Manual transmission gearing

[Maverick909]

My experience is in my Rubicon with 4.10 gears, if you have a Sport/Sahara with 3.45s then it isn't going to behave the same. In fact I know it sucks which is just one reason I didn't take delivery of my 24 Sport after I test drove it. I knew right off the bat I wasn't going to be happy with those 3.45 gears. They were "fine" for stock tires but I also knew I was going to 35s and they weren't going to cut it. I've had a truck with 4.10 gears on 35s in the past and know from experience that it works for me. In fact that truck didn't have a 5.13 first gear or 4:1 low range transfer case so the Rubicon should perform a lot better on 35 inch tires than that truck ever did. In fact I think the 4.10s are fine up to a 37 inch tire.

And I know for a fact there are people on this forum that think what I just said is blasphemy of the highest order and will tell you all day that you need 4.88s or lower for 37+ inch tires. Whatever.

Just because, I double checked...on 37s at 80mph with 4.10 gears you still turn more rpm than you do in a stock Sport at 80 mph.

If you’re driving flat surface roads with no hills and an automatic you can get away with 4.10 gears on 37’s I’ve had a lot of experience with 3.45, 4.10, and 4.88 with tire size ranging from the sports stock 31’s to 37’s. I still run 17+ mpg with 4.88 and 37’s on my Jeep. 4.10’s can’t climb a hill on the highway with 37’s without sitting at the 4500+ rpm range the whole time. If you like tuning your truck that way that’s fine but I can run 70-80mph on most the grades in California at 2500-2800 rpm with out the need to down shift with my 4.88’s. For Off-road hill climbing with a rubicon x-case 4:1 you can get away with it but itnwill
Feel closer to the sports 2.72:1 with 4.10 gear ratio. But when I wheel or am driving to wheel I spent my time in the higher elevation’s with long grades to get to where I wanna go wheeling.

as for the OP. Gear ratio depends on what you do with YOUR jeep. Daily driving it just a weekend warrior off roader. Etc. and what time if areas you drive the most at. If you’re looking for more pep then up the gears. But you will sacrifice a little mpg.

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[Rubi6mt]

If you’re driving flat surface roads with no hills and an automatic you can get away with 4.10 gears on 37’s I’ve had a lot of experience with 3.45, 4.10, and 4.88 with tire size ranging from the sports stock 31’s to 37’s. I still run 17+ mpg with 4.88 and 37’s on my Jeep. 4.10’s can’t climb a hill on the highway with 37’s without sitting at the 4500+ rpm range the whole time. If you like tuning your truck that way that’s fine but I can run 70-80mph on most the grades in California at 2500-2800 rpm with out the need to down shift with my 4.88’s. For Off-road hill climbing with a rubicon x-case 4:1 you can get away with it but itnwill
Feel closer to the sports 2.72:1 with 4.10 gear ratio. But when I wheel or am driving to wheel I spent my time in the higher elevation’s with long grades to get to where I wanna go wheeling.

as for the OP. Gear ratio depends on what you do with YOUR jeep. Daily driving it just a weekend warrior off roader. Etc. and what time if areas you drive the most at. If you’re looking for more pep then up the gears. But you will sacrifice a little mpg.

100% agree with this.

If you daily drive on pavement most of the time 4.10s and 37s is ok.

Where it was annoying was having to drop 2 sometimes 3 gears on a highway incline.

Where it really bothered me was when I was on the trails with my buddies trying to idle over some of the gnarlier rocks, I wasn't geared low enough and had to either slip the clutch a tad or go faster then I wanted to prevent stalling even with the rubi t/c.

I did it for about 2 months before I could scheduled regear to 4.88s and the CFII clutch kit with the heavier flywheel. All of a sudden the 3.6 felt a lot closer to the old straight 6 in low down torque and I could readily idle over pretty much any of the rocks I attempted.

Was a great combo until I sold it to get a bit more power.

Good luck!

 

[JimThomas]

I don't disagree, but just to explain what I mean. These charts are particular for my Jeep on 32s. The first one is the 3.45 stock gears. The second one is with 4.56. Look at the 3000 RPM column. I had a gap of 22 mph between 3000 RPM in 2nd and 3rd. That shrunk to 17 mph. Similar for all the other gears.

Road speed at given RPM in miles per hour
Gear	750 RPM	3000 RPM	6000 RPM
1	4	16	31
2	8	31	61
3	13	53	105
4	20	80	161
5	25	99	199
6	28	112	223

Road speed at given RPM in miles per hour
Gear	750 RPM	3000 RPM	6000 RPM
1	3	12	24
2	6	23	46
3	10	40	80
4	15	61	122
5	19	75	150
6	21	85	169

I have also done the math, posted it here before. But haven't re-geared.

My thought was, say I'm running 32 or 33" tires (blessed to have two JL's with manuals). With the 33" tires, maybe I'll use 6th on a flat stretch of the interstate, but probably 5th on the interstate. 4th on the highway. With the 32" tires, I will use 6th on the interstate, 5th on the highway, if it's flat. Else 4th. So in both cars, I've got one or even two gears that aren't worth using. So if I put a 4.56:1 or 4.88:1 gear into it, now I get to use 5th and 6th, but I probably never use 1st anymore. So what's the point? Other than easier on the clutch.

Based on your experience, it seems like putting the gears closer together in road speed is the point of re-gearing. What happened to your mileage when you re-geared? I'm mostly highway, summer time in the 32" 2DR I can get 24mpg without much trouble. The 33" 4DR also did that with the 32" tires, but when we went to 33" we dropped to 20mpg.

 

[azwjowner]

I have also done the math, posted it here before. But haven't re-geared.

My thought was, say I'm running 32 or 33" tires (blessed to have two JL's with manuals). With the 33" tires, maybe I'll use 6th on a flat stretch of the interstate, but probably 5th on the interstate. 4th on the highway. With the 32" tires, I will use 6th on the interstate, 5th on the highway, if it's flat. Else 4th. So in both cars, I've got one or even two gears that aren't worth using. So if I put a 4.56:1 or 4.88:1 gear into it, now I get to use 5th and 6th, but I probably never use 1st anymore. So what's the point? Other than easier on the clutch.

Based on your experience, it seems like putting the gears closer together in road speed is the point of re-gearing. What happened to your mileage when you re-geared? I'm mostly highway, summer time in the 32" 2DR I can get 24mpg without much trouble. The 33" 4DR also did that with the 32" tires, but when we went to 33" we dropped to 20mpg.

I wasn’t using 1st when driving between 15 and 65 mph anyway though. So it is an extra gear at normal driving speeds. The awkward gap between 3rd and 4th between 35-45 mph is gone now, which is huge. Can’t really comment on mileage as mine is an off-road Jeep with every gas tank.

 

[agpr2016]

You are 100% correct. But there's nothing any of us can do about it. The best alternative is to aggressively regear, which doesn't change the relative gear ratios, but moves the gears closer together in terms of vehicle speed. I'm running 4.56 on 32" tires, so my 2nd and 3rd are a bit closer together now in terms of speed and how soon I shift.

If the sport had higher gearing I'd get the sport. Considering the Willy's because it has higher gearing. Don't want to spend 3k to regear. However, if I knew I wouldn't like 4.11 and would regear anyway, I'd get the sport.

 

[Chuggy]

If you’re driving flat surface roads with no hills and an automatic you can get away with 4.10 gears on 37’s I’ve had a lot of experience with 3.45, 4.10, and 4.88 with tire size ranging from the sports stock 31’s to 37’s. I still run 17+ mpg with 4.88 and 37’s on my Jeep.

Found this comment while researching and trying to figure out whether I need 4.56 or 4.88 gears for my JL manual. Trying to buy parts asap and keep finding varrying information. I'm really leaning towards 4.56 but then I see someone running 4.56 with 35s and say they wished they had done 4.88...

I'm running 35s (35x10.5/17), on stock 3.45 gears with a 3 inch lift. I will never run higher than a 35" tire. I also don't plan on swapping for a rubi t-case anytime soon, if ever. I just don't wheel enough to justify the cost/work, and what I have works just fine. (I only recently put 35s on out of necessity- my 33s were worn, chopped, had some plugs. I wanted to regear at the same time but couldn't)

I'm usually on flat pavement for daily driving (eastern NC), but when I go wheeling its always in the mountains (NC/TN) and we travel to the mountains for leisure also sometimes.

I don't want 4.88s and then be overgeared and have worse mpg for my daily driving when really I'm not even wheeling it that often, but then again when I do take a trip, I put the Jeep to work.

I've read the 4.56 set up has a stronger pinion than the 4.88. I will be ordering Dana/Spicer parts. Also, I have M186 in the front and M220 rear, also read that for whatever reason some say don't go more than 4.56 on the M186. So much information. I just want to make a good choice for what I do, and also quality parts and longevity of the machine as a whole is important, obviously. (I've taken care of geometry correction, replaced front LCAS and front trackbar, will do the rear at some point, was careful with tire/rim choice to keep weight as close to factory as possible)

As far as added weight, I'll probably add rubi steel bumpers at some point but right now just have plastic. I'll be ordering a winch when I order my gears. I don't do any towing. I appreciate any feedback!

 

[azwjowner]

Found this comment while researching and trying to figure out whether I need 4.56 or 4.88 gears for my JL manual. Trying to buy parts asap and keep finding varrying information. I'm really leaning towards 4.56 but then I see someone running 4.56 with 35s and say they wished they had done 4.88...

I'm running 35s (35x10.5/17), on stock 3.45 gears with a 3 inch lift. I will never run higher than a 35" tire. I also don't plan on swapping for a rubi t-case anytime soon, if ever. I just don't wheel enough to justify the cost/work, and what I have works just fine. (I only recently put 35s on out of necessity- my 33s were worn, chopped, had some plugs. I wanted to regear at the same time but couldn't)

I'm usually on flat pavement for daily driving (eastern NC), but when I go wheeling its always in the mountains (NC/TN) and we travel to the mountains for leisure also sometimes.

I don't want 4.88s and then be overgeared and have worse mpg for my daily driving when really I'm not even wheeling it that often, but then again when I do take a trip, I put the Jeep to work.

I've read the 4.56 set up has a stronger pinion than the 4.88. I will be ordering Dana/Spicer parts. Also, I have M186 in the front and M220 rear, also read that for whatever reason some say don't go more than 4.56 on the M186. So much information. I just want to make a good choice for what I do, and also quality parts and longevity of the machine as a whole is important, obviously. (I've taken care of geometry correction, replaced front LCAS and front trackbar, will do the rear at some point, was careful with tire/rim choice to keep weight as close to factory as possible)

As far as added weight, I'll probably add rubi steel bumpers at some point but right now just have plastic. I'll be ordering a winch when I order my gears. I don't do any towing. I appreciate any feedback!

How fast do you cruise on the highway?

 

[JEEP4U]

4.88 or better for 3.6L MT on 37.......Anything less, the performance on I90 or I70 is just horrible....... if not embarrassing.

 

[M_Pluto]

Found this comment while researching and trying to figure out whether I need 4.56 or 4.88 gears for my JL manual. Trying to buy parts asap and keep finding varrying information. I'm really leaning towards 4.56 but then I see someone running 4.56 with 35s and say they wished they had done 4.88...

I'm running 35s (35x10.5/17), on stock 3.45 gears with a 3 inch lift. I will never run higher than a 35" tire. I also don't plan on swapping for a rubi t-case anytime soon, if ever. I just don't wheel enough to justify the cost/work, and what I have works just fine. (I only recently put 35s on out of necessity- my 33s were worn, chopped, had some plugs. I wanted to regear at the same time but couldn't)

I'm usually on flat pavement for daily driving (eastern NC), but when I go wheeling its always in the mountains (NC/TN) and we travel to the mountains for leisure also sometimes.

I don't want 4.88s and then be overgeared and have worse mpg for my daily driving when really I'm not even wheeling it that often, but then again when I do take a trip, I put the Jeep to work.

I've read the 4.56 set up has a stronger pinion than the 4.88. I will be ordering Dana/Spicer parts. Also, I have M186 in the front and M220 rear, also read that for whatever reason some say don't go more than 4.56 on the M186. So much information. I just want to make a good choice for what I do, and also quality parts and longevity of the machine as a whole is important, obviously. (I've taken care of geometry correction, replaced front LCAS and front trackbar, will do the rear at some point, was careful with tire/rim choice to keep weight as close to factory as possible)

As far as added weight, I'll probably add rubi steel bumpers at some point but right now just have plastic. I'll be ordering a winch when I order my gears. I don't do any towing. I appreciate any feedback!

Short answer? Just go with 4.88s.

Long mini-essay answer?
I have a JLUR and went with the factory 4.88 option and it's been totally fine. I can't speak for fuel efficiency of 4.10 vs 4.52 vs 4.88 as I've only ever driven with 4.88s, but I also live in a mid-high elevation area that is pretty hilly, and having semi-recently made a cross country road trip through the American flat lands, I can tell you with 90% certainty that makes a much bigger difference (especially the hilly part). I'm and am not familiar with what the conversion of metric to make-believe-units would be, but I get anywhere between 14.5L/100kms to 16L/100kms with my use case being 80% highway @ 100-120 kms speeds on average. Driving through the flatlands, my fuel efficiency went up to 12L/100kms on the American interstate. (In more practical terms, I can drive 180kms on ~ 1/4 tank of gas with mixed use of 60% highway and 40% city.)

I think the main difference you will notice more than anything is how torque-y it feels, especially in 1 low end at 1st & 2nd. 90% of the time I'm doing 2nd gear starts, because of how short 1st gear is. Other than that, she's been a dream any time I've taken her off road. When she was pure bone stock, no lift or anything (without even any with skid plates, which made it a bit of a nail-biter) she's done Top Of The World @ Moab. (Though while the gearing helped, I think lockers were what got me through it at the end of the day)

When doing research for my build and how I should build it out (since getting a MT was my one and only no compromise I needed to factory order) I asked around as to if I should get 4.88 or go with 4.10 and the general consensus/wisdom seemed to be this: if I planned on staying at stock tire size the 4.10s will do me just fine. However, if I planned to go with 35's or higher with a MT get the 4.88s. Anyone with an AT wouldn't need such low gearing, and 4.52 would be fine for them, but the MT seems has a different set of rules/needs or whatever.

Again, I will say to take what I say with a grain of salt as I don't have any experience with anything other than driving with 4.88, and I am in no way an expert, I just know what I've been told by multiple veterans who know their shit.

 

[roaniecowpony]

Wouldn't it be easier and cheaper to just take the rpm up higher before shifting? No matter the engine, they all have limitations. I bet if it was the same issue with a little red foreign sports car, we wouldn't be having this discussion.

 

[Chuggy]

How fast do you cruise on the highway?

Depends on how sick I am of people and how fast I'm trying to get to my destination... Good average is probably 70 max if I car about gas that day. 75-80 if I don't.

 

[Chuggy]

Wouldn't it be easier and cheaper to just take the rpm up higher before shifting? No matter the engine, they all have limitations. I bet if it was the same issue with a little red foreign sports car, we wouldn't be having this discussion.

I'm running 65 in 4th gear at about 2400. 70 in 4th gear at 2600. On flat ground in a straight line.

 

[azwjowner]

Depends on how sick I am of people and how fast I'm trying to get to my destination... Good average is probably 70 max if I car about gas that day. 75-80 if I don't.

Well, with 4.56 gears you’ll cruise at 2300 RPM at 70 and 2600 at 80. With 4.88 it’ll be 2450 at 70 and 2800 at 80. Your mileage is going to suck at 80 mph anyway. If you want slightly better mileage at 70, go for 4.56.

I’d go for 4.88, but that’s just me. You’ve posted about this before and people have elaborated at length. You just need to make a decision.

 

[Chuggy]

Well, with 4.56 gears you’ll cruise at 2300 RPM at 70 and 2600 at 80. With 4.88 it’ll be 2450 at 70 and 2800 at 80. Your mileage is going to suck at 80 mph anyway. If you want slightly better mileage at 70, go for 4.56.

I’d go for 4.88, but that’s just me. You’ve posted about this before and people have elaborated at length. You just need to make a decision.

Hey if you see an old thread on this with me in it feel free to reply to me on it or something so I can re-read. I know I posted months ago but just now getting around to buying what I need. I do tend to use the search feature quite well prior to asking

 

[azwjowner]

Hey if you see an old thread on this with me in it feel free to reply to me on it or something so I can re-read. I know I posted months ago but just now getting around to buying what I need. I do tend to use the search feature quite well prior to asking

https://www.jlwranglerforums.com/fo...ion-3-45s-lifted-trail-hwy-performance.127117

Several people in your thread there, including me, ultimately chimed in on your 4.56 vs. 4.88 ratio question.

You just have to get off the fence and pick one. You're not going to go wrong with either. It's a difference of 10% in your RPMs at your top speed. Since you seem concerned about gas, I say you'd like 4.56.

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