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100 MPG vs 10 MPG

Discussion in 'Gen 2 Prius Main Forum' started by flynz4, Dec 28, 2005.

  1. flynz4

    flynz4 Member

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    Being a newbie here... I wouldn't be surprised if this was posted before. I believe that it was discussed on NPR's car-talk, but I did not hear it first hand. Here goes:

    Scenario: You have two cars... one gets 10 mpg, and the other gets 100 mpg. Both are currently... and will continue to be driven equally

    What would be a better deal?

    a- increase the 100 mpg car to 200 mpg -or-
    B- increase the 10 mpg car to 11 mpg?

    The math is pretty simple... but the answer may not be intuitive.

    /Jim
     
  2. jimgraffam

    jimgraffam New Member

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    Not enough information to formulate a decision.

    1) How far is my commute?
    2) How much did I have to invest in each car?
    3) How long will I own each car?
    4) How cool is each car? (this one can and often does trump all others)
     
  3. hawkjm73

    hawkjm73 New Member

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    Well, the first car starts with costing 0.01 gallons per mile and goes to 0.005, with a savings of 0.005 gallons per mile driven. Car 2 starts at 0.1 gallons per mile and goes to 0.09 gallons, saving 0.01 gallons per mile driven.

    However, switching cars at the beginning saves 0.09 gallons per mile. Much better. B)
     
  4. 2Hybrids

    2Hybrids New Member

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    The better deal would be to dump that vehicle that gets 10 mpg....
     
  5. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    GM and I think Ford have used this argument to explain why it's better to bump their 10MPG vehicles to 11MPG than it is to do all the work to bump a 35MPG vehicle to 40MPG.

    But in the end, I agree with my hybrid brethren above: dump the 10MPG from the beginning or if you REALLY need both vehicles then for goodness' sake, don't drive the 10MPG vehicle so much. Because in the end, there are always two ways of looking at a problem:

    10MPG Vehicle
    Driven for 10,000 miles
    Consumes 1,000 gallons of gas
    Costs $2,250 assuming today's $2.25/gal

    100MPG Vehicle
    Driven 10,000 miles
    Consumes 100 gallons of gas
    Costs $225

    So now let's make the required modifications to the vehicles:
    11MPG Vehicle
    Driven 10,000 miles
    Consumes 909 gallons of gas
    Costs $2,045.50

    200MPG Vehicle
    Driven 10,000 miles
    Consumes 50 gallons of gas
    Costs $112.50

    A statistician would look at the numbers and point out that going from 10 to 11 reduced cunsumption by almost 100 gallons of gas while going from 100 to 200 reduced cunsumption by only 50. That statistician - being an intelligent, well-educated person - would then pack up her 200MPG vehicle and drive home.

    I always love a good mathematical and logic challenge. This is not one of them.
     
  6. daniel

    daniel Cat Lovers Against the Bomb

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    Sure, we know: cutting a 10 mpg car to 11 mpg saves more gas than cutting a 100 mpg car to 200 mpg. HOWEVER, it's the wrong question. The question that matters is, how much gas do you burn to meet your transportation needs. And the 100 mpg car burns almost no gas. So it's the better choice.

    Moving from a 10 mpg car to an 11 mpg car makes a bigger difference, but what you really need to do is put that car in a museum and start driving the 100 mpg car.
     
  7. Weinerneck

    Weinerneck New Member

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    This is exactly the kind of crap the current Republican administration (heavily involved in the oil industry) likes to see. They use stats like this to hammer there point that Hybrids are no good and the media runs with it. :angry:

    Only in Oil consuming America! :(
     
  8. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    I was digging around trying to find Bob Lutz's statement where he talks about what a great thing it is to boost the 10MPG vehicles to 11MPG. Instead - right now, anyway - I found this interesting tidbit about misrepresentation on GreenCarCongress.com:

    I just thought that was interesting. And it does apply to anyone: any manufacturer could very easily release a flex-fuel system (they are extremely popular in Brazil with sugar cane ethanol) and claim to achieve 100+ miles per gallon of gasoline. But how much would you trust a company who would try to pull it off?
     
  9. driveprius

    driveprius New Member

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    Just to set the record straight here's the algebraic solution to this word problem.

    Let G = gallons
    D = distance traveled
    M = mileage in mpg

    let M1 = older mileage
    M2 = newer improved mileage.

    The goal here is to get a formula that describes the amount of gallons saved with the incremental improvement from the older mileage M1 to the newer improved milage M2 going over the same distance D.

    We know from that G = D / M

    Let Gs = gallons saved

    Gs = (D / M1) - (D / M2) = (M2*D - M1*D)/ M1*M2 = D * (M2 - M1)/M2*M1

    So lets say we let both cars drive 100 miles every day. How much gas do we save for each car?

    Car #1:
    M2 = 200 mpg, M1 = 100 mpg
    Gs = 100 miles * (200 - 100)/(200*100) = 0.5 gallons saved

    Car #2
    M2 = 11 mpg, M1 = 10 mpg
    Gs = 100 * (11 - 10)/ (11*10) = 0.90909 gallons saved

    Answer: Improving car #2 saves us more gas than improving an already fuel efficient car #1.

    Conclusions: What the above math says is that if our nation is going to reduce fuel consumption there is much less need to try and invest more money in making a 50 mpg Prius go to 100 mpg. There will be more bang for the buck to start eliminating the least fuel efficient vehicles on the road. The math says that if you drive a vehicle that gets 15 mpg and decide to buy a bigger and faster vehicle that gets 11 mpg that seemingly tiny 4 mpg loss in mileage is going to start to become devastating to over gasoline consumption.

    The above math IS A VERY STRONG argument to obsolete cars that behave like car #2 and get more cars that behave like car #1. The above math is also a strong argument that if there are more vehicles that match the behavior of car #2 than car #1, then at this time you shouldn't bother trying to spend money getting car #1 to be better, because car #2 is hemorraging gasoline losses far worse and desparately needs to be improved.

    To make this more intuitive. Think of this as triage. You have several wounded coming in from battle. Should you put a better bandage on the person with a paper cut or concentrate your efforts on healing the person with open wounds on the verge of dying? In this day and age car #1 is like that person with the paper cut and he's bleeding gasoline, but only a small amount. Car #2 is like that person with open wounds gushing out gasoline. So what do you do? Obviously fixe up car #2. But simply going from 10 mpg to 11 mpg is not enough. That would be like putting a band aid over the person whose gushing blood. This bandaid will do nothing to save their life. The correct answer is to get car #2 improved from 10 mpg to 100 mpg so now car #2 is bleeding no worse than the wound of a paper cut. In other words you'll do much more to replace all those car #2's in the world with car #1's.

    Once we successfully replace all the car #2's with car #1's then we can revisit the issue of improving all the car #1's in the world from 100 mpg to 200 mpg.
     
  10. skruse

    skruse Senior Member

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    The NET effect, not the gross, effect must be considered. While mpg are a significant factor, emissions (efficiency) must also be considered. Example, a vehicle can reach 100 mph but at a very low efficiency rate.

    When you double efficiency you cut cost by one-half. Prius is designed to minimize emissions and reaps high operating efficiency as a byproduct. Detroit is stuck in the "substitute oil for knowledge" and "hit it with horsepower" mentality (i.e., most so-called Detroit "hybrids" do not reach the 45 mpg threshhold).

    Prius sets a high standard because it is AT-PZEV. The next step is PHEV ZEV (plug-in, zero emission vehicle). We need to develop a new concept of efficiency, i.e., "distance per Liter of electrons" (how far you can travel on a charge). A "Liter of electrons" does not exist which begs the next question: efficient batteries with greater capacity and longer life coupled with passive and active recharging (plug-in, integrated photovoltaic panels, regeneration, low mass carbon fiber bodies).

    When not in my Prius, I ride an aerodynamic carbon fiber bicycle (Trek 5200) with a frame that has a mass of one kilogram. I get more distance and less wind resistance for my effort.
     
  11. 2Hybrids

    2Hybrids New Member

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    then throw Car #3 into the equation...what would that be?
     
  12. efusco

    efusco Moderator Emeritus
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    Exactly.
    It's the wording of the question that affects everything. "Which has a greater impact on total fuel saved on a percentage basis?"--the change from 10-11, sure. But is that the right question to ask--is that question what is important? I don't think it is at all.

    Now, if we were, forever, going to be stuck with the same ratio of 10mpg vehicles and 100mpg vehicles, and fuel cost would never go up and fuel would never run out and emissions were not a concern, THEN the question above would be valid.

    But that is, clearly, not the case. The ratio of 10mpg and 100mpg vehicles will change with the increase in price of fuel which will increase with the proportion of 10mpg vehicles and decrease with the proportion of 200mpg vehicles...in a cyclical process. Overall cost of ownership will remain much cheaper and overall fuel consumption will be much lower with the higher mpg vehicle.

    Yes I understand the math here, but you have to make the question abstract to make the answer valid.
     
  13. driveprius

    driveprius New Member

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    Maybe. It seems my point wasn't taken clearly. In actuality the math DOES NOT contradict what is intuitive. Intuitively it just sounds right that we should dump the car the gets 10 mpg and drive home with the car that gets 100 mpg. And mathematically, you get to the same answer. So there is no trickery with statistics here. The answer is plain and simple if you had more HUMMER drivers trade in for a Prius the impact will be very big.

    Where the trickery comes in is to try and keep the bar of acceptable mileage as low as possible so it's real easy to make improvements. If you start with a low bar of gas guzzling, smog sputtering vehicles from the start then you can argue that money is better spent on making tiny changes to the worst offending vehicles. That type of argument would say you should see if you can sneak by with the manufacturing of cars with intentional gasoline leaks in their gas tanks so that you could later argue that money is better spent patching up the gasoline leaks than making an even more fuel efficient and cleaner Prius.

    So if you think of it correctly both the math and intution REALLY DO AGREE. THE MATH says to do the following:
    1) Do what you can to discourage the driving of any car that gets below 100 mpg. This means don't bother with the 10 to 11 mpg upgrade but go straight for the 10 to 100 mpg upgrade. This is a 1000% improvement. If you can make a HUMMER that gets 100 mpg than you don't need to trade in for a Prius.
    2) After you complete goal #1, then work on improving from 100 mpg to 200 mpg. This will be a 100% improvement.

    If you were to do #2 first and ignore doing #1 than you'll just create an exclusive group of high mileage drivers that get bragging rights. As an example there are a handful of people in this country that drive fuel cell cars. They get bragging rights of using no gas and achieving zero emissions, but it doesn't help you or I.

    Another sort of exclusive group are us, Prius drivers. We're a special crowd and we drive a car that's considered hip and trendy. If everyone drove a Prius today, we would lose that hip appeal, but the environment would be much better. I'd rather everyone else were able to get a Prius than for me to be able to brag about my 200 mpg super car.
     
  14. driveprius

    driveprius New Member

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    Car #3 would be the 200 mpg car or maybe the car that needs no gas at all.

    The math would say first get rid of all those 10 mpg cars and convince them to get car #3 with 200 mpg. If those 10 mpg drivers resisted than at least get them to drive the 100 mpg car.
     
  15. olends

    olends New Member

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    To really get into it, keep current carb rules, but add this little extra. what ever car has the highest mpg. every car that gets made withing 5 years, needs to be atleast 1/2 of that mpg.
     
  16. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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  17. bigdaddy

    bigdaddy Member

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  18. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    Well, you could --
    I mean, what if you --
    You could always --

    Oh crap.

    :lol:
     
  19. 2Hybrids

    2Hybrids New Member

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    slap on some chrome spinner wheels and I'd rock that Solectria!
     
  20. tripp

    tripp Which it's a 'ybrid, ain't it?

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    GRRR. :angry: We've been hoisted on our own statistical petard! :lol: