put it on a dynamometer to measure it in a lab.  During these tests, the maximum acceleration used is 3.3mph per second – which is how fast you’ll drive on your 97th birthday.  Also, the tests are done with the air conditioning off.  With the extra load on the engine, some tests have shown the Prius’ fuel economy drops by as much as 33%.  In Europe, the car is rated at 47mpg in the city and 56mpg on the highway.  The European ratings are done with the engine mounted in a car, under the hood although, apparently, they still drive pretty slowly.

BUT…:  These figures are quoted by Toyota because they MUST BE BY LAW.  Anyone with sense knows “your milage will vary”!  Most Prius purchasers know enough to expect around 45 to 50 MPG.  Still a lot better than most of the other cars on the road.  Also, the Prius has 295 Ft/Lbs or torque. and that is usable from a standing
start.  The Nissan Z sports car only has about 270 Ft/Lbs torque and that is at an engine speed of 4800 RPM, certainly not from a standing start which is where I personally WANT to have most of my torque overcoming the static friction and inertia of a dead stop.  I also question the quoted  European milage figures because hybrid cars like the Prius get BETTER milage in the city than on the open highway.  The above figures (if correct) are at least reversed.

Will: Actually, David, most car buyers don’t really get the fact that “their actual mileage may vary.”  Even when they do, they believe that there is a slight difference between the EPA numbers and actual mileage.  The Prius’ numbers, however, are significantly different.  You are correct, though, that Toyota MUST publish the EPA numbers.  The law does not say, however, that they can’t publish their own real numbers as well.

You are also correct that the Prius has ~295 ft/lbs of torque available.  This torque is almost all from the electric motors – the gasoline engine puts out an incredibly anaemic 82 ft/lbs of torque.  Electric motors are great at applying even torque across a broad band of motor rpm.  The problem in the Prius’ implementation is that the batteries can’t support the application of that high level of torque for very long.  Great for getting off the line, but not much help 10 seconds after the light turns green.  It should be noted that Toyota claims that the maximum torque for the car takes place at 4200 rpm (I assume that’s engine rpm, not electric motor rpm).  Of course all this is why the Prius accelerates from 0–60 mph in 10.37 seconds.   For reference, the Camry accomplishes this same feat in 8.6 seconds.

Finally, while you’re correct that you want the torque off the line, it’s the results that matter.  Using your comparison, the Nissan 350Z with it’s maximum torque of 270 ft/lbs held at bay until the engine hits 4800 rpm reaches 30 mph in less than 2.5 seconds.  The Prius, with its 295 ft/lbs of torque available as soon as the light turns green takes 3.4 seconds to get to 30.  Of course, if you make this comparison on the continual application of torque, the Z takes about half the time that the Prius does to get to 60 mph.  I don’t believe that these two cars should be compared.  I’m just using your examples to show that the engine specs aren’t indicative of the actual performance.

Also, as a side note, I am an engineer.  To anyone who appreciates engineering works of art, the Prius is the Mona Lisa.  Its internal design is a masterpiece of engineering elegance.

Will: I too am an engineer.  To be sure, the Prius is an engineering marvel and Toyota is a great engineering company.  As I said in my original post, I’m not out to bash the Prius or its manufacturer, Toyota.  The Prius is a good car with terrific technology.  My point is that it’s not what the American public believes it is.  There are better solutions to the problem; many of them available now and many of them considerably cheaper than the gasoline/electric hybrid.  Even more solutions would be available immediately or in short order with minor policy changes in this country (e.g. 5 states don’t even allow the sale of new diesel-powered cars, one of them California – what incentive does this give the European manufacturers of diesel cars to ship to the US?).

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 May 19th, 2006  
 Will  
 Stuff with a Motor  
   
 4 Comments

4 Responses to The Prius Deception . . . The Other Side of the Argument

  1. A couple of thoughts on the Prius. First I r an engineer too and don’t forget it.  So I must be right.. I think a more appropriate term is Prius Self Deception I am not sure about the one fellow’s statement of about having torque to overcome static friction. Static friction where? fluid lubricated journal bearings, antifriction roller bearings, static friction is of nominal consequence in these types of interfaces. One place where I definitely WANT NOT to overcome static friction is between my tires and the road. Otherwise you have a dragster style smoky burnout which is real bad for your gas mileage, tire life and keeping points off your driver’s license. One thing that I think people have completely lost track of is what the Prius is really about. Go to the Toyota Website, the purpose of the Hybrid system is not merely to get high gas mileage, it is also to reduce emissions, which it does very very well at. The Prius puts out about 1/10 what the average Low Emissions Vehicle does. Most people can’t get excited about this fact because it doesn’t translate into any personal gain. If carbon credits could be bought or sold on ebay, it might be a different story. About disappointing gas mileage. All I can say is people are stupid. At 50 MPG a 10% reduction in mileage seems like a huge drop of 5 MPG, on the other hand at 18 MPG a 10% mileage increase doesn’t seem all that spectacular, “um yea, I get about 18-20 MPG on the freeway”.  Even when we do think about, most people look at the raw number, not adjust it proportionally. Now I spent a little time poking around the Prius/Hybrid website blog thingys and there is a lot misconception. Years ago, BMW did a study on methods of improving gas mileage. Accelerating briskly, but in as high a gear as possible (ie lug the engine), produced better mileage in stop and go traffic, than slow acceleration in lower gears. Why? Pumping losses, gas engines are slowed down by restricting airflow past the throttle plates. Holding the throttle near wide open reduces pumping losses. That being said, I can’t see this as being too substantial effect from 0-40 MPH. Certainly accelerating like a slug though doesn’t buy you anything, other than a chance to sit at the next red light. Some Prius owners are put off by the engine revving in some situations during slow acceleration (the engine kicks in to recharge the battery) and they think this is screwing up the gas mileage. Um let me see, the Prius drivetrain engineers must not know a thing about the specific efficiency of the combined engine / generator / battery combination. Idiots. It almost certainly revs to the most desirable speed taking into account may factors. The air conditioner mileage hit. Freakin’ Morons, just shut up. Air conditioners need energy to run, why do you think they ask you to turn off your AC at home when there is a threat of brown out /blackouts. Perhaps all cars should have a display that shows you how many gallons of gas per hour is being used by each accessory, as opposed to showing your change in mileage.         Accessory              (gas consumption .01 gallons/hr)               AC                                        250                                 4 DVD players                           95  left turn signal that has been left on for the past 75 miles                                  10 You pay as much for the privilege of air conditioning in a Prius as you would in another equivalently sized car with the same paint  and interior colors. Hint: get rid or your black car with the black interior. Economic justification: Right now, personally, it is probably hard to justify a Prius over an equivalently equipped econobox. Perhaps if one’s driving conditions optimally match the Prius, and if gas is expensive enough. I don’t think we know quite what the Lifetime TCO is on these things. Battery life is frequently brought up in these discussions, but CA requires they be warranted for 150,000 miles, that ain’t bad.  If you are a single commuter and you get to save time on your commute since you will be able to now drive in the HOV lane, it seems a no brainer if it only knocks 5-10 minutes off of your commute. To look at this from a different perspective. A lot of people pay a premium to have a high performance vehicle, higher acceleration, better cornering, higher top speed. Do you think that this extra performance reduces ones in transit time by even 2% over the lifetime of the vehicle. Probably not (with perhaps a few exceptions). You normally don’t see people complaining, “dammit, ya know, when I had that Nissan Sentra I couldn’t get over 85 MPH and my commute from Silicon Valley took 75 minutes, now with this Vette, it’s got a top speed over double that, and I only cut 2 minutes of my commute. WTF GM really misled me on this one.”

  2. A couple of thoughts on the Prius. First I r an engineer too and don’t forget it.  So I must be right..

    I think a more appropriate term is Prius Self Deception

    I am not sure about the one fellow’s statement of about having torque to overcome static friction. Static friction where? fluid lubricated journal bearings, antifriction roller bearings, static friction is of nominal consequence in these types of interfaces. One place where I definitely WANT NOT to overcome static friction is between my tires and the road. Otherwise you have a dragster style smoky burnout which is real bad for your gas mileage, tire life and keeping points off your driver’s license.

    One thing that I think people have completely lost track of is what the Prius is really about. Go to the Toyota Website, the purpose of the Hybrid system is not merely to get high gas mileage, it is also to reduce emissions, which it does very very well at. The Prius puts out about 1/10 what the average Low Emissions Vehicle does. Most people can’t get excited about this fact because it doesn’t translate into any personal gain. If carbon credits could be bought or sold on ebay, it might be a different story.

    About disappointing gas mileage. All I can say is people are stupid. At 50 MPG a 10% reduction in mileage seems like a huge drop of 5 MPG, on the other hand at 18 MPG a 10% mileage increase doesn’t seem all that spectacular, “um yea, I get about 18-20 MPG on the freeway”.  Even when we do think about, most people look at the raw number, not adjust it proportionally.

    Now I spent a little time poking around the Prius/Hybrid website blog thingys and there is a lot misconception. Years ago, BMW did a study on methods of improving gas mileage. Accelerating briskly, but in as high a gear as possible (ie lug the engine), produced better mileage in stop and go traffic, than slow acceleration in lower gears. Why? Pumping losses, gas engines are slowed down by restricting airflow past the throttle plates. Holding the throttle near wide open reduces pumping losses. That being said, I can’t see this as being too substantial effect from 0-40 MPH. Certainly accelerating like a slug though doesn’t buy you anything, other than a chance to sit at the next red light.

    Some Prius owners are put off by the engine revving in some situations during slow acceleration (the engine kicks in to recharge the battery) and they think this is screwing up the gas mileage. Um let me see, the Prius drivetrain engineers must not know a thing about the specific efficiency of the combined engine / generator / battery combination. Idiots. It almost certainly revs to the most desirable speed taking into account may factors.

    The air conditioner mileage hit. Freakin’ Morons, just shut up. Air conditioners need energy to run, why do you think they ask you to turn off your AC at home when there is a threat of brown out /blackouts. Perhaps all cars should have a display that shows you how many gallons of gas per hour is being used by each accessory, as opposed to showing your change in mileage.
            Accessory              (gas consumption .01 gallons/hr)    
              AC                                        250                          
          4 DVD players                           95
     left turn signal that
    has been left on for the
    past 75 miles                                  10

    You pay as much for the privilege of air conditioning in a Prius as you would in another equivalently sized car with the same paint  and interior colors. Hint: get rid or your black car with the black interior.

    Economic justification: Right now, personally, it is probably hard to justify a Prius over an equivalently equipped econobox. Perhaps if one’s driving conditions optimally match the Prius, and if gas is expensive enough. I don’t think we know quite what the Lifetime TCO is on these things. Battery life is frequently brought up in these discussions, but CA requires they be warranted for 150,000 miles, that ain’t bad.  If you are a single commuter and you get to save time on your commute since you will be able to now drive in the HOV lane, it seems a no brainer if it only knocks 5-10 minutes off of your commute.

    To look at this from a different perspective. A lot of people pay a premium to have a high performance vehicle, higher acceleration, better cornering, higher top speed. Do you think that this extra performance reduces ones in transit time by even 2% over the lifetime of the vehicle. Probably not (with perhaps a few exceptions). You normally don’t see people complaining, “dammit, ya know, when I had that Nissan Sentra I couldn’t get over 85 MPH and my commute from Silicon Valley took 75 minutes, now with this Vette, it’s got a top speed over double that, and I only cut 2 minutes of my commute. WTF GM really misled me on this one.”

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