Ratios

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Raider, Feb 12, 2010.

  1. Raider

    Raider Bobtail Member

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    Dec 24, 2009
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    OK here it goes!
    When I buy a truck I am looking for power enough to do the job but not major overkill. So I am thinking 475-500 HP 18 speed trans. My biggest question is what is a good gear ratio for this combo? I want to be able to drive flat lands and mountains. In my head I'm thinking 3:55- 3:70. but I need some experts advice.
    many thanks
    Raider
     
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  3. Longhood379

    Longhood379 Medium Load Member

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  4. Jfaulk99

    Jfaulk99 Road Train Member

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    what brand engine and what size wheels/tires changes what ratio you'd need.
     
  5. groundpounder

    groundpounder Road Train Member

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    I always bought my Petes with Cat's (475hp minimum), 18 speeds, and 3:55 ratios...I thought that combo worked pretty well, now keep in mind I got out of the O/O biz back in 2001 so things may have changed as technology has advanced and I have not kept up with all that..

    I still read truckpaper once in a while and seems I see a lot of 18 speeds with 3:36 rears FWIW..

    good luck !!
     
  6. lovesthedrive

    lovesthedrive R.I.P.

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    3.70 is good horse power but moot point for a 18 speed. Stick with lower ratios.
     
  7. Raider

    Raider Bobtail Member

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    Dec 24, 2009
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    Many thanks for the Replies!!!
     
  8. melpromud

    melpromud Medium Load Member

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    I have a isx cummins 530 hp 18sp. with 3.91s and 11r 24.5s. I run up to 107,000 LBS on up to 12% grades and its perfect. At 80,000 OTR I would want 3.55s or 3.36s although 3.70 or 3.73s would be ok if you plan on running slow.
     
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