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Thread: tire size makes RE ratio change how much?
          
   
   

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  1. 08-30-2010 12:35 PM #1
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    Dgas56
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    tire size makes RE ratio change how much?

     



    3:89 Re w 26" tall tires, but they are too narrow. So I want to put on 275 60 15's which are 28' tall. Clearence on the car is not an issue there is plenty. given the added dia. I am sure rpm will decrease some. Which will not break my heart. Those 3:89's make the engine howl pretty good at 70 MPH (459 dyno'd w drivetrain load HP). But how much will the added 2" change it?
    Last edited by Dgas56; 08-30-2010 at 12:38 PM.
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  3. 08-30-2010 12:40 PM #2
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    skids72
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    the difference will be proportional to the change in tire diameter: 3.89:1 with 28" tire = 3.61:1 with 26" tire.... at the same MPH, the RPM will drop 13/14ths (26/28ths).

    -Chris
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  4. 08-30-2010 12:50 PM #3
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    rspears
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    Skids typed quicker than me With your 3.89's and no OD (1:1 final tranny output) you'll turn 3519rpm at 70mph with 26" tires, and 3268rpm with 28" tires which is indeed exactly 13/14th's change.
    Roger
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  5. 08-30-2010 08:51 PM #4
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    randyr
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    Here's a great little calculator to figure it out..http://www.ringpinion.com/Calc_RPM.aspx

    Plug in all the different combos you want and see how it changes your rpms....
    "It is not much good thinking of a thing unless you think it out." - H.G. Wells
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