JL & JLU Wrangler Axle Gear Ratios: 3.45, 3.73, 4.10

[The Great Grape Ape]

It’s also interesting to note that not only is there a base and premium JT Scrambler trim levels (obviously still to be named [hoping Pioneer trim level is added to the naming mix]), but also..

..interesting that the Export version of the JT will get the 3L Ecodiesel while the export JL/JLU only gets the 2.2L diesel.

Sponsored

 

[BillyHW]

So is the Euro Pentastar going from 4,400 down to 3,500 now? Should they be scrambling to buy up the remaining JKs?

It does not make sense.

 

[The Great Grape Ape]

Bummer. Well maybe 3.45 will be adequate for most of us with the new 10 speed auto?

No Jeep is getting a 10-speed, and none of these are getting the Jeep’s 9-speed. All will be getting the ZF8 speed and a 6spd manual transmission as options.

In reality though the 1st gear ratio and overall spread on the latest ZF8s is better than on the Ford and GM 10 speed transmissions, with only a slightly shorter final drive / top gear OD of the ZF8 at 0.640 vs 0.636.

 

[chuck h]

So they’re trying to make the Sport more fuel efficient.. and then they cut its legs out from under it by upping the axle ratio from 3.21 to 3.45?

Would make more sense ifmit was required for the diesels, but both domestic and export get the 3.73, so that’s not it.

First gear ratio and overall spread will increase dramatically in the Automatic, so much so that in an auto the old axle ratio 3.21 on the ZF would’ve had a much better crawl ratio and better final drive than the current JK auto with a 4.10 axle.

My concern is that the reason they picked this ratio is to accomodate the manual transmission which they might not have been able to get as high a first gear ratio as the ZF’s 5.0:1 and as good an OD 6th gear or as full a ratio spread. 3.45 axle in the sport makes sense if the manual transmission’s first gear is 3.x-4.0:1 like in some Tremec 3160s and the gasoline version of the ZF S6, where 3.45 axle on a 4:1 first gear would still be a lesser crawl ratio than old NSG 6-speed and a 3.21 axle, you would need a 3.55 axle to almost match the old 3.21 if they weren’t able to get a better 1st gear.

Not reassuring from either a CAFE or manual transmission perspective.

For my daily driver it doesn’t have much of an impact as 3.73 was still the target even with the new automatic 1st gear and OD & Spread boosts, and for the cottage won’t make much of a difference, and a lower 1st gear than the current NSG would make a more relaxed 1st gear for puttering around town and leisurely country drives. But the implications are interesting.

Wow ape, you really have my head spinning right now. So, for the guys here like me, who have no idea what the hell you just said, can you explain to us what all of this info that came out today means in layman terms, for both the DD and for off-roasting capabilities? Some guys on here have said minor evolution is ok, just don't screw it up. Have they done anything to screw it up?

 

[The Great Grape Ape]

So is the Euro Pentastar going from 4,400 down to 3,500 now? Should they be scrambling to buy up the remaining JKs?

I dunno, and remember it’s not Europe, it’s Export including Australia, South Africa and the Phillipines as major export markets not in Europe.

It is odd, but as it’s an internal powerpoint presentation, they might have just out the same thing in both instead of doing conversion math, because the 4,400 lbs numbers is actually 2,000KG, and the top number is 2,300KG or 5,060 lbs.

So may have been just lazy conversion on the presenter’s part, otherwise I don’t know.

 

[BillyHW]

Is there no one here who knows an engineer at Jeep that can explain all the Wrangler towing oddities and anomalies?

 

[Armycop]

https://tiresize.com/gear-ratio-calculator/

The link above helps calculate tire size to gear ratio and what RPM range you will be in at speed. 3.73s should be fine with 35s and be perfectly driveable. 4.56 gears would be ideal for 35s. If you want to move up to 37s then 4.88 gears may be better. Most good 4x4 shops can do a regearing. Price is variable. I have seen prices ranging from $800 up to $1500 depending on where you take the Jeep.

 

[The Great Grape Ape]

Edit: Just a Warning up-front, this is pure Speculation, so read with an analytical/skeptical frame of mind...

Wow ape, you really have my head spinning right now. So, for the guys here like me, who have no idea what the hell you just said, can you explain to us what all of this info that came out today means in layman terms, for both the DD and for off-roasting capabilities? Some guys on here have said minor evolution is ok, just don't screw it up. Have they done anything to screw it up?

Don’t worry the axles aren’t screwed up, and the ZF8 would hide a lot of what they could even screw up. But there are some interesting implications of the choices, with basically a few things known and then a likely reason for the 3.45 axle choice.

Here is a LONG explanation that hopefully explains my thinking, I’ll put the ‘in short’ summaries of ‘what’ I think it means in bold for quicker reading for people who don’t care about the reasoning why.

We know the ZF8 transmission has a first gear of 5:1 which means they didn’t really need to change the axles to make it a better off-roader, or better able to handle bigger tires. The jump from shorter 3.59 first gear in the current NAG1 automatic would’ve made a 3.21 axle feel like a a much higher ratio giving an equivalent crawl ratio of a 4.47 axle. So that crawl ratio improvement for off-roading or bigger tires isn’t the reason for the change, but it will be the major beneficiary of that change.

Even the CommandTrac and SelecTrac transfer cases with their 2.72:1 4LO will have great crawl ratios (or downhill descent control ratios as I use them in 1st; where in the new Auto a ZF with CommandTrac would almost have the same crawl ratio as the old Auto with the Rubicon transfer case (13.6 multiplier vs 14.36 multiplier before looking at axles). Of course torque converter also plays a role, but these are just the ratios.

The outcome/result of that change is better off-road capabilities on the Auto and more easily getting larger tyres moving, and also a much quicker accelerating Wrangler than previously on all trim levels of the Wrangler, but...

..at a theoretical reduction of highway efficiency, although for the Wrangler it’s less about final drive ratio, than keeping the engine in a nice HP RPM level to overcome aerodynamic drag. So the impact to HWY efficiency may be minimal just because a low axle ratio and low final OD 8th speed might have led to a mathematical ratio that puts you below usable HP, and the benefits of the 8speed’s top gear may be lost on the 3.45 sport, but very well appreciated by the Rubicon’s 4.10.

So, in short the higher axle ratio for the base sport means improved off-roading, quicker acceleration, and better able to run bigger tires out of the box, and on the automatic this is even more so for all trim levels; but.. at a possible reduction in maximum theoretical fuel economy if we aren’t already hitting an aerodynamic wall/max.


Now for the POSSIBLE Negative implication of the 3.45 axle as the lowest possible option, and THIS is just a concern and Pure SPECULATION on my part so don’t start worrying until the JL actually gets her because this is where there is a Giant question mark regarding the manual transmission and it’s characteristics, whereas the previous was based on more reasoning of the known elements (ZF8, transfer case, axles) and their application.

So.. thinking of how one would operate the manual transmission and what one would want from the new 6spd in a Wrangler application, you would focus on 4 things related to the choice of axle ratios, off-road crawling capabilities, getting bigger tires moving/accelerating, HWY fuel economy, and then something unique to the manual transmission, how quickly & comfortable holding first gear through the RPM range is and relatedly how it goes through the other gears along the way to 6th.

Now for off-roading and tires you want higher axle ratios to make it easier to crawl and to use the multiplier effect to get bigger tires moving with less effort. However for fuel economy the reverse is in effect where ignoring torque curves and HP requirements, a low final drive ratio should yield better highway mileage allowing lower RPMs because you need few input revolutions to turn the wheels on the pavement through the same distance. However this is where the torque curve and HP requirements come in, because in order to overcome wind resistance as well as rolling resistance and drivetrain losses/resistance you need a specific amount of HP, so in order to generate XXX HP to go a certain highway speed you might need to leave that efficient low RPM mathematical ideal anyways, and be running at a certain RPM. This works both ways, obviously more soeed mean more HP, and also a high axle ratio like the 4.10might also mean more work to get the input high enough to make the axle run at HWY speeds.

However you have a diminishing rate of return so even if you had a 2.00:1 axle and a 12-speed auto with 0.500:1 top gear OD , you would still need the engine to spin enough to maintain a certain HP that can be multiplied, and very low in the RPMs the power drops off a cliff, so you can only go so low. Now while the new Pentastar should get better low end torque with an increase of 15% below 1,500 RPM, and shifting the torque curve earlier by 300 RPM, and this should help with getting better MPG from better HP at lower RPM (knowing HP=tq x RPM) and will play well with the better OD top gear in the ZF8, but again it’s just a mild bump, and will again drop off a cliff at a certain point. So the impact of 3.21 to 3.45 might not matter as much to the HWY speed as both might be more than enough to keep the engine in the RPM sweet spot for maximum efficiency.

In the Cherokee’s ZF 9speed’s very high 9.8x spread (vs ZF8’s 7.8) and extremely tall top OD gears 0.48 9th and 0.58 8th (vs ZF8’s 0.64 8th) means that 9th is rarely ever used by the transmission & ECU and even when manualy selecting 9th even slight variations make it difficult to hold that gear without feeling the need to shift. Now if the 6 manual has an extremely tall OD 6th like the one SUV Tremec 3160 option’s 0.60 6th gear, then the 3.45 axle would help make it a more usable gear to keep the engine in that sweet spot. Now the drawback is that manual 6speeds with very tall OD gears also have very tall (lower number) 1st gears as well, in the case of that particular SUV Tremec 1st gear is 3.35 to 1, which is lower than the current automatics 3.59:1 and way WAY lower than the 4.46:1 of the current NSG manual transmission. Which means you are losing load-end grunt in order to make that tall OD gear work, and are increasing the axle ratio to compensate for both (but not enough to make up for that huge shortfall from the current 6spd’s crawl ratio).

Now the fourth item on the list is how comfortable the axle + transmission ratios are going through the gears, especially the always quick shifting out of 1st which is made quicker with a higher rater, and longer with a lower gear ratio. Now if the engine were new and completely different then you could say it matches the engine characteristic, but the engine’s top end is still the same, the main change is down low so the impact is less. Now admittedly the 3.45 doesn’t change that that much, and quick & short shifting is nothing new for the people with 3.73 and 4.10 axles already and for this that doesn’t change, but the implication is there in light of other aspects we learned from the owners manual, principally the recommended shift points which remain the same for 1st to 2nd and 2nd to 3rd, but are grealy increased speed for 3-4, 4-5, and 5-6. This implies that the upper gears are noticeably taller than before and that the change occurs around 4th gear, which in the case of that SUV example I mention above has 4th gear as the 1:1 direct drive gear, whereas the other Tremec options and the current NSG all of them have 5th gear as the 1:1 direct drive. Meaning that that manual option has 2 OD gears in the form of 5th and 6th. Now in order to keep the driving experience good for something that favour OD gearing at the expense of 1st gear, you would want to give it a bit of a boost by upping the lowest option’s axle ratio from 3.21 to 3.45 making it a bit smoother driving experience. So in this case the axle and 1st and OD act in concert to deliver a ‘middle-ground’. Had the manual transmission ratios been anither Tremec SUV option or the ZF6, then they would both have higher 1st gear ratios along with lesser but still good OD gears (and close to the old NSG it’s replacing), so with a bigger 1st gear and good OD gears, then you would expect the exact opposite to happen to axle rarios, either they would remain the same, or go down to improve MPG while being made up fomby the better 1st gear crawl ratio, and that lowering of the axle ratios would make for a more usable 1st gear. That’s was concerns me that that 1st gear ratio has suffered significantly enough in the effort to provide good OD gears that a 3.45 axle is now required.

So again in short, in light of all the other efforts to increase MPG and all the benefits of the ZF8 transmission, the likely reason that the base axle ratio has been increased from 3.21 to 3.45 is because the manual transmission they picked likely has had to trade off good upper gear OD ratios for lowering the first gear / crawl ratio, and thus to keep the driving experience good enough for acceleration etc they had to increase the axle ratio to compensate instead of leaving it the same or even lowering it as one would expect if they were deriving efficiency from the axle and not the transmission.

(FYI, the Dana M180 axles supports 3.07 and higher, the M200+ support ratios starting below 3.0:1 so availible options for the new axles is not the limiting factor).


* Anywhooo, while I know the above is over-simplifying things for people who want to disucss it even more technically, and I am taking leaps between steps, but... hopefully that helps explain what I was trying to convey, otherwise.. it’s a lot of typing for nothing.


Again This is just EXTREME SPECULATION on my part and I’m not just jumping to conclusions, I’m speeding to them in a Dodge Demon, So DON’T get worked up by this until the full details and JL itself actually arrives in a few days/weeks

 

[The Great Grape Ape]

https://tiresize.com/gear-ratio-calculator/

The link above helps calculate tire size to gear ratio and what RPM range you will be in at speed.

That’s a nice quick rough guide, but it doesn’t really take the transmission differences into account (along with a few other aspects like engine characteristics & drivetrain efficiency), it is important to note that the chart is based on a direct drive 1:1 ratio to achieve 65MPH, so that would usually be 5th in the current JK 6spd manual transmission 4th gear in the current 5spd auto, and possibly either 4th or 5th in the new manual transmission (as I mention above) and 6th in the ZF 8spd transmission.

Now if the transmissions were close in ratios then it becomes a pretty good universal guide and you can expect slightly lower RPMs in higher OD gears.

You can manipulate the graph though to compensate for the variation, by considering/calculating in the same way that lowering the transmission’s OD ratio(s) from 1:1 would be like increasing the axle ratios by an equivalent amount (although not exact since system losses along the way might change asymmetrically it should be nearly and in most cases will be the same). For example the 6th gear in the current NSG370 at 0.84 would be equivalent to a 1.19 (ie 1 divided by 0.84) multiplier over a 1:1 direct drive, so apply that 1.19 times the axle ratio in the direction of either fuel economy or power you were looking for at the desired RPM at 65 MPH HWY speed. Unfortunately you can’t do the same for calculating different speeds as it’s a non-linear progression.

 

[WXman]

Looks like a JLU Sport tips the scales at 4,395 lbs. That's pretty heavy.

I love the fact that they are going with 3.45 axle gears standard. Combined with the 8-speed auto trans. ratios that'll be a NICE pulling power down low, with great cruising MPG ability on the interstate.

Edit: I crossed the wrong rows in the chart. Looks like the weight is a bit less than that. Also, looks like there's already a thread that did the same thing. Oops.

 

[The Great Grape Ape]

Hi speed test is 80, and the test isn’t a static one so the effect across the spread would benefit a lower axle ratio in the Sport, and then moving the other options down. And real world wil matter for other markets. Also real world even for reviewers will matter more than upping the crawl ratio on the Sport. The Rubicon crawl ratio will already be jacked up for the reviewers and marketers to trumpet, so the Auto sure doesn’t need the low end in the spoort, but it the manual does then that says something.

Given that the sport is coming with bigger tires (and also in the 8-speed case taller top gear), it was obvious that they needed to have numerically higher gearing on the sport.

The Sport doesn’t get bigger tires it’s already commonly on its alternate option 255/75/R17s like my Sport at the cottage, it just loses its smaller ones. The Rubicon is the only one currently in th sytem getting bigger tyres. And the top OD gear (8th) on the ZF8 is not that high, but also isn’t a limitation the way it would be in a spread restricted transmission like most 6-speed manuals.

On the Sahara and Rubicon, with the marginally bigger tires, no change was needed.

No, need for either to change, yet they DID change the Sahara which loses the 3.73 for gasoline models? Only the Rubicon gets the 3.73 & 4.10, and realistically for the auto doesn’t need the 4.10 as it can already best the previous crawl ratio with just the 3.73. However the manual on the other hand remains the question mark.

Realistically the dropping of the 3.21 and 3.73 option (on models that already uses it in a D44 it already uses) instead of dropping the configuration limited by default 4.10 option for the majority of the fleet is odd, especially when crying MPG improvements all refresh cycle.

Again it would make sense if they didn’t have the ratio option or weren’t able to configure, but the Sport, Sahara and Rubi all get the 3.73 in diesel form, but no other? Does that imply axle upgrades on all diesels or do the artificially restrict the ratios.

It’s very odd development in light of the 3 options they had and the 2 they kept and the one they changed. Adding the 3.45 is fine, but I think it fits better as a middle option not as the low end one, because the ZF8 and the equivalent Tremec SUV 6MT with the 5.0 1st gear both could’ve made p for the low end in spades. So doubling down low end at the cost of efficiency is odd, unless there are other challenges in the one question mark that remains.

 

[The Great Grape Ape]

I have yet to meet a Sport (or Sahara) owner that is keeping their Wrangler stock that wasn’t looking for better fuel economy, even though they didn’t understand what any of this had to do with MPG.
The people who even know what gear ratios do and care about shorter gears are not buying a Sport and keeping it stock to begin with. And if the 3.21 gears are cheaper than the 3.45, then each and every one of the off-roaders looking to mod a barebones Sport would be saying give me the cheaper option, as I’m riping out the stock anyways. 3.45 is not keeping those people from modding their axles,

Again, the wrong market target for higher ratios and worrying about adding 35s a lift, etc. Better to focus on the MPG for the CAFE benefits so they can give the more hardcore people what they want without the excuse if CAFE/MPG considerations. Wrong option for the wrong segment.

As I said above, given that the Sport now has a bigger entry tire (or if you prefer lost the smallest tire), 3.45 is right on. But I have no interest in that.

No, you didn’t say entry tires, nice backtrack. And yes, you have no interest because the Sport is not for the people who are looking to put mods on a stock Sport especially if it loses the 3.73 option in the process. Even if your argument about tires wasn’t tired, the loss of the 3.73 option in the Sport and Sahara works against that thinking

In my case, I am only interested in Rubicon, auto and 4.1 (the option you said is not needed )- I hope it is offered. Since I'll run light 36" (real) tires, that makes it work both on trail and highway without a regear.

It’s not as needed, especially if your comparing to a JKU auto with stock axles. The bump in ratios in the ZF 8 is enormous, and the 3.73 + ZF8 would destroy the drive ratio of a JK Auto with 5.13 axle ratio. So yeah, for the areas to focus on it’s not as needed, though nice to have. The gasoline Sport needs a fuel economy darling more than the Auto Rubi ‘needs’ a 4.10.

 

[WXman]

I thought the Sport was getting 245/75-17 tires now? How is that "bigger" than a 255/75-17?

Shorter tires, deeper axle gearing, and deeper low to mid trans. gearing means a lot more RPM and less fuel economy in the city. However, it will drive MUCH nicer overall so the feel will be better.

Sponsored