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Thread: Gear Ratio

  1. #1
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    USAF Gear Ratio

    What would be the best gear ratio for a 2005 wrangler, with 4.0, atomatic w/overdrive and 33" tires. Jeep is daily driver and off the road maybe once a month, mud and trails.

    Thanks

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    No Mas Jeepalonie
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    4.56
    Jeepless Again

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  3. #3
    Senior Member SavageSun4x4's Avatar
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    Age old question:

    Where you would like to fall is in the "black" zone.
    The "blue" zone is going to possibly affect your highway MPG and have you turning a few more RPMs than you may desire.

    The "yellow" zone may not give you enough highway RPMs but most likely give you better low-end grunt.

    You will want to factor in your engine's torque and horsepower band to get better use of this chart.

    Jeep 4.2/4.0 L I-6:
    Horsepower (net) 185 @ 4750 +/-
    Torque (net) 220 @ 4000 +/-

    Jeep 2.5 L I-4:
    Horsepower (net) 123 @ 5250 +/-
    Torque (net) 139 @ 3250 +/-




    rpm_chart-2.jpg


    What I would tell you is: If you are ABSOUETLY POSITIVE you will never go beyond a 33 in tire then the 4.10 ratio would be perfect. But go beyond that and in tire size and you will wish you had gone to a deeper ratio.

    So if you MIGHT go bigger, but not sure when or how big then I would go with 4.88's







    Don

    '15 Jeep Unlimited Rubicon Hard Rock...OLD SCHOOL 6 Spd Manual Trans
    17 Oaks Ranch Companies LLC

    www.savagesun4x4.com

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    Well I just got my new tires put on today. And next weekend will be swapping gears. Going to 35's with 4.88's; puts me in the black zone (And I hadn't seen one of these charts previously, lucky me) Unfortunately, I will be running my current 3.73's until then which puts me below the yellow zone. Should be a long slow drive to and from work tonight and all next week
    06 LJ | 4.0L | NSG-370 | D44/D30 w/4.88's | 4.5" RE Superflex lift | 35-12.50-15 Cooper STT's on 15x10 Cragan steelies | RockKrawler X-Factor steering | Shrockworks sliders | DirtWorx bumper/tire carrier | LockRite auto locker | Midland CB w/4 ft Firefly antenna | SOLID rear diff cover | DIY thumb throttle | 750w power inverter | Smittybilt XRC8 winch ...and GROWING








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  5. #5
    Senior Member SavageSun4x4's Avatar
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    you are doing good with the 4.88's
    Don

    '15 Jeep Unlimited Rubicon Hard Rock...OLD SCHOOL 6 Spd Manual Trans
    17 Oaks Ranch Companies LLC

    www.savagesun4x4.com

  6. #6
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    they won't be in till next weekend. Currently have 3.73's till I can swap next weekend. But the 4.88's will be nice when done
    Last edited by Scooter LJ; 04-22-2011 at 19:36. Reason: spelling
    06 LJ | 4.0L | NSG-370 | D44/D30 w/4.88's | 4.5" RE Superflex lift | 35-12.50-15 Cooper STT's on 15x10 Cragan steelies | RockKrawler X-Factor steering | Shrockworks sliders | DirtWorx bumper/tire carrier | LockRite auto locker | Midland CB w/4 ft Firefly antenna | SOLID rear diff cover | DIY thumb throttle | 750w power inverter | Smittybilt XRC8 winch ...and GROWING








    http://wheelersforthewounded.org
    http://www.mississippivalleyjeepers.com

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    Quote Originally Posted by SavageSun4x4 View Post
    Age old question:

    Where you would like to fall is in the "black" zone.
    The "blue" zone is going to possibly affect your highway MPG and have you turning a few more RPMs than you may desire.

    The "yellow" zone may not give you enough highway RPMs but most likely give you better low-end grunt.

    You will want to factor in your engine's torque and horsepower band to get better use of this chart.

    Jeep 4.2/4.0 L I-6:
    Horsepower (net) 185 @ 4750 +/-
    Torque (net) 220 @ 4000 +/-

    Jeep 2.5 L I-4:
    Horsepower (net) 123 @ 5250 +/-
    Torque (net) 139 @ 3250 +/-




    rpm_chart-2.jpg


    What I would tell you is: If you are ABSOUETLY POSITIVE you will never go beyond a 33 in tire then the 4.10 ratio would be perfect. But go beyond that and in tire size and you will wish you had gone to a deeper ratio.

    So if you MIGHT go bigger, but not sure when or how big then I would go with 4.88's







    Useful; thank you.

  8. #8
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    Jeff, this is one of the few times I disagree slightly with Don. Unless I missed something, you are running 33" tires? What tires? What width? Are you running your original wheels? The reason I ask is that your Jeep has 3.73:1 and you were running 30"x9.50"x15" tires if they were the stock size. You would be okay with 4.10's but I am with Fred and wouldn't go any deeper than 4.56:1 gears. You live in Ohio, are you planning on moving to a mountain state anytime soon? I am in the process now of putting 4.56:1 gears and 33"x10.50"x15" BFG AT/KO's on factory rims in my '06 Unlimited with the 4.0L and automatic. My other Jeep is an '02 Wrangler with 4.0L and 5-speed and it now is running 4.88:1 and 35"x12.50"x15" on steel rims. I was running the same tires with 4.56:1 gears and my only issue was pulling long hills on the interstate here in Colorado I needed 4th gear. When I was up at Ft. Lewis, WA I had no issue pulling hills on I-5 or I-90 in 5th gear running 4.56:1 gears, but did struggle when I was running Interco Trxus MTs mounted on steel rims. The differance? Rolling resistance of the tread and the weight of the tire and wheel combination. Now I have added about 500 rpm to run at 75 mph on I-25 and lost about 1 mpg on my commute to and from Fort Carson, but the Jeep drives a lot better. I will be able to tell you how the '06 with the auto runs in about a week, but at this altitude, I am not getting the HP out of my 6cyls as you are, so I am will to give up a little mpg to gain some performance. I think you will find your Jeep running great, but you will be turning about 3,000 rpm to do 60 mph on the hwy.

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    http://www.grimmjeeper.com/gears.html
    Use the pulldowns to select the components you have and do a side by side comparison of 2 different ratios at the same time.
    http://zhvac.webs.com/

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  10. #10
    Senior Member SavageSun4x4's Avatar
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    Quote Originally Posted by FrankZ View Post
    http://www.grimmjeeper.com/gears.html
    Use the pulldowns to select the components you have and do a side by side comparison of 2 different ratios at the same time.
    Frank, does I checked and feel its not all telling. It does not factor in a SS...
    Don

    '15 Jeep Unlimited Rubicon Hard Rock...OLD SCHOOL 6 Spd Manual Trans
    17 Oaks Ranch Companies LLC

    www.savagesun4x4.com

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