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Thread: 4.88s with 40s and 4:1 tcase

  1. #1
    Been Around the Block Braxtonsag's Avatar
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    4.88s with 40s and 4:1 tcase

    Before I get screamed at about how 5.38 is the correct ratio for 40s hear me out.

    I bought my jeep with 3.21s and 29Ē tires and I really didnít mind the way it drove. It had plenty of power and got the job done. Fast forward a bit and I was eventually running 4.88s with 37s. I kind of despised how over geared the jeep felt and moving up to 38s was a breathe of fresh air although it still feels a bit over geared on the highway. Iíd like to move up to 40s and going by the infamous jk gear ratio chart I would STILL be overgeared compared to how my jeep came stock.

    The only downfall to this is that I think with my sport tcase, 4 low wouldnít be ideal and I would need to source a rubi tcase. On the brighter side, Iíll have much more pinion to play with than on a 5.38 in my dana 44s. Iím fully aware dana 44s arenít the ideal axle for 40s but Iím more of an explorer rather than a hardcore rock crawler. They will suit me just fine.

    Anyone have any input on this gear and tire combo? Should I stick to this plan or bump up to a 5.13? Probably going to be a matter of opinion but wanted some insight from you guys anyways.

    Iíll attach the gearing chart and I have circled how my jeep came, where it is now, and where it will be after 40s.

    3FAFA41A-C4C5-456B-9D3E-4814AFC88575.jpg

  2. #2
    Old Timer fiend's Avatar
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    Sounds like youíre pretty confident 4.88s will be fine. Why not give it shot. You can always regear later.


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  3. #3
    Knows a Thing or Two danford.lau's Avatar
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    Quote Originally Posted by Braxtonsag View Post
    Before I get screamed at about how 5.38 is the correct ratio for 40s hear me out.

    I bought my jeep with 3.21s and 29Ē tires and I really didnít mind the way it drove. It had plenty of power and got the job done. Fast forward a bit and I was eventually running 4.88s with 37s. I kind of despised how over geared the jeep felt and moving up to 38s was a breathe of fresh air although it still feels a bit over geared on the highway. Iíd like to move up to 40s and going by the infamous jk gear ratio chart I would STILL be overgeared compared to how my jeep came stock.

    The only downfall to this is that I think with my sport tcase, 4 low wouldnít be ideal and I would need to source a rubi tcase. On the brighter side, Iíll have much more pinion to play with than on a 5.38 in my dana 44s. Iím fully aware dana 44s arenít the ideal axle for 40s but Iím more of an explorer rather than a hardcore rock crawler. They will suit me just fine.

    Anyone have any input on this gear and tire combo? Should I stick to this plan or bump up to a 5.13? Probably going to be a matter of opinion but wanted some insight from you guys anyways.

    Iíll attach the gearing chart and I have circled how my jeep came, where it is now, and where it will be after 40s.

    3FAFA41A-C4C5-456B-9D3E-4814AFC88575.jpg
    Might be only person Iíve ever heard say 4.88 with 37s is over geared . Itís what I run and while itís fine .. certainly not over geared



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  4. #4
    Been Around the Block Braxtonsag's Avatar
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    Quote Originally Posted by fiend View Post
    Sounds like youíre pretty confident 4.88s will be fine. Why not give it shot. You can always regear later.


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    Yeah I guess it actually is that easy now that you put it that way 😂 nothing to really regret purchasing or doing
    Quote Originally Posted by danford.lau View Post
    Might be only person Iíve ever heard say 4.88 with 37s is over geared . Itís what I run and while itís fine .. certainly not over geared



    Sent from my iPhone using WAYALIFE mobile app
    Iv talked to a lot of guys on here and they all seem to agree with you lol. I donít know if itís just because Iím in indiana and itís ALOT of highway miles to get anywhere fun to explore or what, but I gained like 2mpg just switching from 37s to 38s. No way in hell Iíd go back to a 37 on these gears if I ever had to travel long distance again.

  5. #5
    Nothing but a Thing desertrunner's Avatar
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    Quote Originally Posted by danford.lau View Post
    Might be only person Iíve ever heard say 4.88 with 37s is over geared . Itís what I run and while itís fine .. certainly not over geared



    Sent from my iPhone using WAYALIFE mobile app
    Haha that was exactly my thought running 4.88s and 37s. Shoot I even have a Rubi 4:1 tcase and I wish I had 5.13s

    Honestly OP I agree with above if you think your 4.88s and 38s works then try it with the 40s....why not worst comes to worst it will be a little gutless but it will still drive.

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  6. #6
    Old Timer bkac's Avatar
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    I personally love 5.38s and 37s. The 3.6 loves high rpms and runs hotter then most engines.


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  7. #7
    Been Around the Block Braxtonsag's Avatar
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    Quote Originally Posted by bkac View Post
    I personally love 5.38s and 37s. The 3.6 loves high rpms and runs hotter then most engines.


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    Omg lol I literally couldnít even imagine that combo

  8. #8
    Addict Ddays's Avatar
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    There's a reason no one runs 4:88's on 40's. Your Jeep will accelerate like a slug.
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  9. #9
    Old Timer Clutch's Avatar
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    some people run 37s with 3.21s and donít mind, so maybe 40s with 4.88s will pass the test for you?


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  10. #10
    Been Around the Block Braxtonsag's Avatar
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    Quote Originally Posted by Ddays View Post
    There's a reason no one runs 4:88's on 40's. Your Jeep will accelerate like a slug.
    Do you think my jeep only weighing 4500 lbs would have anything to do with me being perfectly fine with 4.88s and 38s?

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