Double Yellow's Company Driver to Independent Thread

Discussion in 'Ask An Owner Operator' started by double yellow, Nov 5, 2014.

  1. rollin coal

    rollin coal Road Train Member

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    The only right way to do an in frame is to do everything that could possibly need attention while you're at it. No way I'd let the bull gear go without replacing. I did a LOT of extras when mine went down and have no regrets about it at all. Cutting corners will cost you in the long run.
     
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  3. Old Man

    Old Man Road Train Member

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    I the bull gear goes down in the wrong place it could cost 120 -150 an hour plus a large tow bill. But you can probably get by till you have the reserves, are you doing the water pump or oil cooler? That can be done later
     
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  4. double yellow

    double yellow Road Train Member

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    Nope, not doing anything at the front of the engine. I wouldn't be as opposed to dipping into debt for elective preventative maintenance if there weren't so many big repairs still lurking on the horizon:

    1.6 million on the original meritor 10d transmission (which I plan to replace with eaton 13 sOD when it goes)

    1.6 million on rear end (which I plan on converting to a trailer axle + 23k single axle when it or front drive axle goes)

    1.6 milion on (unserviceable) meritor steer axle (which I plan on upgrading to a 13k+ axle when it goes).
     
  5. spyder7723

    spyder7723 Road Train Member

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    Wow. Do I ever need to open up an engine shop. It's an easy weekend job and an oem kit is about 2500. 8 grand for a Detroit. Holy smokes.
     
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  6. ReeferOhio

    ReeferOhio Medium Load Member

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    Well I feel a small part of your pain, clutch decided it wanted to go away today. I'm not sure if something broke but no clutch brake then I have a clutch brake, it started slipping really bad. So I limped it from Columbus Oh, back to Cincinnati. When it rains it pours.
     
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  7. ReeferOhio

    ReeferOhio Medium Load Member

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    Very good spec'ing. Mack just introduced a factory pusher axle I don't know if you caught it at MATS, which I think is the ideal set up for fuel economy. Have you researched replacing your 10B with a 10C? I do agree a 13spd is the best trans out there. IMO.
     
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  8. double yellow

    double yellow Road Train Member

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    Its great for short hauls where you go out loaded and return empty, but it isn't a good fit for OTR for the following reasons:

    1) Lifting a tractor axle outfitted with trailer tires will increase rolling resistance (assuming the drive axle has drive tires)
    2) A lift axle adds weight
    3) A tag axle is slightly more efficient than a pusher axle (shorter driveshaft)

    But for short hauls, you have the following advantages:

    1) Less tire wear
    2) Less rotating inertia -- a factor that becomes important the more rapidly & more frequently you accelerate
    3) Less tolls


    The 10C is the meritor 10speed overdrive? The 10 speed direct isn't bad -- I'd like it if 10th and 9th were just a little closer, but the gap between 8 and 9 really drops my speed uphill...
     
  9. ReeferOhio

    ReeferOhio Medium Load Member

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    I forgot you have a meritor the 10C is an eaton transmission, so is the 10B. The C basically is the overdrive where the B is not, the B is for the direct drive. I don't think I've every seen any spec with a 2.64 rear end with anything other than a 10B. I forget which ratio does it but with an 18B I believe eight direct will give you a direct drive as well, I'll have to go back and find that.
     
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  10. double yellow

    double yellow Road Train Member

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    The physics of MPG (part 1)

    I've been meaning to post this for a while, but it is one of those seemingly simple topics that has lots of special cases. But with people learning more and more about it from here, or KR, or the facebook 9mpg club, I think its time to go into a little more depth.

    This is the formula for power demand (ignore the constants, they are for cars):

    mpg equation.jpg
    Don't let the length of the equation throw you, it simplifies considerably if you stipulate steady speed (no acceleration) and flat ground:

    Power (flat ground, no acceleration) = m*v*g*Cr + 0.5*p*Cd*Af*v^3

    That's a little better, right? It can break down even more:

    Power (flat ground, no acceleration) = rolling power + aerodynamic power

    where rolling power = m*v*g*Cr

    and aerodynamic power = 0.5*p*Cd*Af*v^3

    And here are some generic constants for a semi truck and trailer:

    mass: 36287 kg (80,000 lb) -- this should be kg, not metric tonnes.
    velocity: 29 m/s (65mph)
    g: 9.8 m/s^2
    Cr: 0.0086
    p: 1.2 kg/m^3
    Cd: 0.7
    Af: 10.66 m^2 (13'6" x 8'6")


    How accurate is that formula?

    Most of you have probably seen this graph from the Cummins MPG whitepaper:

    power speed.png

    This is the EPA formula using the constants I provided:

    power speed23.jpg

    The only real difference between the two graphs is that Cummins separated tires from other rolling resistances (tires make up ~75% of rolling resistance).


    Factors that affect rolling resistance:

    m * v * g * Cr

    This is a linear equation, which means if you halve any of the terms, the result is cut in half. For instance, if you were to go from 80,000 lb to 40,000 lb, the rolling resistance power demand is halved:

    power speed32.jpg

    with aerodynamic drag:

    power speed42.jpg

    Likewise, if you cut your speed in half, you cut the rolling resistance in half... But what about g?

    G is a gravitational "constant," but it isn't 100% constant. In the USA it varies from 9.796 to 9.804 -- a ~0.1% difference. There isn't anything you can do about it, but you might as well know that rolling resistance is 0.1% less in Denver than New York City...

    Coefficient of rolling resistance? Now this is where modifications come into play.

    Tire rolling resistance of a typical truck:
    Steers: 110
    Drives: 140
    Trailer: 100

    That averages 118.5 -- (12,000 * 110 + 34,000 * 140 + 34,000 * 100) / 80000

    Using the lowest rolling resistance tires currently on the market brings that down to:
    Steers: 78
    Drives: 89
    Trailer: 75

    average: 81

    Which brings the overall coefficient of rolling resistance from 0.0086 to 0.00656:

    power speed52.jpg



    So what about a tag axle vs a pusher axle with a lift?


    Tag:
    Steers: 78 * 11,500 lb
    Drive: 89 * 10,000 lb
    Tag: 75* 10,000 lb
    Trailer: 75* 20,000lb
    ----
    average rolling resistance: 78

    Pusher with lifted axle:
    Steers: 78 * 11,500
    Lift: 75 * 0
    Drive: 89 * 20,000
    Trailer: 75 * 20,000
    ----
    average rolling resistance: 81

    But but but the man on the radio said lifting an axle lowers rolling resistance... He's wrong.

    But but but I saw a study of B-trains where they got better mpg lifting an axle... Those studies lifted a trailer axle, in which case it transferred weight among tires with equal rolling resistance -- it made zero difference in rolling resistance. What lifting an axle does do is removes 2 giant flywheels which lowers the rotational inertia making it easier to accelerate:

    mpg equation2.jpg

    ...but when velocity is constant, acceleration is zero which means that whole term gets wiped out (multiply something by zero and you get zero).

    If you are doing shorter hauls or are on roads with a lot of stoplights, this inertial factor can become significant. But if you accelerate once to 60mph and stay there for 5 hours at a time, it is essentially meaningless.


    But what about bearings?

    Remember that 75% of rolling resistance is tires, so of that initial 0.0086 coefficient of rolling resistance, 0.00215 of it is from bearings. Changing to synthetic fluids, for example, increases bearing efficiency by ~5% at 100F -- changing its contribution to the coefficient of rolling resistance from .00215 to .00204.

    Unfortunately, bearings are extremely efficient so that 5% improvement is imperceptible when looking at the big picture:

    power speed62.jpg

    Keep this in mind when listening to a salesman promise large mpg improvements if you switch to their magic bearings or lube.


    ... aerodynamics to come later
     
    Last edited: Jun 9, 2015
  11. Cranky Yankee

    Cranky Yankee Cranky old ######

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    i wish some of that was in english
    Dad was obsessed with mpg for years
    with his mercedes diesels
    he determined he could get 37 mpg never going over 52
    Mom finally quit riding with him
    she was sure she was going to get run over
     
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