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I am planning on lifting my 2017 JKU with a metal cloak lift (3.5in) and also adding either duratrtacs or Ko2 35in tires.... this jeep in the only vehicle I own making it my DD... looking to regear once the lift and tires are on to get better distribution of power but unsure if I should run 4.56 or 4.88 gears

Mostly highway traveling in Northern VA area/ Washington DC, about 12 times a year I take it on trails


looking for any advice for someone running a similar setup

thanks in advance.
 

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There is the regearing chart I recommend 4.56 at 2600-2800 RPMS I'm at 72-77 mph perfect for keeping up with traffic and passing. With 4.88 at 75MPH you will be around 3200 RPMS maybe a little less but surely close or above 3000RPMS at 75mph something I do not recommend....can the Jeep handle it? Sure...keep in mind the fuel also with 4.88 you will be spending more.
 

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4.56

I am getting these gears installed now for my KO2 37's only because I intend to get a turbo installed at some point. 4.56 is Perfect gearing for KO2 35's.
 

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4.88. And I wished I went 5.13. 315 duratracs are only 33.75" inches tall with weight on them, so use 34" in that chart above. The 3.6 loves to rev, and running 2800 rpm at 70mph actually helped my mpg over the factory 4.10's.

If you want a good gear installer who's half the price of the shops in northern VA, PM me.
 

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4.88 will not run 3200 at 75. I run the equivalent (5.13 with 37s) and nowhere close to 3200, probably don't even break 2800 at 75. For the JK 3.6, it likes these higher RPMs and runs more efficiently. It's not like older engines where high RPMs were bad.

Either 4.56 or 4.88. I would personally do 4.88. It's not super deep and gives you real power. It is also helpful Offroad.

Gear charts go by advertised size - not actual mounted size. But either way, round up or round down, the difference will not be that significant.

I don't think I would do 5.13 with 35s - that will be a little deep. Not as pavement friendly, but would really crawl offroad. 5.13 is perfect for 37s - good street manners, a beast Offroad.
 

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Gear charts go by advertised size - not actual mounted size.
Actually, if you do the math, the commonly posted chart uses the size column (e.g. 35) as the weighted rolling diameter, so it is quite misleading. To be useful, one has to interpolate using 33.7 for the average 35, or 33.5 for a small one.

This is one of reasons I wrote my own calculator. The other is that I wanted something would cover any speed in any gear, and for all four engine/transmission combinations possible on a JK(U).

Mark

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The chart is only useful for determining RPM at speed; ignore the colors. You're in my area, and 4.56 will be just fine, with 4.88 being overkill.
 

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4.56 should have been the factory standard alone with BFG KO2 in 35's

2100 rpm at 55mph
2300 rpm at 60mph
2500 rpm at 65mph
2700 rpm at 70mph
2900 rpm at 75mph
3100 rpm at 80mph

Add about 150rpm more to this if you go with 4.88's

All values using the A5 trans, 4.56 and 315/70/17 KO2's.
 

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The KO2s run small. Had I did enough research to know this ahead of time, I would have leaned more towards 37" KO2s knowing that when I re-geared, I'd be more in line with the chart.

Go 4.56 is you're on the highway, 4.88 would be too steep and driving 75 to 80 MPH on a freeway is a little unsettling for prolonged periods of one.

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