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Old 06-25-2009, 12:31 AM   #1 (permalink)
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Mpg

Does anyone know what mpg difference to expect between running standard gearing with 33" tires and 4.88 pinions with 33" tires?

Also what mpg difference would you expect to lose going from 4.88 with 33" tires to 35" tires?
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Old 06-25-2009, 03:57 AM   #2 (permalink)
 
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well first off do you have an auto or std. and what gearing do you have now? I have and auto that had 3.07 stock and went to 4.88 with 33's. Badass crawling but horrible on the highway. 35's will help but 4.88 are pretty low.
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Old 06-25-2009, 04:40 AM   #3 (permalink)
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Sorry forgot to mention, its a manual with standard ratio, not 100% sure what ratio that is though! lol 3.73??
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Old 06-25-2009, 05:16 AM   #4 (permalink)
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I have an 02 4.0L, 5spd, 4.88s and 35s and get about 14.5 mpg.
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Old 06-25-2009, 06:43 AM   #5 (permalink)
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Sorry forgot to mention, its a manual with standard ratio, not 100% sure what ratio that is though! lol 3.73??
That still doesn't really tell us much. What year Jeep and what manual trans ??????
You do know that different transmissions have different top gear ratios.
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Old 06-25-2009, 07:41 AM   #6 (permalink)
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Wind resistance will affect it more then tire size, the more you lift, the less you get because there's even more brick wall in the breeze. What lift you have?
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Old 06-25-2009, 07:55 AM   #7 (permalink)
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Your MPG will go down with larger tires, more lift, more weight, more power.
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Old 06-25-2009, 08:37 AM   #8 (permalink)
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I don't want to sound like a butt,,,,,,,, However, if MPG is a major issue, leave the Jeep as is. I have a 98 TJ, 4.0L, 4:56 gear, 33 inch tires, AX-15 tranny, bumpers, tire swing, winch, skids, etc., etc., I get about 11 MPG as is (don't use AC)...... a newer Jeep will probably do better, but if the loss of 4 or 5 MPG is an issue, don't do the mods.

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Old 06-25-2009, 09:06 AM   #9 (permalink)
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Probably didnt explain my reason for asking very well, I am running standard ratio in the axles Dana 44 and 30 (I think 3.73 ratio) with the standard gearbox etc it is a 1999 Wrangler Sport 4.0L

Mods are 33in tires, 6in lift.

Reason i asked is I am going to build up the axles with cromo shafts, lockers and 4.88 pinions and would expect to probably gain some MPG over running the Jeep hard on standard ratio and big tires!
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Old 06-25-2009, 09:16 AM   #10 (permalink)
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Probably didnt explain my reason for asking very well, I am running standard ratio in the axles Dana 44 and 30 (I think 3.73 ratio) with the standard gearbox etc it is a 1999 Wrangler Sport 4.0L

Mods are 33in tires, 6in lift.

Reason i asked is I am going to build up the axles with cromo shafts, lockers and 4.88 pinions and would expect to probably gain some MPG over running the Jeep hard on standard ratio and big tires!
6 inch lift for 33's?

I went from 3:07 gears to 4:46 ratio. Swapped in a Ford 8.8 axle with Detroit locker & Yukon shafts. D30 basically stock other than gears & Aussie locker. I gained lots of low end torque, a real sweet crawl, tractor like power when in 4lo, and the use of 5th gear on the Hwy.,. However, I cannot say that I gained any MPG. I might have and just don't know it. I know that I have lost 4-5 MPG since being stock. Did I lose MPG because of gears, or because of heavy bumpers, winch, etc., etc.,? I don't know.
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Old 06-25-2009, 11:17 AM   #11 (permalink)
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Yea the lift is there for bigger tires, just put 33's on to make do while I get the axles done, 35's would of killed my highway speed and crawling.
I think you have made a point with the added weight etc probably negates any MPG savings ahh well, the Jeeps are worth it
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Old 06-25-2009, 11:29 AM   #12 (permalink)
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i have a 88 2.5 5 speed i got 17 on the freeway this weekend 34 ltbs and 4.88 gears
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Old 06-25-2009, 11:35 AM   #13 (permalink)
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Yea the lift is there for bigger tires, just put 33's on to make do while I get the axles done, 35's would of killed my highway speed and crawling.
I think you have made a point with the added weight etc probably negates any MPG savings ahh well, the Jeeps are worth it
Keep in mind that going to larger tires with stock gears may have improved your MPG slightly while killing your power and causing the loss of 5th gear. The loss of 5th gear in city driving isn't an issue since you seldom use 5th gear in town. However, on a long highway trip, driving in 4th may have caused you to lose a few MPG. Of course, going to larger tires also screwed up your speedometer and odometer so they are off by 10% or so currently. Personally, I don't think any of this is worth the effort or thought to figure out. I will tell you the changing the gear ratio was the best mod that I have ever done, and if I had it to do over, I would have gone with 4:88 gears versus the 4:56.
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Old 06-25-2009, 11:42 AM   #14 (permalink)
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Cheers guys, need to keep saving and get the swap done then! lol

Little Jeep, are you on 35's?
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Old 06-25-2009, 11:47 AM   #15 (permalink)
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Cheers guys, need to keep saving and get the swap done then! lol

Little Jeep, are you on 35's?
No 35's here,,,, but they are in my future.
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Old 06-25-2009, 12:08 PM   #16 (permalink)
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haha your future holds the same as mie then! Cant wait!

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Old 06-25-2009, 01:19 PM   #17 (permalink)
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highjack

anyone with a 3 speed auto want to chime in and give your opinion for 4.56 or 4.88?

this is my new dilemma.
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Old 06-25-2009, 02:46 PM   #18 (permalink)
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anyone with a 3 speed auto want to chime in and give your opinion for 4.56 or 4.88?

this is my new dilemma.
From my understanding is if gear charts say 4:56 it is talking about a manual tranny. Autos need to go one deeper. So I guess if in doubt, go 4:88
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Old 06-25-2009, 03:38 PM   #19 (permalink)
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My friend has a TJ, 2.5 L 3 speed auto 4.88's and 35" KM2's.

He went from the stock 4.11's to 4.88 and at first he said it didn't seem to be a huge difference but his works well for a 4 banger. On the highway it screams around 3K. Still gets decent mileage.

Myself, I have a 4.0 AW4, 4.11's and 39.5" ( yeah it sux for crawling) just ordered 5.38's to make use of that 4th gear
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Old 06-25-2009, 03:53 PM   #20 (permalink)
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If its MPG your worried about,

Lose some of the lift, Like stated the higher lift is hurting your mileage.

I am running 35s on a 3 inch lift with now issues.

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Old 06-26-2009, 12:13 AM   #21 (permalink)
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If the Jeep is lifted high, how does this affect your milage, the gap is greater under the vehicle, so I dont see how the vehicle becomes less aerodynamic?

Not meaning to sound funny, just dont understand
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Old 06-26-2009, 04:00 AM   #22 (permalink)
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If the Jeep is lifted high, how does this affect your milage, the gap is greater under the vehicle, so I dont see how the vehicle becomes less aerodynamic?

Not meaning to sound funny, just dont understand
Kinda like a kite effect, The higher the big square box like body is in the air, the more the wind slows you down.

The air under the jeep does not help.
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Old 06-26-2009, 04:18 AM   #23 (permalink)
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Cheers Mike
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Old 06-26-2009, 03:22 PM   #24 (permalink)
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anyone with a 3 speed auto want to chime in and give your opinion for 4.56 or 4.88?

this is my new dilemma.
4.0L with the 32RH, 456's work very well...
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Old 06-26-2009, 08:15 PM   #25 (permalink)
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4.0L with the 32RH, 456's work very well...
but would 4.88s work better?
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