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Thread: CAFE standards for big rigs.

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by PzKfW IVe View Post
    Show this to be true.
    Compare the enegry used to overcome friction over a 20-mile struch of road comapred to the energy used to climb a 3% grade for that same 20 miles.
    Also, compare the energy used to overcome friction over 1/2 mile to the energy used to accelerate from a stop to 60MPH over that same 1/2 mile.
    In both cases, assume a 80,000 gross and 18 standard tires.


    Yes... altnough this adds to the price of a new truck.
    It also doesnt account for all of the existing trucks.


    As you are happy to confim - if there were an overall a cost benefit to these, they's be more widespread.
    Your idea forces compamies to spend money thay they won't bet back for the tunnel-vision goal of reducing fuel use.
    I’m a retired design engineer, mechanical, electronic computer HW & SW. So the first thing I do is to look at the problem that needs to solved. In this case you presented me with a problem that doesn’t need to be solved because of the magnitude of essentially level travel vs. climbing and descending. First I get to toss out the weight and the number of wheels. If it doesn’t work for a wide range of weights and wheels then it doesn’t work. So first I’ll define travel climbing and descending a 3% grade. Most trucks with a load can climb a 3% grade w/o decelerating much, but speed would be a consideration for aerodynamics. Tire friction loss mostly by the mile so its MPG effect is about the same regardless of speed. So I’m tossing out speed. On average trucks descend 3% grades as much as they ascend them, i.e. we don’t see them flying. A 3% down grade is not quite enough for a truck to roll w/o help from the engine. So the lower tire friction helps in both modes. Now the efficiency of the engine is greater climbing a 3% grade than descending a 3% grade, but that doesn’t matter much since it averages out to be just a bit less than level road. So what is left to calculate for? “Also, compare the energy used to overcome friction over 1/2 mile to the energy used to accelerate from a stop to 60MPH over that same 1/2 mile.” Easy, the incremental fuel used to accelerate to 60 in a half mile over driving at 60 for a half mile is huge; but not a big as I thought it was. I researched and found that a loaded 18 wheel truck runs at about 50% power, so up to 80%. So the truck will use about double the fuel. That will reduce the % saving from the ‘new’ tires by 50% during that ˝ mile. But, the amount of fuel saved for the ˝ mile by the tires is the same, therefore the payback for the new tires is in the same number of miles. Acceleration falls out of consideration. It also falls out for a more obvious reason, trucks don’t spend much time accelerating compared to driving at 65.
    I don’t think existing trucks are required to meet the new standards. Truckers will get back the investment in in fuel savings a new truck. The engineers have done their job. I’ve been in a similar engineering position myself with an entirely different product that had a recurring cost, but not fuel. Large very high-tech companies liked it.

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by Catawba View Post
    Now getting back to the OP, do you think it is technologically feasible to increase the mileage for tractor trailers by 2 mpg over the next 7 years as the standard actually calls for
    That's a 33% increase.
    Given that the weight and dimensions of the vehicles and the demenads these figures place on their drivertains will not change to any significant degree over the next 7 years, I'd say no.
    You, I am sure, will disagree. Specifically, why?

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by OhIsee.Then View Post
    I’m a retired design engineer, mechanical, electronic computer HW & SW.
    I see a lot of talk - but I don't see an answer to my question, especially given the way you redefined the situation to suit your position, and you distinct lack of specifics.
    Try again; show your work.

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by PzKfW IVe View Post
    That's a 33% increase.
    Given that the weight and dimensions of the vehicles and the demenads these figures place on their drivertains will not change to any significant degree over the next 7 years, I'd say no.
    You, I am sure, will disagree. Specifically, why?
    Because it is logical it can be done, and the experts, including the trucking industry agree! This has already been pointed out to you in this thread courtesy of Mattillac:

    http://www.debatepolitics.com/breaki...post1059724740
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    Re: CAFE standards for big rigs.

    [QUOTE=Catawba;1059750874]Because it is logical it can be done...[/qipte]
    It is logical... because it was done with cars?
    As I said before: Completeely different set of circumstances.
    You -continue- to make me laugh.

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by PzKfW IVe View Post
    It is logical... because it was done with cars?
    As I said before: Completeely different set of circumstances.
    You -continue- to make me laugh.

    Thanks for your opinion, we have decided to go with the experts who say otherwise!
    Treat the earth well: it was not given to you by your parents, it was loaned to you by your children. We do not inherit the Earth from our Ancestors, we borrow it from our Children. ~ Ancient American Indian Proverb

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by PzKfW IVe View Post
    I see a lot of talk - but I don't see an answer to my question, especially given the way you redefined the situation to suit your position, and you distinct lack of specifics.
    Try again; show your work.
    Your question doen't not apply to the issue. I explained that in detail. I'm open to have you show that an answer to your question would apply one way or the other to new design vs. old design tires. Or show why my answers are incorrect.

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by sawyerloggingon View Post
    Subject is MPG standards for big rigs, my post specifically addresses that, your post tries to change the subject. Typical lib,you try to obfuscate and deflect from the real subject . You guys do this as you get painted into a corner by facts and logic, happens every time. You also try to bait people into some petty argument to change the subject, nice try I won't bite. Troll somewhere else.
    Did you or did you not in the same ****ing post claim he's ignoring other factors while pointing out he talked about them?
    He touched her over her bra and underpants, she says, and guided her hand to touch him over his underwear
    Quote Originally Posted by Lutherf View Post
    We’ll say what? Something like “nothing happened” ... Yeah, we might say something like that.

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by OhIsee.Then View Post
    Your question doen't not apply to the issue.
    My question applies to your statement, specifically that more energy is used to overcome friction than to climb hills and change speed.
    The application to the issue is obvious.
    Show your work.

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    Re: CAFE standards for big rigs.

    Quote Originally Posted by Catawba View Post
    Thanks for your opinion, we have decided to go with the experts who say otherwise!
    It's pretty clear that you will go with whomever says what you want to hear, regardless of your competence to judge the soundness of what they say.

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