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Old August 3rd, 2011, 12:59 AM   #1
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Default Gearing help

I just went from 245/75/17 mtr's to 33/12.50/16 and my gas milage is hilarious. It's a 2000 jeep Cherokee with a stock power / drive train. If my stock gearing is 355, what would be the best upgrade is gears? My biggest concern is fuel efficiency, as this is currently my dd.
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Old August 3rd, 2011, 02:02 AM   #2
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3.73s for mpgs, 4.10s for a little bit of power and gas mileage then if you plan on going bigger somday 4.56s
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Old August 3rd, 2011, 02:06 AM   #3
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Yer 245/75's are 31.4 inches tall so you did not go up all that much in size with the 33's. Did you recalibrate your speedometer? Keep in mind that you are now driving faster than your speedo shows. That also means that your motor is working harder to make you go those speeds so if you calculate your mileage off the stock speedo reading it will be off. If you really wanted to switch gearing for a 2 inch tire size difference, go to 3.73's but I dont think its necessary unless you want to get some power back.

If your absolute biggest concern is MPG then put the 245's back on
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Old August 3rd, 2011, 02:18 PM   #4
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So is it worth while to do the 373 with out lockers? I'd rather upgrade gears at this point than down grade tires.
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Old August 3rd, 2011, 02:24 PM   #5
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I recommend going to 4.10s since you have a auto trans 3.73s wouldn't be much of a jump and you will wish you went lower in the future. You can add lockers at anytime but if you have a d35 id leave everything how it is until you can afford and new rear axle
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Old August 3rd, 2011, 02:38 PM   #6
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I have the Chrysler 8.25. And fwiw my mpg was pretty shitty before as well. So 410 is what I want? Any recommended shops near royal oak?
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Old August 3rd, 2011, 02:43 PM   #7
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Ok well then you can regear those axles and lock them as well at any point. I would go 4.10s. Idk of anywhere in royal oak but I'm sure someone on here could do it. I got my axles done at randys ring and pinion on walton in waterford
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Old August 3rd, 2011, 02:46 PM   #8
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tube bending and gear installs pm me for info! gears installed for $150 and up per axle.
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Old August 3rd, 2011, 02:53 PM   #9
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I would re-calibrate your speedometer and figure out what you actual mileage is first if your really that worried about it.
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Old August 3rd, 2011, 03:06 PM   #10
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and remember that any change to a numerically higher gear (373, 410, etc) will require a new carrier for the D30.

Like this, but you might find one used on GL4x4

http://completeoffroad.com/i-122971-...-d-706008.html
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Old August 3rd, 2011, 03:35 PM   #11
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Don't change anything, you're wasting your money. Going to 3.73's or 4.10's most likely will not increase your fuel mileage. You did not state if most of your DD driving is highway or city.

Do some simple math. How much did your mileage change? What is that increase in cost per week/month/year? How much will regearing cost? What is the difference? What have you gained? How long will it take to break even?
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Old August 3rd, 2011, 03:37 PM   #12
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Quote:
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x a lot
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Old August 3rd, 2011, 04:02 PM   #13
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What is your mileage/was your mileage?
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Old August 3rd, 2011, 04:21 PM   #14
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I agree with them any gear change probably isn't worth the change unless you want the extra power for wheeling and your mileage is suffering that much. Id wait for regear when you go to a 35 or bigger for costs purposes. Regearing will be more expensive then the lil extra u spend in gas
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Old August 3rd, 2011, 05:09 PM   #15
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Originally Posted by 2fst4you View Post
I agree with them any gear change probably isn't worth the change unless you want the extra power for wheeling and your mileage is suffering that much. Id wait for regear when you go to a 35 or bigger for costs purposes. Regearing will be more expensive then the lil extra u spend in gas
As many questions as you ask here, i dont think you should be giving advice. Im not being a dick, just saying. But suggesting a 3.55 to 3.73 gear swap is one of the dumbest things i have ever heard. Hell even to 4.10 really wont net much of a gain. It will be noticeable but im guessing any mileage increase would never pay for the gear swap in the long run. What is hurting the OPs mileage is the heavier tires AND the rolling resistance. Xjs dont get real good mileage to begin with so im not sure what he is calling bad. If the OP is getting 15-16 mpg I think he is doing good. Again im not being a dick. Im just saying.
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Old August 4th, 2011, 06:27 AM   #16
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As many questions as you ask here, i dont think you should be giving advice. Im not being a dick, just saying. But suggesting a 3.55 to 3.73 gear swap is one of the dumbest things i have ever heard. Hell even to 4.10 really wont net much of a gain. It will be noticeable but im guessing any mileage increase would never pay for the gear swap in the long run. What is hurting the OPs mileage is the heavier tires AND the rolling resistance. Xjs dont get real good mileage to begin with so im not sure what he is calling bad. If the OP is getting 15-16 mpg I think he is doing good. Again im not being a dick. Im just saying.
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Old August 4th, 2011, 01:18 PM   #17
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Well it's mostly city driving. Although I went to clarkston the other day, a round trip of about 45 miles and I burned a half tank. I was getting about 9-12 mpg city before, now I figured 6-8 mpg. I haven't done much to the power train other than a triple core aluminum radiator and a 185* thermostat. I'm not expecting 30 mpg, but anything I can improve with out down grading is what I want to do. I just did wheel bearings, axle joints, ball joints, brakes, rotors, calipers, coils springs, adj track bar, and a drop pitman arm. I just want some mpgs back if possible, and some power.
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Old August 4th, 2011, 01:30 PM   #18
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Seems pretty rough, mine with 3" lift and 31's got about 16 mixed driving and dads with 6.5" and 32's gets 14. Both have/had 3.55 gears.
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Old August 4th, 2011, 01:31 PM   #19
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A 4.56 is about your best bet. But i doubt you will see over 12 mpg. Fix your speedo so you can get a accurate reading and then do gears.
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Old August 4th, 2011, 01:33 PM   #20
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Gearing isn't causing that shitty mileage. When's the last time you did a tune up, o2 sensors, etc?
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