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2000 xj aw4 on 34s 4.88 or 5.13

will i still hit 65 at 2600 rpm even after i messured my tires at 32-1/2
they say there 34s but the tape messure says otherwise
 
honestly 5.13 do sound pretty tempting our speed limits for were i go jeeping aren't higher then 90kms so hitting 100kms is a rare endevor lol

http://www.grimmjeeper.com/gears.html
just tried that link at 65mph im looking at 2654rpm
at 55mph id be at around 2246rpm
doesn't seem that bad and its not my dd its basically an exploration/ fishing and hunting rig
 
Andre2000 said:
What tcase did you drop in ?
Click to expand...

I'm running a NP231 with a Teraflex 4:1 kit (5 gear planetary), wide chain mod, and a Teraflex 2lo kit.
 
You are right in between 4.56 and 4.88. I think 4.56 is perfect for 33s and 4.88 is good for 35s. I currently have 35s with 4.56 and it feels a little sluggish. Either choice would work fine, just depends on your preferences. What is more important to you...peppy acceleration or fuel economy?
 
Andre2000 said:
honestly 5.13 do sound pretty tempting our speed limits for were i go jeeping aren't higher then 90kms so hitting 100kms is a rare endevor lol

http://www.grimmjeeper.com/gears.html
just tried that link at 65mph im looking at 2654rpm
at 55mph id be at around 2246rpm
doesn't seem that bad and its not my dd its basically an exploration/ fishing and hunting rig
Click to expand...

With those speed limits, I'd do 5.13 if its hilly.
 
Ol Blue said:
You are right in between 4.56 and 4.88. I think 4.56 is perfect for 33s and 4.88 is good for 35s. I currently have 35s with 4.56 and it feels a little sluggish. Either choice would work fine, just depends on your preferences. What is more important to you...peppy acceleration or fuel economy?
Click to expand...

what are you rpms like ?
 
Andre2000 said:
what are you rpms like ?
Click to expand...

I know you asked Ol Blue, but I'll comment that I'm running 31s and 3.55 gears, and I mostly drive around town and on the highway with the AW4 set to 3rd gear. This will allow the TC to lock in 3rd gear. The motor is doing 2700 rpm at 65 mph on the highway, and it feels great.

With that said, it took a while to convince myself to do this because it intuitively feels more natural to cruise a 6-cyl 4L motor at ~2000 rpm. But the 4L is dog below 2400 rpm, at least for highway cruising. Once it became obvious that highway driving at 2000-2200 rpm was out of the question, started thinking that I would aim for diff gears to turn 2500 rpm at 65 mph. However, other NAXJA members encouraged 2700+ rpm for the highway which corresponds to driving around with the AW4 set to 3rd gear for my setup, so I started doing that, and its been great. In fact, I'm fine with spinning the motor at 3000 rpm to go 73 mph which is my usual speed for 65 mph zones. :)
 
Don't overlook many of the real world variables that gearing calculators don't factor in:

Added wind resistance by lifting vehicle/roof rack/overhead cargo
Added rolling resistance of larger tires/increased contact patch
Added weight of non-stock bumpers, sliders, skids, armor, unibody plating, cargo, winch
Elevation and terrain where you commonly operate your rig. The engine will make more power below 3000ft than above 6000ft.
Peak power range of the 4.0L engine

Over the past 25 years, I've run XJ's with both 4:56's and 4:88's in rigs with 5-6" of lift and measured 33" tall tires, at elevations from 4000 to 10,000ft but most driving in the 4-5000ft range.

4:56's left the rig feeling underpowered and when cruising the AW4 would hunt between 3-4th gear at the slightest elevation change (overpasses, headwinds, etc) which builds heat in the transmission and burns extra fuel.

4:88's have been the perfect fit and I've run this gearing/tire combo since 2007. RPMs at 65mph are in the range you are looking for and the transmission is happy. Low end power is great and in 16 years, I've never once wished for taller gears. I often have the cruise control set at 75mph turning about 2850rpm and the 236k mile 4.0L hums along just fine, averaging 15mpg freeway at that rpm.
 
Last edited:
Andre, I'll get you a real world number tonight. The calcs put me around 2200 RPM @65mph but I feel like that is way lower than my actual, likely due to added weight and decreased aerodynamics. It should be noted that these gear ratio calcs don't account for any friction losses so the RPM they spit out is the theoretical best case number. Like if you ran the Jeep up to 65mph on jackstands.

Great point about the elevation XJEEPER, didn't even think about the engine having to work harder at elevation.
 
The altitude really isn't much of a issue, I've spent a lot of time running above 10000 with only a slight power loss.
 
If you assume 3% power loss per 1,000' above seal level, that adds up to a 30% power loss at 10,000'. I'd call that significant. For those of us around Denver that's about a 15% power loss which certainly is not insignificant.
 
Andre2000, at 65mph I'm at about 2400 rpm. Kinda hard to tell exactly but it's between the 2250 and 2500 lines and closer to 2500. Measured my 35s at 33.9" under vehicle weight.
 
awsome info guys !
i called interco about my tires and they told me to remove one from the jeep lay it down and inflate it to max pressure then messure accross and i got 3.6 wich is the spec they gave as well
so im pretty close to that 3.9
 
XJEEPER said:
Don't overlook many of the real world variables that gearing calculators don't factor in:

Added wind resistance by lifting vehicle/roof rack/overhead cargo
Added rolling resistance of larger tires/increased contact patch
Added weight of non-stock bumpers, sliders, skids, armor, unibody plating, cargo, winch
Elevation and terrain where you commonly operate your rig. The engine will make more power below 3000ft than above 6000ft.
Peak power range of the 4.0L engine

Over the past 25 years, I've run XJ's with both 4:56's and 4:88's in rigs with 5-6" of lift and measured 33" tall tires, at elevations from 4000 to 10,000ft but most driving in the 4-5000ft range.

4:56's left the rig feeling underpowered and when cruising the AW4 would hunt between 3-4th gear at the slightest elevation change (overpasses, headwinds, etc) which builds heat in the transmission and burns extra fuel.

4:88's have been the perfect fit and I've run this gearing/tire combo since 2007. RPMs at 65mph are in the range you are looking for and the transmission is happy. Low end power is great and in 16 years, I've never once wished for taller gears. I often have the cruise control set at 75mph turning about 2850rpm and the 236k mile 4.0L hums along just fine, averaging 15mpg freeway at that rpm.
Click to expand...




75 mph sounds pretty nice at that rpm my tires are pretty close too, does it ever hunt with the 488s ?
 
Been using that calculator a lot think I’m going to order 5.13s
Seeing as it’s only a Bush truck and only like 150-200 rpm difference from 4.88
 
Andre2000 said:
Been using that calculator a lot think I’m going to order 5.13s
Seeing as it’s only a Bush truck and only like 150-200 rpm difference from 4.88
Click to expand...

With your tire size, 5.13 is 55 mph at 2200 rpm which is the lower threshold for useful TQ levels. 2400 rpm is 60 mph where there is plenty of TQ. 65 mph is 2600 rpm which is perfectly comfortable for the motor. 75 mph is 3000 rpm which is on the verge of buzzy for long distances, but will you ever drive for any distance at 75 mph?
 
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