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Discussion Starter · #1 ·
Hey everyone, I had some 4.56 gears installed into my Wrangler yeserday (4.0L 5 speed) and figured i'd give everyone some insight as to my findings -

On the drive there (about 220 miles) jeep had 3.73 gears, 30" tires, and we were doing between 66 and 68 mph pretty much the whole way (highway/interstate driving). We got 15.7 Miles to the gallon.

On the drive back, jeep had 4.56 gears, 30" tires, and we did 65 pretty much the entire way. On the way back we got 15.2 Miles to the gallon.

I'm actually suprised it didn't drop more, I figured it would have. With the 4.56s we were spinning just under 3000 rpms just to hit 65, i'm not sure I would want to rev it up much past that for long periods of time.. maybe 70 tops. Anyways, I just wanted to add a little bit of insight for everyone as people ask MPG questions fairly frequently. Hope everyone is having a great day!
 

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That your mpg didn't drop significantly after regearing from 3.73 to 4.56 isn't surprising. The rpms 4.56 produces with 33" tires puts the engine into its power band so it runs very efficiently there.

Thanks for confirming that often mentioned trait and letting us know.
 

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Discussion Starter · #3 ·
I would assume that the loss in MPGs when i actually add the 33" tires will probably be more than the .5 MPG loss that i saw from the regear, hope it isnt TOO much :) I'll let everyone know what that change is when I put bigger tires on.
 

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Pretty much the same result in mine when I went from 3.07's to 4.56's. From about 15.7 mpg to 15.3 or so. :wavey:
 

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I'm running the same setup that you started with, and have been wondering what going to 4.56's would do. This thread helps me a lot! Thanks for posting:thumb: Although I'm wondering since you wer'nt even at 3000rpm with 30's, mabee 4.88 might be better since I'm planning on going to 33's and mabee 35's in the future.
 

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Discussion Starter · #6 ·
Strongarm, I too pondered 4.88s slightly as I MAY get 35s instead of 33s, not totally sure yet.

I am glad that I didn't though, as 4.88s with 30s would be pretty crazy. I dont think you would be able to even go 65. I mean, you could do it but you arent going to drive any distance that way. the engine would be screaming. You wouldn't even have a use for 1st gear. I hardly do as it is. 2nd gear starts up a hill are no problem for me.

Additionally, just so you are aware, you would not be able to get a speedo gear that is calibrated for 4.88s and 30s. I needed a 43 tooth, and thats the biggest they make. If your planned setup would be for just a short length of time it wouldnt be a big deal, but if it would be for a while, just be aware that you would be racking up some "phantom miles" since you cannot even get a high enough toothcount gear.
 

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just be aware that you would be racking up some "phantom miles" since you cannot even get a high enough toothcount gear.
:rofl: my jeep has some of those :rofl:
 

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I would use GPS to caculate the speedo reading at say 65 MPH. Caculate the percentage difference and factor that into the miles driven then do your MPG caculation. Mine is 6.6% with 31.10.5x15's so I add 6.6% to my miles traveled between fillups and get 19 MPG highway.
 

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Discussion Starter · #9 ·
Yeah I get what you're saying about calculating mpg, that wouldn't be too hard. I guess I was more referring to potential resale value, or driving pas a parked cop and thinking... crap! What is 76% of 80 mph etc :)
 
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