Gear Ratio for 35's on 1999 TJ 4.0?

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ChrisTothC T

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Hey, so I'll be putting on 35's to my 1999 TJ with a 4" lift. Now I hear about re gearing so the car will run better, and so I'm confused with the chart about what I really need. So I was wondering what gear ratio I need for my build? I was told 4.0 by Extreme Terrain but I did the equation from some guy on youtube and got rounded to put in a 4.56.

I'm not sure so I appreciate every answer.

Thanks
 
I run 4.88’s with my 4.0/5spd(ax15) combo and 35’s. I sit around 2800rpm at 70mph. I think if I had to choose again I’d go with 4.56’s considering how much highway time mine sees. But the motor really doesn’t mind the RPM and anything over 70mph feels like you’re running with a sheet of plywood in a wind storm anyway lol
 
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Another vote for 4.88 or 5.13's I'm running 4.88's on 33's with a 4.0 and 5 speed and absolutely love this set up I'm turning 3000rpm at 75. We just got back from a road trip from upstate New York to texas and new mexico, most of the trip we were running 75-80mps with no problems
 
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Thanks for the replies guys, so it looks like 4.88 or 5.13 would be optimal, don't know why I was told 4.10 would be fine. What's the main difference between the 4.88 and 5.13? I just want to make sure I get the correct setup you know?
 
ChrisTothC T said:
Thanks for the replies guys, so it looks like 4.88 or 5.13 would be optimal, don't know why I was told 4.10 would be fine. What's the main difference between the 4.88 and 5.13? I just want to make sure I get the correct setup you know?
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About 100-150 RPM at freeway speeds... or maybe 100 RPM at city speeds. They’ll be very close. 5.13 will give you a small advantage in torque at all speeds, 4.88 might net a little bit of fuel economy at highway speeds. Other than that you won’t see much of a difference between the two.
 
ChrisTothC T said:
..., don't know why I was told 4.10 would be fine. ..
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Because the charts are only acurate for transmissions without an overdrive. Your's has an overdrive.

The difference between 4.88 and 5.13 is a small difference in rpm.

Mine is geared for 3k rpm at 75rpm. The Jeep has been all over the West and Midwest with that setup. I've been very happy with it, even on the highway traveling 75mph+ for long distances across flat Nebraska.
 
Steel City 06 said:
About 100-150 RPM at freeway speeds... or maybe 100 RPM at city speeds. They’ll be very close. 5.13 will give you a small advantage in torque at all speeds, 4.88 might net a little bit of fuel economy at highway speeds. Other than that you won’t see much of a difference between the two.
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Oh okay, so since 35's will make the Jeep lose power, the optimal choice would be 5.13, also I'm not on the highway that much so it'd make sense.
 
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I have a 97 with the 4.0 and AX-15. The PO put in 4.56 gears and while it's a little sluggish climbing hills at 75 mph, it's pretty good in all other areas from what I've experienced. I haven't been in a same setup Jeep with 4.88 or 5.13 gears though so I can't tell you one is better than the other. I think I run around 2500/2750 rpm at 75 mph.

My recommendation is try and find a off-road shop nearby and ask if they have any TJ's with this range of gearing you could check out.
 
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They put 4.10's in the 2.4/2.5 liter Jeeps. Also in 4.0 Rubicons with 31" tires. Going up to 35's I don't understand anyone recommending 4.10's. I think the Rubi is geared about perfectly, but only because of the extra low in 1st gear. I'm surprised the folks with a non-Rubi don't regear just running stock tires. If you aren't trying for max mpg's then I'd say go with the lower 5.13's. I think you'll appreciate it at every red light.
 
I vote for 5.13’s being too low for your needs and the area. But that’s just my opinion. Also, idk what type of wheeling you’ll be doing(if any 🤷🏻‍♂️). But I think if it isn’t going to be loaded down with gear/armor/bumpers that 5.13’s may be too much. Again, just my opinion.
 
According to grimmjeeper.com

AX15/34”/4.56=2670rpm @ 75mph
AX15/34”/4.88=2857rpm @ 75mph
AX15/34”/5.13=3004rpm @ 75mph
 
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I'm at 5:38 with an NV3550 manual on 35" KM2's , they are actually 34". I have no complaints. plenty of power.
rpm 3100 = 75 mph
rpm 2900 = 70 mph
rpm 2700 = 65 mph

edit: taken from the Grimmjeeper also
 
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