37" Tires on a new Gladiator Rubicon

  1. Glad4life

    Glad4life Member

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    Hello all,

    Planning to mount 37's on and need some advice.

    I want to keep all the stock pull capability. I will be towing at least 6000-6500 lbs 5-6 times a year.

    Truck will get 5000 miles a year.

    Planning on a lift as well.

    Stock Rubicon has 4:10 gears.

    I still want to run it on the trails. Medium stuff, I am not planning anything wild.

    Question 1. What is the best gearing to put in the axles for the 37's? 4.88 or 5.13?

    Question 2. Do I need to take the truck to Jeep and have some reprogramming done? If so, what am I suppose to ask them to do and what can I expect this service to cost?

    Thank you in advance.
     
  2. Carlton

    Carlton Well-Known Member

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    If towing often I would stay with the stock set up. However, of you are set on the 37s I'd go 5.13. You can go to the dealership for a reprogramming but I would suggest getting a FlashCal or Tazer. These will allow you or the shop to reprogram for the tires and gears plus added features.
     
  3. TennesseePA

    TennesseePA Well-Known Member

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    doing a rough calculation to keep the same gear ratio you would need to regear to about 4.56. The math is quite easy (37/33) * 4.1 = 4.59. Now that is just using published tire diameter so it is not 100% accurate but pretty close.
     
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  4. RedTRex

    RedTRex Well-Known Member

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    Hey that is pretty nifty calc
     
  5. beelzebot

    beelzebot Well-Known Member

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    Agreed on just getting your own programmer. My dealer quoted $125 for all of the recalibrating, but I've seen as high as $250 in some places.
     
  6. SKT

    SKT Well-Known Member

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  7. SKT

    SKT Well-Known Member

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  8. since41

    since41 Well-Known Member

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    so if you flip the (33/37) * 4.1 = 3.66
    Assuming that is the near gearing when jumping to 37s?
     
  9. OP
    OP
    Glad4life

    Glad4life Member

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    Thanks all for the feedback. 4wheel parts suggested 4:88 gears and they will provide a Speedo recalibrator. Is that what you all are referring too that needs done after changing to 37’s?

    Currently in Flagstaff for overland expo west. Big surprise this was happening on my way home.

    1B009076-F1FD-4C41-A0C3-99E2709A4FB5.jpeg
     
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  10. TennesseePA

    TennesseePA Well-Known Member

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    That is correct
     
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  11. Ole Cowboy

    Ole Cowboy Well-Known Member

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    If you are wanting 37's then go with 4:88's. 5:13 are getting a bit on the steep side and even with 37's you are going to be spinning some rpm on the highway. 4:88 should keep you inside the cooling envelope of your JT, its also one of the strongest gearsets so it will take the street, miles and off road without issue. Jeep has beefed-up that D 44 axle set and if you keep your tires balanced and rotated you should see good life out the upgrade.

    TIP: Big jump in tire size, so it begs the question: How much air pressure do I run? First, every tire is different, when I ran BFG KM2's I ran 16 psi so how did I arrive at that? Find an empty parking lot with a puddle of water or a dusty road you can pull off on.

    Tires are all about 1 thing, the Contact Patch and they are meant to have a full contact patch or you can wear out the center of the tire (too much air), wear out the outer edges (not enough air), your air pressure needs to be set at Goldilocks, not too much, not too little.

    Drive-thru water onto dry pavement and look at the tracks, it will show the contact patch adjust air pressure till you go Goldilocks. Drive onto a dusty road and stop, look at the dust on the tire another way of seeing what your contact patch looks like. It may take several outing to find it.

    Door jamb air pressure is based upon the OEM tire and F/R weight of the vehicle, change the size of the tire and you must change the AP. REMEMBER: The Tire does NOT care what AP you run as long as it gets it's happy contact patch.

    FYI . Where did I get this info. Growing up on the ranch we had a lot of rolling vehicles. I learned from my dad, that is how it was done back in his day, tire pressure gages were few and very far inbetween, $$$ to boot and inaccurate.

    To this day every time I drife thru water or dust when I stop I look at my tires and contact patch...
     
  12. homerun

    homerun Well-Known Member

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    Chalk works just as easily.
     
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