4:88s, not so popular, but gonna try it

wayoflife

Administrator
Staff member
We are running 5.13 & 37" Cooper's. Around town there is lots of hills, it never see's 8th. Mainly 1-6. Oh the highway it down shifts awfully early from 8 to 7 on the slightest grade.

If a person wants see 8th even on slightest grade you would go 5.38.

Just to make sure, you did recalibrate your speedometer, right? Because, I'm running 37's on 4.10's and see the same thing, 1-6.
 

13_gecko_rubi

New member
I should also note that of the JL's I've seen running 5.38's and 40" tires, none have seemed to perform that great. I don't know if it's a shift point issue or what but for instance, Tom from PSC was having a hell of a time keeping up, even on the highway when climbing grades. I could literally hear his JL bogging down and then hunt for gears all the time. Granted, he was running heavier axles and pushing 40's but I would have thought the 5.38's would have more than made up for the difference. It was almost as if he were running an old JK with a 3.8L - ask me how I know. :rolleyes2:
Lol. A good ole 3.8 comparison SMH.

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wayoflife

Administrator
Staff member
Lol. A good ole 3.8 comparison SMH.

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LOL - For the better part of Moby's life, that's what he running. A 3.8L with a 6-speed and pushing 40x15.50's. :crazyeyes:

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All I'm saying is that in spite of what Tom was running, he was still having issues keeping up and in a similar way to what I remember on Moby back in the day.
 

13_gecko_rubi

New member
LOL - For the better part of Moby's life, that's what he running. A 3.8L with a 6-speed and pushing 40x15.50's. :crazyeyes:

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All I'm saying is that in spite of what Tom was running, he was still having issues keeping up and in a similar way to what I remember on Moby back in the day.
Ya I talked to him and Loren about the issues they were having. Weird

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wwood

New member
We are running 5.13 & 37" Cooper's. Around town there is lots of hills, it never see's 8th. Mainly 1-6. Oh the highway it down shifts awfully early from 8 to 7 on the slightest grade.

If a person wants see 8th even on slightest grade you would go 5.38.

Just curious. We have Cooper 37's on our JLUR with the 8 speed auto trans and factory 4.10 gears and can see no need to run lower gears even in our hilly area for daily driving. Our Jeep runs in 8th on flat roads and mostly 7th on mild grades, it does go into 6th on significant grades. But my question is so what? Why is it a problem to run in 7th or 6th on uphill grades? As long as the tach is at a reasonable RPM (around 2,000-2,500) I don't see any issue. Plus if the Jeep picks 7th on a grade that the Jeep will actually pull without lugging in 8th gear you can simply shift to manual and put it in 8th gear. :)
 

wwood

New member
Yes, mainly higher rpm's on the street & too slow of a 1st gear crawl speed on trail.

A built LS2 would help lots too.


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I think you guys are missing my question. I understand that when you put bigger tires on the factory gears that you raise the overall gear ratio which lowers RPMs on the highway, which means you probably can't pull high gear on hills anymore. And I understand why some guys would run lower gears to get better off-road performance which of course means higher RPMs on the highway.

But my question is what is the problem in daily driving with the Jeep running in 7th gear (or 6th or 5th gear) going up hills when you put 37s on the factory 4.10 gears? In other words why would I want to see 8th gear going up a decent grade or even a mild grade? I just don't see a problem running in a lower gear going up hills. After all I am not going up hills full time, I am going down hills half of the time! :)
 

JTCO

Meme King
I think you guys are missing my question. I understand that when you put bigger tires on the factory gears that you raise the overall gear ratio which lowers RPMs on the highway, which means you probably can't pull high gear on hills anymore. And I understand why some guys would run lower gears to get better off-road performance which of course means higher RPMs on the highway.

But my question is what is the problem in daily driving with the Jeep running in 7th gear (or 6th or 5th gear) going up hills when you put 37s on the factory 4.10 gears? In other words why would I want to see 8th gear going up a decent grade or even a mild grade? I just don't see a problem running in a lower gear going up hills. After all I am not going up hills full time, I am going down hills half of the time! :)

Agreed. Not really a big deal. I always run lower gears on hills anyway so the motor doesn't have to work as hard.
 

NFRs2000NYC

Member
I think you guys are missing my question. I understand that when you put bigger tires on the factory gears that you raise the overall gear ratio which lowers RPMs on the highway, which means you probably can't pull high gear on hills anymore. And I understand why some guys would run lower gears to get better off-road performance which of course means higher RPMs on the highway.

But my question is what is the problem in daily driving with the Jeep running in 7th gear (or 6th or 5th gear) going up hills when you put 37s on the factory 4.10 gears? In other words why would I want to see 8th gear going up a decent grade or even a mild grade? I just don't see a problem running in a lower gear going up hills. After all I am not going up hills full time, I am going down hills half of the time! :)

I guess it depends where you live. I've driven over some passes in colorado where you can do 70....IF your vehicle can physically do it...and my JK couldn't even do 55. The JL with so many extra gears could, so instead of being in say 7th, it would have to sit in 5th. Technically, there is no difference in performance, just that your transmission will behave as a 5-6 speed instead of the 8 speed you paid for. Ideally, I would want to regear my future JL so that it performs as if it were stock...which seems to be 5.13s for 37s. If the rig would be in 8th on a flat road on stock tires, I'd like it to be in 8th on a flat road at 75mph in 8th, 7th up a slight grade, and 6th for a medium grade. Without a regear, you'll be at 7th, 6th, and 5th respectively. Not the end of the world nor will I be in a hurry to regear....it will probably be the LAST mod on my rig.
 

OverlanderJL

Resident Smartass
I think you guys are missing my question. I understand that when you put bigger tires on the factory gears that you raise the overall gear ratio which lowers RPMs on the highway, which means you probably can't pull high gear on hills anymore. And I understand why some guys would run lower gears to get better off-road performance which of course means higher RPMs on the highway.

But my question is what is the problem in daily driving with the Jeep running in 7th gear (or 6th or 5th gear) going up hills when you put 37s on the factory 4.10 gears? In other words why would I want to see 8th gear going up a decent grade or even a mild grade? I just don't see a problem running in a lower gear going up hills. After all I am not going up hills full time, I am going down hills half of the time! :)

Do you buy pants with two legs and only use one or do you use both? Do you buy a dozen eggs and only use the first six and throw the rest in the trash?


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wwood

New member
Do you buy pants with two legs and only use one or do you use both? Do you buy a dozen eggs and only use the first six and throw the rest in the trash?


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Good try guys, but I can't buy it! :)

I am not giving up anything- we use all 8 gears every day! As I said in my first post our Jeep runs in 8th gear just fine on flat roads. It runs in 7th on mild grades and 6th on steeper grades but so what? The transmission is supposed to downshift on hills to keep the Jeep in it's efficient power band. Why do you want to drive in 8th gear going up hills? In order to pull 8th on a decent hills I would need to spend big money to regear. That seems wacky to me because it gets me nothing and I lose the higher gear ratio which produces the best gas mileage during most driving conditions. Our Jeep is a daily driver and spends 90% of its time on the road, not rock climbing. And as I said before when you go up a hill you also come back down at some point during which lower gears just suck more fuel.
 

JLSahara

Member
I’m speaking from on-road situations, but I don’t mind if I don’t hit 8th fear at all. I rarely do hit it and I’m ok with that. I mean the new Jeeps jumped from 6th to 8 fears, which means you guys (old JK folks) probably didn’t hit 6th much before but now you’re hitting 7th gear pretty often now right? Isn’t that itself a positive?





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wayoflife

Administrator
Staff member
Do you buy pants with two legs and only use one or do you use both? Do you buy a dozen eggs and only use the first six and throw the rest in the trash?

I dunno - I think maybe it'd be more like buying a dozen eggs to serve 6 people breakfast with each getting 2 a piece. Installing new bigger tires would be like having an extra guest come by - do you go out and buy another dozen eggs just to feed that one person or do you maybe just scramble up what you got and make it work. Maybe not the perfect solution but if everyone's happy, there's no foul. :crazyeyes:

For me, running 37's on 4.10's has been way more than just doable like it was on the JK - I feel like I still have tons of power and still get decent MPG. Sure, I could upgrade to a higher ratio but at least for now, I just can't get myself to justify the cost.
 

OverlanderJL

Resident Smartass
I dunno - I think maybe it'd be more like buying a dozen eggs to serve 6 people breakfast with each getting 2 a piece. Installing new bigger tires would be like having an extra guest come by - do you go out and buy another dozen eggs just to feed that one person or do you maybe just scramble up what you got and make it work. Maybe not the perfect solution but if everyone's happy, there's no foul. :crazyeyes:

For me, running 37's on 4.10's has been way more than just doable like it was on the JK - I feel like I still have tons of power and still get decent MPG. Sure, I could upgrade to a higher ratio but at least for now, I just can't get myself to justify the cost.

I don’t have that many friends so I doubt anyone would just pop in lol


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doubletapdaddy

Caught the Bug
I dunno - I think maybe it'd be more like buying a dozen eggs to serve 6 people breakfast with each getting 2 a piece. Installing new bigger tires would be like having an extra guest come by - do you go out and buy another dozen eggs just to feed that one person or do you maybe just scramble up what you got and make it work. Maybe not the perfect solution but if everyone's happy, there's no foul. :crazyeyes:

It is New Year's day... have you slept yet, cuz I can't tell if this is sheer brilliance or a combination of sleep deprivation and alcohol. Either way, I'm loving it. 😆
 

DEFCON1

New member
I think you guys are missing my question. I understand that when you put bigger tires on the factory gears that you raise the overall gear ratio which lowers RPMs on the highway, which means you probably can't pull high gear on hills anymore. And I understand why some guys would run lower gears to get better off-road performance which of course means higher RPMs on the highway.

But my question is what is the problem in daily driving with the Jeep running in 7th gear (or 6th or 5th gear) going up hills when you put 37s on the factory 4.10 gears? In other words why would I want to see 8th gear going up a decent grade or even a mild grade? I just don't see a problem running in a lower gear going up hills. After all I am not going up hills full time, I am going down hills half of the time! :)

There is a ton of thought going into your statement. Haha. We just follow the old formula that you take your new tire size multiplied by current gear ratio divided by the old tire size to get your new desired gear ratio. So 4.10 x 37 / 32.7 = 4.63 OR 3.73 x 37 / 32.7 = 4.22. These are obviously not exact numbers and may not be the exact gear ratios available, so choose what makes the most sense. A little lower would get better mileage, a little higher would get more power.


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OverlanderJL

Resident Smartass
There is a ton of thought going into your statement. Haha. We just follow the old formula that you take your new tire size multiplied by current gear ratio divided by the old tire size to get your new desired gear ratio. So 4.10 x 37 / 32.7 = 4.63 OR 3.73 x 37 / 32.7 = 4.22. These are obviously not exact numbers and may not be the exact gear ratios available, so choose what makes the most sense. A little lower would get better mileage, a little higher would get more power.


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It would be a 33 not a 32.7. They don’t make a size 32.7.


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