Good rear axle ratio?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Slingingbullets, Sep 22, 2014.

  1. Slingingbullets

    Slingingbullets Bobtail Member

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    Sep 19, 2014
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    I'm looking at at KW T680 with Cummins ISX15 rated at 485hp with 13spd and 3.36 rear axle. I typically pull avg of 37-41k. I run mostly midwest with some runs going through the appalachians. I'm wondering if that's going to be a good balance of mpg and pulling power. I would love to get 6.5ish but still take the hills pretty well.
     
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  3. Pahrump

    Pahrump Medium Load Member

    good ratio sweet spot is around 1500 to 1600 rpm
     
  4. Richter

    Richter Road Train Member

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    what speed do you plan on running? unless you go 70+ you would be better with a 3.55. What kind of tires? Is your 13 a double over or single over? Without the above info, no one can make a 100% accurate recommendation. Short rubber with a 3.36 is roughly the same as a 3.55 with tall rubber, although id recommend short ruber with a 3.55 unless your planning on going 70 all the time.
     
  5. Slingingbullets

    Slingingbullets Bobtail Member

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    Sep 19, 2014
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    Tires on it are 275/80R22.5 , tranny is 13 double over, 65-68 mph ave cruising speed
     
    Last edited: Sep 22, 2014
  6. Richter

    Richter Road Train Member

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    Feb 13, 2012
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    Slingingbullets Thanks this.
  7. Richter

    Richter Road Train Member

    4,090
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    Feb 13, 2012
    Philadelphia Pa
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    what rpm do you want to cruise at...i feel 1600 is a bit high for that motor.
     
  8. Slingingbullets

    Slingingbullets Bobtail Member

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    Sep 19, 2014
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  9. mattbnr

    mattbnr Road Train Member

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    Slow down to 60 and you'd gain 1 mpg right there with no changes. Every 1 mpg over 55 you lose .1 mpg.
     
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