3.55 vs 2.85 Gear Ratios

Discussion in 'Peterbilt Forum' started by MellowTrucker74, Jun 28, 2022.

  1. MellowTrucker74

    MellowTrucker74 Bobtail Member

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    Hello friends... First time truck buyer and I'm debating between a 2015 579 with 3.55 ratio and a 2016 579 with 2.85 ratio. Both have the ISX 15 and Both have about the same miles (600k) . There's a difference in price, the 2.85 is 15k less.

    I've read that lower ratios would impact my towing capacity and that the best all around would be the 3.55. I would like to hear your thoughts specially if you drive one with the 2.85 at how it handles the heavier loads.

    Thank you in advance.
     
    beastr123 Thanks this.
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  3. beastr123

    beastr123 Road Train Member

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    It depends on the transmission. The 3.55 gears with a 10,13 or 18 speed transmission will run as fast as the 2.85 gears with a direct drive transmission. The difference is in the "startibility" or lift in the lowest gear in each. The 2.85 will not transmit the torque to the ground as well.
     
  4. Cat sdp

    Cat sdp . .

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    Any difference in the Trans and tires ?
     
    Magoo1968 and RockinChair Thank this.
  5. Magoo1968

    Magoo1968 Heavy Load Member

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    2.85 will likely be direct drive or single over .if it’s direct that equates to about a 3.70ish with a double over trans like the 3.55 will have . So it would have better start ability than 3.55 due to the steeper gear ratio in transmission.
     
    Big Road Skateboard Thanks this.
  6. TruckerPete1990

    TruckerPete1990 Road Train Member

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    What transmission? 3.55 is such a outdated gear on these newer trucks. That would be a 2350 isx peak torque is 1200-1400 anything over is a fuel killer
     
    MellowTrucker74 Thanks this.
  7. MellowTrucker74

    MellowTrucker74 Bobtail Member

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    Jun 28, 2022
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    Thank you for your response. The 2.85 has an Eaton Fuller 10 speed auto shift. Being a rookie I do not want to invest in an under powered rig. I want something that is versatile enough for 40-45k pounds hauls.
     
  8. MellowTrucker74

    MellowTrucker74 Bobtail Member

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    I guess my question is with a 2.85 would I be able to manage most loads and still retain some fuel efficiency?
     
  9. MellowTrucker74

    MellowTrucker74 Bobtail Member

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    Jun 28, 2022
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    Thank you for you all input. I finally went with a 2017 Pete. 10 speed automatic and 3.08 gear ratio and a 238 wheelbase. I'm very excited to get to work on it!!
     
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