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Need help figuring out speed after regearing

Discussion in '80-Series Tech' started by Panzer, Mar 5, 2007.

  1. Panzer

    Panzer SILVER Star

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    With the stock gears and 315's 65mph indicated was about 72mph actual.
    Now I am running 4.88's and have no clue now of my speed.
    I know the 4.88's underdrive me for the the tire size so I am guessing that 65 indicated now is about 60 mph.

    Anyone know the real answer?

    TIA,
    CAS
     
  2. DanKunz

    DanKunz SILVER Star

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  3. Romer

    Romer fatherofdaughterofromer Moderator

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    If I recall, the 4.88's and 315's are 8% slower than the odometer says you are going.
     
  4. landcrusher80

    landcrusher80

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  5. Mark W

    Mark W

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    RPM multiplied by the overdrive ratio, divided by the differential ratio, multiplied by the actual tire diameter (in inches), multiplied b Pi, divided by 12 multiplied by 60 divided by 5280.

    True mph.


    Mark...
     
  6. MTNRAT

    MTNRAT SILVER Star

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  7. landtank

    landtank SILVER Star

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    I used the 8% value when I originally adjusted my truespeed. 5 years later I checked it with my GPS and is was right on.
     
  8. Panzer

    Panzer SILVER Star

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    8% SWAG is good enough for now.
    thanks for the assistance