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Question About Differential Ratios

Discussion in 'Ask An Owner Operator' started by tdb, Dec 18, 2008.

  1. Dec 18, 2008 #1
    tdb

    tdb Light Load Member

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    Dec 18, 2008
    Canada
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    I've been researching drive trains for sometime to understand more thoroughly how spec'ing affects performance and fuel efficiency. I've learned a lot from technical articles, Cummins PowerSpec website, and a couple of really good trucking rags, but I'm still a little ignorant of differentials.

    Can anybody provide or refer some solid information on diffs? What do specs like 3.35, 3.90, etc, really mean? Are they ratios, like 1:3.35? If so, what does each figure of the ratio refer to? What is the consequence of the ratio? Does a low ratio provide extra power but lower top speed, while the inverse is true for a high ratio?

    If anyone, could sort this out for me, I'd appreciate it verty much.
     
    tdb, Dec 18, 2008
    tdb, Dec 18, 2008
    #1
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  3. Dec 18, 2008 #2
    MedicineMan

    MedicineMan Road Train Member

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    Jan 13, 2007
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    yes they are ratios as stated and it means the this
    3.55=the axle will rotate one time for every 3.55 times the diveshaft rotates
    4.11=one axle rotation for every 4.11 turns of the driveshaft.

    therefore the 4.11 will cause the motor to run higher RPM at the same MPH as the 3.55 would. THe 4.11 has the torque multiplication advantage since it takes less torque to turn the tires when you rotate the driveshaft more. the disadvantage would be poor fuel milage if you un higher speeds

    Gear ratios/tire size/transmission rations are all a fine balancing act between power and economy
     
    MedicineMan, Dec 18, 2008
    MedicineMan, Dec 18, 2008
    #2
  4. Dec 18, 2008 #3
    7mouths2feed

    7mouths2feed "Family Man"

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    Nov 29, 2007
    Jacksonville, AR
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    MM has set you on the right track. I have pm'ed you some more info that you should find helpfull.
     
    7mouths2feed, Dec 18, 2008
    7mouths2feed, Dec 18, 2008
    #3
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