6MT + 4.88 + 35s; anyone do it?

[HONCHO]

coming from an 03 Rubicon , i found the lack of low rpm torque for off road use unacceptable with the manual , 5:13 helped a bit but still nowhere as good as earlier editions . i dont know how people tow large weight with the manual. much less go off road . but my idea of off road might be different then the average new jeep owner .

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[Jt-wrx]

I spent a day driving a buds 03 rubicon and ya I love those 4.0 inline tractor engines. It was like driving a tractor in comparison to my truck. We took my truck the next day. Being two Jeep guys we wanted to see the difference, both days hunting. We barely went over 60 mph in his and not be too uncomfortable on highway, we were faster acceleration and zipping down highway at 80 mph in Cadillac by comparison.

And I towed near 3400 lbs of trailer with 380 lbs of people and 5100 lb Jeep no problem at all.

62 mph in 4th about 3000 rpm just staying under when second stage oil pump would come on. Gobs of power there and that’s what was needed for fighting the wind for hundreds of miles on way home. We were in 5th gear about 72 mph for those same hundreds of miles all they way up. And held cruise plenty fine on lots of the dips.

 

[piroman683]

Anyone go 4.56 and 35s yet? All the charts say that's the sweet spot for 35s

yup, it's awesome!

 

[piroman683]

I have a MT with 35's, and went from 3.73 to 4.56. This is a hell of a lot better both off road and on the highway. I should have done 4.88's to be honest as I'd have a little more pep in the desert, but I'm still happy with the 4.56

Here is my approach to this. I looked at what tire/gear ratio was used on the max tow (4.10 with 245/70/17's). Then I looked at what i have (315/70/17 with 3.73) so the new ratio to match max tow is 4.79. Well, no one makes 4.79 so the closest was 4.88 (.09 away) or 4.56 (.23 away). I opted for the 4.56 because it seemed like the best tradeoff for what I do which is 75% highway, 20% desert prerunning, and 5% trail crawling. How it would be better off roading with 4.88's but I can always swap later if I really need to. I have literally zero interest in going to larger tires.

 

[RodRecket]

I have a MT with 35's, and went from 3.73 to 4.56. This is a hell of a lot better both off road and on the highway. I should have done 4.88's to be honest as I'd have a little more pep in the desert, but I'm still happy with the 4.56

Here is my approach to this. I looked at what tire/gear ratio was used on the max tow (4.10 with 245/70/17's). Then I looked at what i have (315/70/17 with 3.73) so the new ratio to match max tow is 4.79. Well, no one makes 4.79 so the closest was 4.88 (.09 away) or 4.56 (.23 away). I opted for the 4.56 because it seemed like the best tradeoff for what I do which is 75% highway, 20% desert prerunning, and 5% trail crawling. How it would be better off roading with 4.88's but I can always swap later if I really need to. I have literally zero interest in going to larger tires.

Thanks for sharing. I also have no interest in going bigger than 35s (had two daily driver rigs on 37s and regretted it) and think 4.56 seems like a great highway, street, occasional offroad and tow middle ground. Good to hear someone with actual experience with that combo

 

[Dewyaw]

As I recall in 4th which is supposed to be the 1:1 towing gear, I was able to set cruise into the wind pulling my trailer at 102 km/h and it wouldn’t engage the second stage oil pump. That’s about 63 mph and right at 3000 rpm. And if I shifted into 5th it would lug and maintain 106-107 km/h but it felt too low in rpm and bogged. So I just went 4th and dropped speed until it wasn’t tripping in the second stage oil pump. So ya, not sure you’d want any worse than that.

Future Mojave owner here....what is this 2nd stage oil pump I’m reading about? What is that, will I have one, how do you know it comes on?

 

[Jt-wrx]

Future Mojave owner here....what is this 2nd stage oil pump I’m reading about? What is that, will I have one, how do you know it comes on?

lmao, in your information cluster where tire pressures and oil temperatures etc. is, one of the tabs is oil pressure, just put it on that tab while your driving and watch the two different oil pressures, one is like 28-30 psi for under 3000 rpm and then a bit over 3000 rpm the second stage comes on and from recollection it's 67-70 psi

so it's pretty easy to get your cruise control and gearing set up to be just under that while towing or cruising on the hwy

 

[Surfer Boy]

yup, it's awesome!

2021 Gladiator Rubicon Manual Trans. 35 12.50 17's Nitto Grapplers installed. Still 4.10. Should I regear to 4.56 or 4.88? Or leave it at 4.10?

 

[Jt-wrx]

2021 Gladiator Rubicon Manual Trans. 35 12.50 17's Nitto Grapplers installed. Still 4.10. Should I regear to 4.56 or 4.88? Or leave it at 4.10?

Did you not read the first two pages of this thread? Do that a couple times. 4.10 and auto transmission with 35’s be fine. Ideal for 35’s is 4.56, ideal for 37’s is 4.88, regardless of transmission but the automatic has a broader range.

Manual transmission gets a bit more specific.

My criteria was simple, I wanted to be a certain rpm on the highway in sixth gear at a certain speed.

Goal was 2500 rpm at 75 mph(120 km/h) so that I could cruise comfortably empty and still get decent mileage. 4.88, on 37’s. Goal achieved.

You also didn’t specify your usage goals. Towing? Crawling? Elevations you live at? All the information you could possibly want is in this thread.

 

[cgflyer]

ok so i run 4.88's with 6mt and 37's

68 mph in 6th is about 2250 rpm
75 mph in 6th is about 2500 rpm
80 mph in 6th is about 2700 rpm

2nd stage oil pump comes on at 3000 rpm, probably wanna stay under that for long periods of highway running

i live at 4000' elevation and routinely get up into the 7000' range when heading to mountains here, cruise control is so useable now, acceleration is fantastic, like stock or maybe a touch better (sport s with 3.73's was my base) and...

completely agree with the power at 2400-2500 rpm is fantastic for keeping things moving while not feeling like screaming, and it can hold most of the hills on cruise control on the hwy at those rpms, it really should be your typical max hwy cruise speed goal for running empty

i would personally not want to be any higher on the ratio than this to ensure i could get ok mileage on longer highway runs at 75 mph which is typical for my area

4.56 would be equiv to my set up for 35" tires

my rig tows great now too, i pull about 3800 lbs in total and if fighting winds i'll be in 4th but if not i'll be in 5th a lot more and just keep things under that 3000 rpm threshold when i can, mileage drops from 16 combined empty to about 11.9 straight highway when i tow my trailer full of week long camping stuff

see more here

note, i live in canada so i typically convert to u.s. figures, mileage/speeds etc. as the bulk of you JT owners are from well south of me, so the chart in the instagram is in km/h...the multiplier of mph to km/h is 1.609 so 100 mph is 160 km/h...you can math my figures a bit to see but 68 mph is 110 km/h, 75 mph is 120 km/h and 80 mph is 130 km/h essentially. my mileage is 14.7 l/100 km combined average over 7300 kms and towing mileage is 20 l/100 km...the u.s. translation is 16.0 mpg and 11.9 mpg

I'm on 35's and stock 4.10 and get 18-19 mpg consistently on highway, better without the RTT mounted...I've considered going 37's but not until I can afford the lift and gears (4.88 was my plan) but I don't think I can stomach 16 mpg.

 

[Jt-wrx]

gotta pay to play , i think you'll do better with the auto, likely 17 combined over time

 

[Bbannongmu]

6 Speed MT. Mickey Thompson Baja ATZP3 will be mounted Monday. Will drive on stock Rubi 4.10 gears for a while but will regear.

 

[Bbannongmu]

6 Speed MT. Mickey Thompson Baja ATZP3 will be mounted Monday. Will drive on stock Rubi 4.10 gears for a while but will regear.

Done. I’ll share some video on YouTube when I get a chance. https://www.youtube.com/c/JTRSpartacus #JTRSPARTACUS

 

[loudog3114]

Goal was 2500 rpm at 75 mph(120 km/h) so that I could cruise comfortably empty and still get decent mileage. 4.88, on 37’s. Goal achieved.

How about 80? 85? Pretty standard speeds where I live. When does the oil pressure kick in to high? I was thinking 5.13s but I don’t want to be long distance cruising at 75psi.

 

[Jt-wrx]

How about 80? 85? Pretty standard speeds where I live. When does the oil pressure kick in to high? I was thinking 5.13s but I don’t want to be long distance cruising at 75psi.

80 mph in 6th is about 2700 rpm. I didn’t check 85, but suspect it would still be about the limit before you’d push to stage two. Not sure what the diff is to 5.13 either. I’d guess you could 80 with 5.13 and not trip into stage two. But probably not much more with 37’s and a 6 speed manual.

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