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  1. #16
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    Mar 2009
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    Default Re: Tire Size and Gear Ratio

    Quote Originally Posted by Weldmen View Post
    I believe automatics are 3 speeds and the 4th would be OD.
    Hmmm my post is just way off. So is my RPM, I get 3000 rpm at 80 mph and I have 32" tires and 4.56 gears.

  2. #17
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    michigan
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    Default Re: Tire Size and Gear Ratio

    take ur rpm and times it by ur overdrive is what u guys are looking for
    example 31in tires and 3.55 gears = 2500 ish rpm times by .75 = 1800 ish rpms in overdrive. hopes this helps u guys
    Last edited by jeepxj95; 06-05-2011 at 01:23 AM.

  3. #18
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    Oct 2010
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    Coquitlam, B.C.
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    Default Re: Tire Size and Gear Ratio

    Dam those #`s are high. I have an automatic 96 XJ with stock 225 75R15 tires only mod I have done is Highflow cat & muffler to increased MPG (save gas) as it shifts into OD sooner.
    @ 71 KMPH I`m at 1250 RPMS and at 80 KMPH it`s 1500 RPMS. After these readings I hacked the front off of my air intake box and found it made a noticable difference in the smoothness of my engine and gear changing but nothing noticable on the rpm scale. Not sure if it`s good for everyone`s trails but works great for a DD.

    I`m still on the wire about the gears, I have heard people running 35`s with stock gears and no problems so Maybe it`s what kind of abuse you are going to put your gears & tranny through that really matters?

    Stock 3.55 gears, HWY 31`s trail 35`s ????????

  4. #19
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    Sep 2009
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    Chico, CA
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    Default Re: Tire Size and Gear Ratio

    Run 35s on stock gears? Possible yes, but advisable no. It would work well in a dedicated mud rig, but not otherwise advisable, particularly for highway use.
    230 hp 4.3L Chevy
    Built 4L60E with manual lockout
    Atlas 4 speed
    Griffin radiator
    On board air
    Warn 9.5ti on custom bumper
    7.5" RE front and bastard pack rear on custom long arms
    30 gal gas tank
    lockers
    And a bunch of other stuff

  5. #20
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    Aug 2009
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    Asheville, NC
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    Default Re: Tire Size and Gear Ratio

    I don't think I'd go 35's on the stock gears.. I think I'll stick with my 33's on the stock gears until I can afford to pick up some gears as well as a locker to install at the same time..
    FORMER GREEN XJ CLUB MEMBER
    IF YOU DON'T STAND BEHIND OUR TROOPS, FEEL FREE TO STAND IN FRONT OF THEM!!
    DOING SOMETHING JUST BECAUSE YOUR BUDDY DOES IT THAT WAY MAKES AS MUCH SENSE AS SHARING TOOTHBRUSHES

  6. #21
    Join Date
    May 2010
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    New Caney, TX
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    Default Re: Tire Size and Gear Ratio

    I am planning on running 35's on my stock gears for a while. However mine is mostly a trail rig, and I know it will never come out of 4lo with those tires on it. Not that it does with the 33's

  7. #22
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    May 2012
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    East TX
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    Default Re: Tire Size and Gear Ratio

    FYI,,,,, 410s with 33s put me 200 rpms at 55mph higher than stock 355 and stock tires,,,,,,,,,,in other words it corrected the speedometer within 2mph ,,, giving me 200 more rpms for loss of torque,,,,,456 would have made about a 500rpm differance ,,,,
    Last edited by Mudderoy; 06-20-2012 at 02:10 PM.
    2000 Sport 6.5 RC short arm w/ drop brackets,, settin on 33x12.5 ,,,,4.10's Detroit Trurax rear,Detroit Eloc infront

  8. #23
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    Default Re: Tire Size and Gear Ratio

    Quote Originally Posted by willtodo View Post
    FYI,,,,, 410s with 33s put me 200 rpms at 55mph higher than stock 355 and stock tires,,,,,,,,,,in other words it corrected the speedometer within 2mph ,,, giving me 200 more rpms for loss of torque,,,,,456 would have made about a 500rpm differance ,,,,
    Corrected the speedometer? There maybe a gear/tire combo that matches the 3.55/27 inch tire but to get the speedo right I think you really should change out the speedo gear in the transfer case. I guess some people don't really care, but I like having the speed right, for mpg calculations, and every time I see a cop.

  9. #24
    Join Date
    Oct 2012
    Location
    Sussex, NJ
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    Support Re: Tire Size and Gear Ratio

    This link is very helpful for selecting different tire diameters, gear ratios, speeds and rpm with different tire size and gear ratio combinations.
    http://www.novak-adapt.com/knowledge/gearing.htm
    Later............
    Dave

    Not sure if I can make it over the rock behind me but I'll give it a try.
    "Don't worry about nothin' 'cause nuthin's going to be Alright"

  10. #25
    Join Date
    Feb 2013
    Location
    W. Michigan
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    Default Re: Tire Size and Gear Ratio

    I have a 2000 XJ bone stock. I want to upgrade to a locker, but haven't decided which brand or which axle yet. How do I know what gear ratio I have? I under stand some came with LS in the rear, but my 8.25 chrys is open. How do I find the gear ratios for both front and rear?

  11. #26
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    Sep 2009
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    Chico, CA
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    Default Re: Tire Size and Gear Ratio

    Here ya go. This is for a front, but the back will be the same
    230 hp 4.3L Chevy
    Built 4L60E with manual lockout
    Atlas 4 speed
    Griffin radiator
    On board air
    Warn 9.5ti on custom bumper
    7.5" RE front and bastard pack rear on custom long arms
    30 gal gas tank
    lockers
    And a bunch of other stuff

  12. #27
    Join Date
    Oct 2011
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    S.E. Texas
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    Default Re: Tire Size and Gear Ratio

    Quote Originally Posted by 4.3LXJ View Post
    Here ya go. This is for a front, but the back will be the same
    Nothings showing up Steve.

    But there should be a tag under one of the bolts on either the front or rear diffs noting the ratio.

  13. #28
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    Sep 2009
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    Chico, CA
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    Default Re: Tire Size and Gear Ratio

    230 hp 4.3L Chevy
    Built 4L60E with manual lockout
    Atlas 4 speed
    Griffin radiator
    On board air
    Warn 9.5ti on custom bumper
    7.5" RE front and bastard pack rear on custom long arms
    30 gal gas tank
    lockers
    And a bunch of other stuff

  14. #29
    Join Date
    Feb 2013
    Location
    Hatteras Island NC
    Posts
    62
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    0

    Default Re: Tire Size and Gear Ratio

    I run in very deep, soft, and rutted sand. Large amounts of torque are needed.
    31" tires is where re-gearing begins. Otherwise you will need to run 4-low.
    3.55 and 31"s is fine for mallcrawling but not the desert.

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