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XJ on 31s? MPG? Re-gear worth it?

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  • #1

    XJ on 31s? MPG? Re-gear worth it?

    I've been out of the jeep world for a couple years. Picked up an XJ a couple weeks ago and I need to do some suspension work. Since I'm already there, it's time to grow a little. I'm trying to decide between 2" of lift and 30s vs 3" and 31s. I have a couple questions.

    I know we don't buy these refrigerator boxes on wheels for their gas mileage, but what kind of gas mileage are you getting with stock gears, auto, and 31s? I know it's subjective, but what are your thoughts on needing to re-gear at 31s? Does it hold speed ok on the highway, or downshift on every incline?

    Thanks!
    Toby
    Tags: None
  • #2
    I installed 4.88s when I got 3"lift and 31s ! Was great ! I went up to 34s and wished I had 5.38s ! They, unfortunately, dont make 5.38s for hp 30 front axle ! :( I am going to install 5.38s in axles I have now (hp44 and ff60) but with an overdrive tranny and big tyres, it aint bad !
    I may be Rad and I may be Bad :pbj: but I am never SAD ! :kilt:
    Yea I'm *Q*C* and ?
    it is a great feeling to have served your country and walk PROUD
    Yes veterans stand tall and their shadow protects all !

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    • #3
      What gears does it have in it now? 3.07 or 3.55..........
      -Mike B-
      '01 XJ Sport
      '11KK Limited

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      • #4
        It currently has 3.55s. I thought the 3.07s were just in the 5spds.

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        • #5
          ^^^ That was my recollection as well regarding 3.07s - but I asked since you were talking about regearing. I really would think the stock 3.55s would be fine with the 31" tires. I haven't regeared my 3.55s running 33s - granted I'm not exactly concerned with road manners or mpg's. I'd love to step-up to 4.56 or 4.88s to slow my crawl.
          -Mike B-
          '01 XJ Sport
          '11KK Limited

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          • #6
            With my '98 4.0l, Ax15, The MPG was the same at 2" and 3" with 30s, About 20ish. You could feel that there was a taller tire then stock, But I don't think that 31s would be a problem. I am planing on some 245/75R16s soon.

            FWIW I just sold a '01 4.0l, auto, with 3" and 31s and It didn't feel like it lost much power still running the 3.55 ratio. It did have the MOPAR performance headgasket tho.

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