1. Runner71

    Runner71 Well-Known Member

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    So.. Is this correct?
    20200920_180759.jpg 20200920_180827.jpg

    Swapped from 3.23 to 3.91 then from 275/60-15 (28") to 295/50-15(26.6")

    So with the 3.91 and 26" its more like 4.11?
     
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    • MoparLeo

      MoparLeo NRA PATRON LEVEL LIFE MEMBER FBBO Gold Member

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      Yes. Have fun on the Hi-way.
       
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      • #41

        #41 Well-Known Member

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        No - gear ratio is gear ratio, then the tires are driven. Then tire diameter can effect RPM.

        It's all relative anyway. The original tire diameter on your car was closer to 26", so switching from a 28" tire to a 26" inch tires is really like 3.91 was if you car happened to originally come with that gear.
         
      • 33 IMP

        33 IMP Well-Known Member

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        Changing to a shorter tire will make a car act like it has a lower (higher numerically) gear. So yes, your shorter tire with 3.91s will ACT like 4.10s with 28/29"tall tire. If you decide you have gone too far with the gear swap, a fat 75 aspect tire can change the "effective" ratio back down/less rpm on the highway.
         
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        • Fran Blacker

          Fran Blacker FBBO Gold Member FBBO Gold Member

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          3.91 to 4.10 are fun gears if you seldom go more than 50 mph (80 kmh). Higher speeds unless you have OD is a drag.:D:rolleyes:
           
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          • Runner71

            Runner71 Well-Known Member

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            I have the 3.91's installed - been driving it since may and like it...but it's just that i build the engine and tuned for alot of bottom torque and snappyness and sometimes it feels like i need more gear ratio so the engine have more to work with? I never need to use First gear. and i can shift from first to fourth and start on third without even notice it!
            And i have a complete 89 house with a 3.23 in it, mayby it will give the engine more to work with?

            440, 4spd
            Milled 452's to closed chambered 79cc
            Hugh whiplash installed @ centerline 160-5 psi in cyl pressure
            Lockedout @ 37 tot / 15hg merc

            Little fun.

            Start.
             
            Last edited: Sep 20, 2020
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            • Runner71

              Runner71 Well-Known Member

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              Or should i keep the 3.91 and go with a taller tire again, like 28-30" anyone with experience?
               
            • 33 IMP

              33 IMP Well-Known Member

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              If I had a 71 runner with 3.91s, I would run the absolute tallest tire I could fit in the wheel well, a 285/70x15 if it fits. 30 1/2 tall.
               
            • Runner71

              Runner71 Well-Known Member

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              Yeah, think thats my mistake..wasn't paying attention at sizes and how it affects. Gonna take the life out of these ones and order me some 28 - 30" inches tall depending on whats fits!
               
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