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Direct drive OR lower RPM

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Oram, Nov 1, 2012.

Page 1 of 4
  1. Nov 1, 2012 #1
    Oram

    Oram Medium Load Member

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    Jan 28, 2012
    WINDSOR, ON, CANADA
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    I am doing the specification for my new truck. My big dilemma right now:
    The new 2013 Cummins has a lower sweet spot, the maximum torque now available at 1000RPM, so at my cruising speed, at 61mph it would run at 1150RPM. My original plan was, to have a direct drive transmission, what could save me 1.5-2% fuel because of the less parasitic loss. But, because there is no fast enough rear gear ratio, my RPM would be 1300RPM. So I have to choose. Lower my cruising RPM by 150RPM, or have a direct drive transmission.
    (I run upper Mid States and Ontario, max 80,000lbs, 99% highway, dry van.)
     
    Oram, Nov 1, 2012
    Oram, Nov 1, 2012
    #1
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  3. Nov 1, 2012 #2
    bender

    bender Road Train Member

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    Jul 20, 2010
    Don't Kid Yourself
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    What about tire size to tune with?
     
    bender, Nov 1, 2012
    bender, Nov 1, 2012
    #2
  4. Nov 1, 2012 #3
    black_dog106

    black_dog106 Road Train Member

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    I believe Schnieder/JB etc are running rears in the mid 2's ratio now?:biggrin_25524:
     
    black_dog106, Nov 1, 2012
    black_dog106, Nov 1, 2012
    #3
  5. Nov 1, 2012 #4
    bender

    bender Road Train Member

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    Don't Kid Yourself
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    2.64's, direct trans and tall rubber. How's that come out for rpm's at your 61 mph road speed?
     
    bender, Nov 1, 2012
    bender, Nov 1, 2012
    #4
  7. Nov 1, 2012 #5
    ghf

    ghf Bobtail Member

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    Oct 2, 2012
    Seattle, WA
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    I spec'd a truck quite a while back with a 3406B. I went with a double OD, and higher rear end ratio. When I was on the flats, I was just a bit above idle, but when I pulled a grade I had the higher rear ends for better torque multiplication. My truck was very similar to some company trucks, except they had lower rear ends, and direct drives. I out pulled them on the hills and got better mpg. The disadvantage with this is more drag and heat, but watch your guages and drop a gear. Hope this helps.
     
    ghf, Nov 1, 2012
    ghf, Nov 1, 2012
    #5
    Oram Thanks this.
  8. Nov 1, 2012 #6
    allan5oh

    allan5oh Road Train Member

    1,557
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    Jan 6, 2010
    Winnipeg, mb
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    What gear ratios and road speeds are we talking about here?

    What is the sweet spot on the new cummins? Max torque is 1000, but I assume cruise speed is 1150 like you said?


    2.47 gears and 11r22.5 tires gives a cruise speed of 1225 at 60. Low profile is 1267 RPM. I would go with that and a direct drive.
     
    allan5oh, Nov 1, 2012
    allan5oh, Nov 1, 2012
    #6
  9. Nov 1, 2012 #7
    Oram

    Oram Medium Load Member

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    Jan 28, 2012
    WINDSOR, ON, CANADA
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    I can not really operate with tire size, because I want to go with SS tires. That saves around 4%, so it would not worth to sacrifice it for 2% saving. There are companies, who use direct drive transmission, but usually they run with higher cruising RPM, because the company drivers complain, if they have to change gear to often. But as an O/O, every cent counts. Now, the 2.5 is highest available rear, that brings down my RPM to 1300.
     
    Oram, Nov 1, 2012
    Oram, Nov 1, 2012
    #7
  10. Nov 1, 2012 #8
    Oram

    Oram Medium Load Member

    452
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    Jan 28, 2012
    WINDSOR, ON, CANADA
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    The sweet spot from 1000-1500RPM. The cruising speed is optional from 1150-1600.
    Yes, the Meritor 14X has 2.47, but this is tandem, and I will go with one drive, one dead axle. The meritor Fuelite has only 2.5, but Paccar do not has it. The Dana S23-190 comes with 2.53 fastest.
     
    Oram, Nov 1, 2012
    Oram, Nov 1, 2012
    #8
  11. Nov 1, 2012 #9
    chalupa

    chalupa Road Train Member

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    Jul 22, 2010
    Houston,Texas
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    Highest available from who? You can buy any ratio you want. Isn't Wally running a 2.32 / 10D / Cummins ISX ? Anyone know what MVT runs? Has to be good for the fleet to avg. 9.5.......
     
    chalupa, Nov 1, 2012
    chalupa, Nov 1, 2012
    #9
  12. Nov 1, 2012 #10
    allan5oh

    allan5oh Road Train Member

    1,557
    556
    Jan 6, 2010
    Winnipeg, mb
    0
    Dead drive axles are legal in Ontario?

    I know they aren't out west.
     
    allan5oh, Nov 1, 2012
    allan5oh, Nov 1, 2012
    #10
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