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Thread: rear end ratio

  1. #1
    Senior Member smokensteve's Avatar
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    rear end ratio

    could someone please explain to me what the numbers mean, when talking about rear ends...like 3:40--3:70..etc...and what they mean in terms of highway driving and RPM's on the highway...thanks...I believe mine are 3:42 in my truck, 5th gear runs about 2000 RPM's @ about 70 mph

  2. #2
    Senior Member mrjohnwayne's Avatar
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    the numbers correspond to the revolutions of the drive shaft compared to the tire. If you have a 3.73:1 rear end ratio, that means that the driveshaft/pinion gear will spin 3.73 revolutions to the 1 revolution of the tires/ring gear.

    when talking about gear sets they are backwards. the higher the number the lower the gear and vice versa.

    3.42 is a "high" gear whereas 4.10 is a "low" gear

    Higher gears are good for highway use and all out speed. but are terrible for pulling and take off.
    lower gears are good for pulling (it acts as a torque multiplier) and getting out of the whole but are terrible for top end.
    John Wayne

    2000 F-350 7.3L Powerstroke 4x4

  3. #3
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    bradrhale's Avatar
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    might i add also that the lower the gear(higher numerically) will increase your engine RPM overall. you have 3.42 gears so if you went to 3.73, you would be turning around 2200 or 2300 RPMs at versus what you are running at now. this will work the opposite way as well.

  4. #4
    Senior Member smokensteve's Avatar
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    Kewl...thanks alot for the info, exactly what I was looking for..

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