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Thread: Another gear ratio question

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    Default Another gear ratio question

    So rear end blew up and lookin at a rebuild..wonderin what gear ratio i should go with..i dont offroad too often and theres no rock crawling..im looking for a gear ratio that will let me get to 70mph on the highway and not get 10mph with 33s.. ive been told i could do it with 3.07s but ive read every where else that 3.07 wont do it..its a daily driver that will have a trip of 1k+miles of highway later this year..i had 3.73 and got 10mph at 70..and barely got to 70 any advice would be awesome, thanks

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    Land Squid Jeffb_79's Avatar
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    What engine are you running?
    4.10s with the I6 and manual trans should bring you back to a stock feeling/gas mileage.

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    Ive got a 97 wrangler sport so im running the I6 4.0 with 5spd manual trans and 33X12.50s the shop i have it as says 3.07 would be fine on the highway..i saw a chart that said 3.73-3.91 was ideal for gas mileage but 4.11 would get me closer to stock.. on the other hand ive read that 3.07 with 33s wont get up to 70..any truth?

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    No Balls muddyluxury's Avatar
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    http://www.grimmjeeper.com/gears.html

    this will allow side by side comparission of gears. I use stock gears and tires as my base line then figure out tire and gear combos from there.

    FWIW, to run 315 75 r16 roughly a 34 11.50 with a V8 and the 545rfe auto it says i need 4.56 for factory rpm range. and my own calculations in percent change for factory gears and tires to the tires i want and gears i want give me very similar numbers. just not a gear ratio that i can buy.
    -Jeb

    99 GC Ltd. V8. plenty of goodies, 6in lift 33s, rear locker, 12v cooler, steel bumpers fr+rr, Roof Top Tent,
    01 TJ 4.0 auto.. stock street queen for now.

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    Land Squid Jeffb_79's Avatar
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    Quote Originally Posted by Sniperx9119 View Post
    Ive got a 97 wrangler sport so im running the I6 4.0 with 5spd manual trans and 33X12.50s the shop i have it as says 3.07 would be fine on the highway..i saw a chart that said 3.73-3.91 was ideal for gas mileage but 4.11 would get me closer to stock.. on the other hand ive read that 3.07 with 33s wont get up to 70..any truth?
    I ran 3.07s with my last wrangler (I6 with 5 spd manual). It sucked. I never used 5th gear. Going around town I never got over 3rd gear. On the highway I'd get up to 4th gear, but would have to down shift if there was a hill.
    I'd go with 4.10.

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    The real question is, could you get up to 70-75 with the 3.07? and wouldnt my MPG go down with 4.10s?

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    No Balls muddyluxury's Avatar
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    Quote Originally Posted by Sniperx9119 View Post
    The real question is, could you get up to 70-75 with the 3.07? and wouldnt my MPG go down with 4.10s?
    the times you can spin a tire with fewer revs on the engine the better you mpgs will be. too a point, that point is when you have to run out 3rd gear to maintain speed a long shallow grade.

    run your numbers and compare them. i am sure you will want to be in the 3.91 to 4.11 range.

    correct me if i am wrong here, the other thing you need if you gear about 3.55 say 3.73 is a new carrier b/c of a size difference of the ring gear. I know in GCs it must be done to alot of the 4.0 base models with the 3.55 gears when they jump to say 4.10. but for anybody that had higher than 3.55 gears you can go as high as your pocket book can afford to put gas in.
    -Jeb

    99 GC Ltd. V8. plenty of goodies, 6in lift 33s, rear locker, 12v cooler, steel bumpers fr+rr, Roof Top Tent,
    01 TJ 4.0 auto.. stock street queen for now.

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    Land Squid Jeffb_79's Avatar
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    Quote Originally Posted by Sniperx9119 View Post
    The real question is, could you get up to 70-75 with the 3.07? and wouldnt my MPG go down with 4.10s?
    My mpg's went down when I went up in tire size... I can only imagine they'd go back to around normal when you set the gearing properly. Your trans/transfer case will like you much more with the proper gearing as well.
    I don't think I ever saw 75.... 70 maybe, on a downhill, with the wind to my back, and a fat guy in the passenger seat.

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    you will never get good gas mileage with 33's going 70 in a wrangler, it's that simple. that being said, if you want the rpms you would be at going 70 mph with 33's, then you want 4.10 gears.

    if you had more power than you would have a higher top speed with 3.07 gears, but since you probably have a stock 4.0, you'd never be able to reach that(not even close).

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    I ran 3.07's for a short while on 33's and it sucked ASS! Don't even consider it. The only way you're going to reach 70 mph like that is if you're going down hilll with a strong tail wind. I stepped up to 4.56's from the 3.07's and it was wound a little tight but was SOOOO much better than the 3.07's. 4.10's are probably your best bet.
    A proud member of the best "Most F'd Up Club" in SoCal: http://www.4x4corps.com/

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