Are 4.10s sufficient?

[CarbonSteel]

I'm not sure about where you come from, but 5-10 mph over the posted speed limit is normal freeway speed everywhere I've ever lived? So much so that a highway patrol sitting on the side of the road with the radar gun out the window won't budge if you're that close to the limit. Posted speed limits all over the west...75-80. You'll literally have semis pulling triples passing you in AZ if you're under 80mph. Even if you're trying to save fuel you can just draft one of them and still roll 80. On the east coast where you don't have straights that are dozens of miles long and you'd travel through 6 states before I can get out of CA in the same distance 80 might be rare. Here it is bellow average unless you are in the bay area, LA, or Sacramento. As far as mundane performance, the 5.38's made the jeep a half second slower 0-60 than it was with 4.10s, and that was still 7.5s which is hardly mundane for a 5k+lb vehicle on 38x13.50's if you ask me. I'd call cruising on the wide open freeway at 70 while everyone and their mom flies by mundane, but to each his own.

I have been to 49 out of 50 states so I am very familiar with highways and speeds, but let's be real here. Is a Jeep really intended to run at 80+ miles per hour for hours on end? I guess it can, but to use some of your words, I would opine that doing so would put you in the minority of Jeep drivers out there. You were over-geared without a doubt and in my opinion that in many ways has set up a very jaded perception of everything else that followed.

According to your numbers and mine, we are talking about a 200 RPM difference (or 3.07% of the entire useable RPM range) between 4.10 and 5.13 gearing at 85MPH in 8th gear (assuming that you were stating those RPMs in 8th) on an engine that has a 6500RPM redline. If we were talking 500+ RPMs difference that may be a different conversation.

What does that 200RPM buy you? Well no dragging out of gear shifts, no hunting of gears, the ability to maintain gears while on the highway--and make no mistake, it is not an MPG comparison that can be had because at those speeds MPG is going to suffer regardless of gearing. As I said before, here in CO, with 4.10 and 37s you would not see 8th at all unless going downhill. 7th and more likely 6th would be your top gear and 5th would be frequently seen and therefore would be running even higher RPMs with 4.10s than I would be running 5.13s.

I get that you like your combination and that it is working for you, but the differences between the RPM ranges versus the performance is not comparable.

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[Zandcwhite]

I have been to 49 out of 50 states so I am very familiar with highways and speeds, but let's be real here. Is a Jeep really intended to run at 80+ miles per hour for hours on end? I guess it can, but to use some of your words, I would opine that doing so would put you in the minority of Jeep drivers out there. You were over-geared without a doubt and in my opinion that in many ways has set up a very jaded perception of everything else that followed.

According to your numbers and mine, we are talking about a 200 RPM difference between 4.10 and 5.13 gearing at 85MPH in 8th gear (assuming that you were stating those RPMs in 8th) on an engine that has a 6500RPM redline. If we were talking 500+ RPMs difference that may be a different conversation.

What does that 200RPM buy you? Well no dragging out of gear shifts, no hunting of gears, the ability to maintain gears while on the highway--and make no mistake, it is not an MPG comparison that can be had because at those speeds MPG is going to suffer regardless of gearing. As I said before, here in CO, with 4.10 and 37s you would not see 8th at all unless going downhill. 7th and more likely 6th would be your top gear and 5th would be frequently seen and therefore would be running even higher RPMs with 4.10s than I would be running 5.13s.

I get that you like your combination and that it is working for you, but the differences between the RPM ranges versus the performance is not comparable.

I quoted current rpm in the XR with 4.56 and 35's, which is still on the lower end of gearing I'd choose. If we are talking 4.10s vs 5.13s on 37's, you'd be looking at a difference of ~550 rpm. Again not pushing toward redline or anything but significant for sure. Gear and tire selection being free, I'd likely go 4.88s and 37's. My point is the OP is used to 3.45s and 35s (definitely too tall), and some are telling him 4.88s or even 5.13s for 35s. In my experience that's too low. I'd say 4.56 for 35s, 4.88s for 37s, and save the 5.13s for 40's. You've stated that 5.38s was overgeared for 38s, that was literally only 50rpm more than your current set up at 80mph. 4.88s and 35s works out to about 15rpm more than 5.13s/37s. Again if you never drive over 75mph, go for it. If you tend to drive on the faster side, you will regret it in my experience.
My advice to the OP, or anyone trying to pick gears, is go test drive an XR. They are on most dealer lots these days. Free verification of if you want to go lower than 4.56, or higher, even if you're in the market for a 2 door. Get it up to freeway speed, as you would drive normally. Decide from there. If you're jumping into big tires and gears in the 5's, you don't have that option. If you just want to know how it will drive on 35's, that's free and easy.

 

[CarbonSteel]

I quoted current rpm in the XR with 4.56 and 35's, which is still on the lower end of gearing I'd choose. If we are talking 4.10s vs 5.13s on 37's, you'd be looking at a difference of ~550 rpm. Again not pushing toward redline or anything but significant for sure. Gear and tire selection being free, I'd likely go 4.88s and 37's. My point is the OP is used to 3.45s and 35s (definitely too tall), and some are telling him 4.88s or even 5.13s for 35s. In my experience that's too low. I'd say 4.56 for 35s, 4.88s for 37s, and save the 5.13s for 40's. You've stated that 5.38s was overgeared for 38s, that was literally only 50rpm more than your current set up at 80mph. 4.88s and 35s works out to about 15rpm more than 5.13s/37s. Again if you never drive over 75mph, go for it. If you tend to drive on the faster side, you will regret it in my experience.

550 RPM difference if you could run at 85 in 8th--is that possible with 4.10 gearing and 37's on anything other than downhill--not in my experience. My over-gearing statement is based upon your experience; I have stated this more than once for a 3.6L/ZF8:

33s = 4.56
35's = 4.88
37's = 5.13
38+ = 5.38

Recommending 35s and 5.13s would have to be some special use case as that would be too low.

4.88's and 37's work on flat ground and at sea level. I had them in Texas and they were ok--not as peppy as 4.88 and 35's, but still good. Once I moved to 7K elevation and lost 21% of my HP/TQ (which a 3.6L does not have 21% of anything to spare), they no longer worked. The gear shifts would drag out and it would hunt for gears on the highway making the driving experience far less than optimal.

I re-geared to 5.13 which solved it and I run about 150RPM more than with 4.88's. The BFGs I am running are short and my next set will likely be a different tire which most are slightly taller so I hope that is not enough to return the performance back to what it was with 4.88's.

Now, all of these conversations would go away if a 3.6L made about 350HP with 375lb-ft of torque which is the root issue around all of this...

 

[Zandcwhite]

550 RPM difference if you could run at 85 in 8th--is that possible with 4.10 gearing and 37's on anything other than downhill--not in my experience. My over-gearing statement is based upon your experience; I have stated this more than once for a 3.6L/ZF8:

33s = 4.56
35's = 4.88
37's = 5.13
38+ = 5.38

Recommending 35s and 5.13s would have to be some special use case as that would be too low.

4.88's and 37's work on flat ground and at sea level. I had them in Texas and they were ok--not as peppy as 4.88 and 35's, but still good. Once I moved to 7K elevation and lost 21% of my HP/TQ (which a 3.6L does not have 21% of anything to spare), they no longer worked. The gear shifts would drag out and it would hunt for gears on the highway making the driving experience far less than optimal.

I re-geared to 5.13 which solved it and I run about 150RPM more than with 4.88's. The BFGs I am running are short and my next set will likely be a different tire which most are slightly taller so I hope that is not enough to return the performance back to what it was with 4.88's.

Now, all of these conversations would go away if a 3.6L made about 350HP with 375lb-ft of torque which is the root issue around all of this...

The OP lives at 850' according to a quick search, in my opinion he'll be more than happy with 4.56s and 35s as that is still a massive jump from 3.45s and still quite a bit lower than even a stock Rubicon with 4.10s and 33s. Now if you're talking about spending $2500 to regear, and you think you might ever go to 37s, 4.88s would be liveable with 35s. Even if you only see 8th at 85 going downhill, you live in the mountains so logic would say 50% of the time it is downhill?

 

[Steph1]

If you're looking for an excuse to trade, go ahead and just do it.

However, if you're genuinely just annoyed by your current gear ratio/tire size/driving pleasure equation, by all means, you are $2G away from the total satisfaction that a reagear can bring.

It is one of those feelings that you have to experience to fully understand. Having your Jeep drive even better than it looks is priceless and before/after driving pleasure won't even come close to comparison. You'll have that grin on your face all the time again and it won't be because you're crossing path with a jeep sporting an angry grill .

Way too many heads in the sand here trying to convince themselves and others that the Rubi stock gearing is just fine for 35s. it's a price thing because it doesn't show.Offer it for $500 and they'd all be regeared. Yes 4.10s feel the hit of bigger tires and that is simple physical/mathematical logic. Bigger rolling mass and weight take a hit on all engines power.

 

[Zandcwhite]

If you're looking for an excuse to trade, go ahead and just do it.

However, if you're genuinely just annoyed by your current gear ratio/tire size/driving pleasure equation, by all means, you are $2G away from the total satisfaction that a reagear can bring.

It is one of those feelings that you have to experience to fully understand. Having your Jeep drive even better than it looks is priceless and before/after driving pleasure won't even come close to comparison. You'll have that grin on your face all the time again and it won't be because you're crossing path with a jeep sporting an angry grill .

Way too many heads in the sand here trying to convince themselves and others that the Rubi stock gearing is just fine for 35s. it's a price thing because it doesn't show.Offer it for $500 and they'd all be regeared. Yes 4.10s feel the hit of bigger tires and that is simple physical/mathematical logic. Bigger rolling mass and weight take a hit on all engines power.

Everyone quotes the math, without doing the math? A stock non-rubicon with 3.45’s and 32’s is geared identical to 4.10s and 37s. It’s simple math. I wouldn’t gear to 4.88s for 35s if you paid me the $2k (unless I was allowed to use the $ to buy 37’s immediately). This isn’t ”head in the sand” or about the $, this is 25 years of owning 15+ Jeeps, spending $100s of thousands of dollars in the process, 70k miles in JLs alone, geared 4.10, 5.38, and now 4.56 experience talking. Even if 4.10s and 33s is your definition of the gold standard for gearing, 4.27’s would be the match for 35’s, again math. Is it worth the effort to change gears for ~100rpm difference at a given speed, throwing your axle warranty out with it? Absolutely not in my opinion. Now if you can order your Jeep with 4.56s, they are definitely liveable on 35s but that is a different story.

 

[Steph1]

Everyone quotes the math, without doing the math? A stock non-rubicon with 3.45’s and 32’s is geared identical to 4.10s and 37s. It’s simple math. I wouldn’t gear to 4.88s for 35s if you paid me the $2k (unless I was allowed to use the $ to buy 37’s immediately). This isn’t ”head in the sand” or about the $, this is 25 years of owning 15+ Jeeps, spending $100s of thousands of dollars in the process, 70k miles in JLs alone, geared 4.10, 5.38, and now 4.56 experience talking. Even if 4.10s and 33s is your definition of the gold standard for gearing, 4.27’s would be the match for 35’s, again math. Is it worth the effort to change gears for ~100rpm difference at a given speed, throwing your axle warranty out with it? Absolutely not in my opinion. Now if you can order your Jeep with 4.56s, they are definitely liveable on 35s but that is a different story.

That is just mathematical, you forgot the physical part which is just as important. Adding 40-50lbs per corner and 2-3 inches of width has a huge impact on performance. It's not just about the new tire size/old tire size x actual gearing formula. I personally waited 3 years before regearing and would not hesitate to do it sooner. As said, the feeling of satisfaction is undescribable until you experience it. My Jeep with 4.56 and 35s turn the tires easier than it did the 32s with 3.45s and mpg is darn close to stock.

 

[Zandcwhite]

That is just mathematical, you forgot the physical part which is just as important. Adding 40-50lbs per corner has a huge impact on performance. It's not just about the new tire size/old tire size x actual gearing formula.

That math thing again…stock 285 KO2’s 58lbs, 37x12..50 patagonias 72lbs, 14lbs per corner is barely noticeable at best. Sure if you’re running a nitto 38x13.50, one of the heaviest tires on the market at 96lbs, you’ll be close to your 40lbs per corner. If you want to run a tire that heavy, on a heavy Beadlock where your combo is pushing 150lbs, you don’t need a regear you need 1 tons.

 

[c20040215]

Rotational mass is not as simple as 1+1 =2

 

[Steph1]

That math thing again…stock 285 KO2’s 58lbs, 37x12..50 patagonias 72lbs, 14lbs per corner is barely noticeable at best. Sure if you’re running a nitto 38x13.50, one of the heaviest tires on the market at 96lbs, you’ll be close to your 40lbs per corner. If you want to run a tire that heavy, on a heavy Beadlock where your combo is pushing 150lbs, you don’t need a regear you need 1 tons.

Add proper wheels for the tire size and you're not running 22lbs wheels anymore. unless you do things half way there too, IDK. Personally I chose to stay light and go with 17x8.5 BR wheels at 27lbs per corner. However, most other aftermarket wheels weight as much as 35-40lbs.

But it's ok, you won't know until you know.... A buddy of mine with a new Rubi was boasting at a meet that his Jeep was fine with 35s and stock gearing and swore it drove fine. I threw him my keys and told him to go for a spin around the block. When he came back, he said ''thank you and F?&% you, you just cost me $3000'', which is the price for a regear on a JL here in Canada.

 

[CarbonSteel]

Rotational mass is not as simple as 1+1 =2

Plus the added weight--I added about 1K. I weighed my Jeep not long ago and it was 5970, when combined with a 3.5" lift, the loss of power at altitude, 4.10s make zero sense, but they can work for some.

 

[c20040215]

Plus the added weight--I added about 1K. I weighed my Jeep not long ago and it was 5970, when combined with a 3.5" lift, the loss of power at altitude, 4.10s make zero sense, but they can work for some.

Plus having bigger tires means you probably have a lift, which adds wind resistance at higher speed. You always want to gear a bit higher to compensate those factors. Once the baseline is established, you look at your future plans and usages etc to decide if you want your gear to be more on the aggressive side or not.

 

[Zandcwhite]

The OP is talking about 35’s on a 2dr rubicon, which can be done at stock height, y’all are discussing 3.5” lifts, 37”+ tires, and an entire build of heavy armor and bumpers and god knows what else to add 1k lbs? And then factoring in living 6k+ feet above his elevation? As I’ve stated 20 times, slightly lower gears to make up for weight make sense. 4.88’s for a light 2dr on 35’s is not slight and it’s completely unnecessary in my EXPERIENCE, but you won’t know even if it’s spelled out for you.

 

[CarbonSteel]

Oh? We were? Somehow I got the impression we were talking about 50 reasons why you don't need to regear if you drive at 80+ MPH for hours on end versus the reasons why everyone else says that you should.

 

[J0E]

Rotational mass is not as simple as 1+1 =2

Rotational inertia is important for dragsters and insignificant for wranglers. It's just a factor at high acceleration, which wranglers don't have, especially in 5,6,7,8th gear high range. That's where mag's come from, originally dragster magnesium wheels, off the line, the lower mass at radius R, made a difference. Even with a dragster, it's insignificant compared to the mass of the vehicle. But any advantage is taken.

FWIW, my JLR 2.0 T on 37" KM3's with stock gears hit's 8th at 55, sea level. Going up the volcano I have hit 65 MPH, but typically 45 MPH is the fastest I go. At 45 MPH, 7th gear, level, console shows 30 MPG. Mine's a dedicated trail rig and get's 20.5 MPG, which is lowered by lots of low range crawling.

Add proper wheels for the tire size and you're not running 22lbs wheels anymore. unless you do things half way there too, IDK. Personally I chose to stay light and go with 17x8.5 BR wheels at 27lbs per corner. However, most other aftermarket wheels weight as much as 35-40lbs.

But it's ok, you won't know until you know.... A buddy of mine with a new Rubi was boasting at a meet that his Jeep was fine with 35s and stock gearing and swore it drove fine. I threw him my keys and told him to go for a spin around the block. When he came back, he said ''thank you and F?&% you, you just cost me $3000'', which is the price for a regear on a JL here in Canada.

Heavier tires are generally much stronger off road. Mass of entire vehicle is what matters. I don't care what my tires or beadlocks weigh, but I'm optimizing for crawling.

Everyone quotes the math, without doing the math? A stock non-rubicon with 3.45’s and 32’s is geared identical to 4.10s and 37s. It’s simple math. I wouldn’t gear to 4.88s for 35s if you paid me the $2k (unless I was allowed to use the $ to buy 37’s immediately). This isn’t ”head in the sand” or about the $, this is 25 years of owning 15+ Jeeps, spending $100s of thousands of dollars in the process, 70k miles in JLs alone, geared 4.10, 5.38, and now 4.56 experience talking. Even if 4.10s and 33s is your definition of the gold standard for gearing, 4.27’s would be the match for 35’s, again math. Is it worth the effort to change gears for ~100rpm difference at a given speed, throwing your axle warranty out with it? Absolutely not in my opinion. Now if you can order your Jeep with 4.56s, they are definitely liveable on 35s but that is a different story.

Just use my BT39.com (Big Tire 39") for the simple math.

> is geared identical to

that's what it does, compares anything you like.

The OP is talking about 35’s on a 2dr rubicon, which can be done at stock height, y’all are discussing 3.5” lifts, 37”+ tires, and an entire build of heavy armor and bumpers and god knows what else to add 1k lbs? And then factoring in living 6k+ feet above his elevation? As I’ve stated 20 times, slightly lower gears to make up for weight make sense. 4.88’s for a light 2dr on 35’s is not slight and it’s completely unnecessary in my EXPERIENCE, but you won’t know even if it’s spelled out for you.

That's all true but maybe they want to optimize for light to light wrangler drag races.

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