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Discussion Starter #1
Anyone running duratrac 33" tires (believe mine are truly 32.5") with 4.56 gears? I was looking to regear to 3.73, but was suggested to go to 4.56 for my setup. I do occasional towing of a 2100lb boat/trailer setup weekends mainly, and not very far. This is also my daily driver, average stop and go traffic, and normally 50-70mph.

Will these be too drastic a change?

I was told mpg would actually increase, just hard to believe. Any pros or cons going 3.21 to 4.56?

Thanks everyone

I was also told the 3.6L was best candidate for it due to engine specs vs the 3.8L

I have the auto tranny
 

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I don't see your transmission noted in this therd or your profile.

I've made the switch from 3.21 to 4.56. I have the six speed and "35" inch duratracs (33.9" mounted) I find this set up to be ideal. At 70 mph, I'm just a hair over 2500 rpm.

That said, gas milage certainly did not increase. If my set up was with the auto or smaller tires the rpm would be higher at any given speed.
 

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Discussion Starter #3
I don't see your transmission noted in this therd or your profile.

I've made the switch from 3.21 to 4.56. I have the six speed and "35" inch duratracs (33.9" mounted) I find this set up to be ideal. At 70 mph, I'm just a hair over 2500 rpm.

That said, gas milage certainly did not increase. If my set up was with the auto or smaller tires the rpm would be higher at any given speed.
Hey thanks, it is automatic, and 2 door. They said at 70 I would be at about 2200 rpms.
 

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I am running 35" DT with a 2.5 inch lift and recalibrated on 3.73's. I am really happy with the performance and gas mileage. Have not really been on the highway that much to determine rpm ranges at 70 mph, but a good mix of city and rural road driving I have been getting 18.6 mph both calc by the computer and hand through 3 tanks of gas. I am heading up to Montauk this weekend so will have plenty of highway miles to see rpm ranges.
 

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4.56's seem really aggressive for 33's....especially on a 2 door auto.

3.73's and 4.10's would be fine. But I guess if you are going to make the jump, you might as well make it worth your while. You could easily run 35's, and even 37's with 4.56's on a +2012 auto.
 

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Discussion Starter #7
With 4.56? They lied! 3.6 auto with 4.56 and 33" will be over 2600 rpm at 70 mph
I'm not liking the sound and look of that. I wonder if 4.10 is better. I don't like the idea of higher rpms on 6+ cylinder engines, doesn't bother me on smaller engines
 

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Yup- I'd go 4.10s or 4.56s. Why spend all that money for little gain? The cost of the gears (parts) is about the same- why don't they want to do 4.10s? Probably be perfect if MPG is a concern.
I ran 4.56s on my 305/70s for awhile and it was perfectly fine. Your RPMs are per the chart- you will run about 2500-2600 RPMs at 70 but a Jeep is not a Honda and it doesn't feel like one. The torque curve is flat as a pancake and the difference in power isn't much between 2200-2800. (Just "downshift" on the highway to this RPM to get an idea). However this will lower your MPG. But screw the MPG- my Jeep is so much more fun to drive. I'm now on 35s but if I didn't want the extra clearance I actually preferred 4.56s on the smaller tire. But I like a little oomph- 4.10s would be "fine" too.
http://www.wranglerforum.com/f33/3-21-gear-threads-summary-list-209000.html
 

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I ran the stock 32's for a couple weeks after the initial regear... I was at nearly 3k at 65 mph and 1, 3, and 5 gears were all but obsolete. The engine didn't seem "happy" at that rpm.. At speed. If you never plan on going over 33" I'd suggest 4.10s with the auto.
 

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Just gotta go your own calculations - it's easy! Check it out:

New Tire Diameter / Current Tire Diameter = Tire Diameter Ratio (TDR)

Your TDR will determine your RPM change (decrease in the case of larger tires) versus your stock setup.

New Gear Ratio / Current Gear Ratio = Gear Swap Ratio (GSR, not gun shot residue ,p).

The GSR will determine how much your RPM (engine speed) changes for a given road speed. For 3.21 to 4.56 it's....wait for it...1.42. That means if you were going X miles per hour at 2000 RPM before, you are now doing 2840 RPM now. That's pretty significant.

Lets say you are running a true 32" tire and you switch to a true 33" tire - that makes your TDR 1.03. I think you can see where this is going. 2840 / 1.03 = 2760 RPM. In other words, you are not getting much back with such a small change in tire Diameter.

Going to a true 35" tire means 2840 RPM becomes 2600 RPM.
Going to a true 37" tire means 2840 RPM becomes 2530 RPM.

I already did some other math this morning, so hopefully my brain didn't flame out and bolo any of that.
 

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Just gotta go your own calculations - it's easy! Check it out:

New Tire Diameter / Current Tire Diameter = Tire Diameter Ratio (TDR)

Your TDR will determine your RPM change (decrease in the case of larger tires) versus your stock setup.

New Gear Ratio / Current Gear Ratio = Gear Swap Ratio (GSR, not gun shot residue ,p).

The GSR will determine how much your RPM (engine speed) changes for a given road speed. For 3.21 to 4.56 it's....wait for it...1.42. That means if you were going X miles per hour at 2000 RPM before, you are now doing 2840 RPM now. That's pretty significant.

Lets say you are running a true 32" tire and you switch to a true 33" tire - that makes your TDR 1.03. I think you can see where this is going. 2840 / 1.03 = 2760 RPM. In other words, you are not getting much back with such a small change in tire Diameter.

Going to a true 35" tire means 2840 RPM becomes 2600 RPM.
Going to a true 37" tire means 2840 RPM becomes 2530 RPM.

I already did some other math this morning, so hopefully my brain didn't flame out and bolo any of that.

Or just use this. Its Friday after all. I hate to do math on a Friday. Found this to be pretty accurate.
Gear Ratio Calculator
 

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I test drove a 2013 2 dr rubicon last week it had a 6 speed and 4.10's with stock tires ~32" it was about 2500 rpm at 70mph.
 

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Discussion Starter #13
I ran the stock 32's for a couple weeks after the initial regear... I was at nearly 3k at 65 mph and 1, 3, and 5 gears were all but obsolete. The engine didn't seem "happy" at that rpm.. At speed. If you never plan on going over 33" I'd suggest 4.10s with the auto.
This is what I'm worried about, 2800 rpms just seems excessive for this engine. 600 extra rpms will cause premature and excessive wear IMO.

I still think 3.73 is way to go, I was just a little shocked they recommended 4.56. This is a jeep specialty shop too. I plan to stay on 33 duratracs for the life of vehicle, so not going bigger on tires.

I think 4.10 would be way to go if the Rubi people Seem to like that setup, seeing I have to pay the $1500.
 

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Discussion Starter #14
Just gotta go your own calculations - it's easy! Check it out:

New Tire Diameter / Current Tire Diameter = Tire Diameter Ratio (TDR)

Your TDR will determine your RPM change (decrease in the case of larger tires) versus your stock setup.

New Gear Ratio / Current Gear Ratio = Gear Swap Ratio (GSR, not gun shot residue ,p).

The GSR will determine how much your RPM (engine speed) changes for a given road speed. For 3.21 to 4.56 it's....wait for it...1.42. That means if you were going X miles per hour at 2000 RPM before, you are now doing 2840 RPM now. That's pretty significant.

Lets say you are running a true 32" tire and you switch to a true 33" tire - that makes your TDR 1.03. I think you can see where this is going. 2840 / 1.03 = 2760 RPM. In other words, you are not getting much back with such a small change in tire Diameter.

Going to a true 35" tire means 2840 RPM becomes 2600 RPM.
Going to a true 37" tire means 2840 RPM becomes 2530 RPM.

I already did some other math this morning, so hopefully my brain didn't flame out and bolo any of that.
Dang, thanks for this!
 

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This is what I'm worried about, 2800 rpms just seems excessive for this engine. 600 extra rpms will cause premature and excessive wear IMO.

I still think 3.73 is way to go, I was just a little shocked they recommended 4.56. This is a jeep specialty shop too. I plan to stay on 33 duratracs for the life of vehicle, so not going bigger on tires.

I think 4.10 would be way to go if the Rubi people Seem to like that setup, seeing I have to pay the $1500.
I have found that many specialty shops are still not familiar with the 3.6L so they are basing recommendations off earlier models that had lower power and worse trannies. The new auto is also head and shoulders better then the pre 12 autos so that makes a big difference too. Test drive a 4.10 Rubi and you will get an idea of what it is like. On a modern engine using good oil I doubt the long term effect of 2500 rpms vs 2000 rpms amount to much as far as wear goes.
 

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I test drove a 2013 2 dr rubicon last week it had a 6 speed and 4.10's with stock tires ~32" it was about 2500 rpm at 70mph.
I can confirm - my 2012 JK Unlimited Rubicon on its stock tires runs right about 2500 RPM at 70. 2000 RPM is about 57 MPH or so.

I might actually see better fuel economy out of 35 inch tires because then I could just run 5th gear at around 2450 rpm all the way to and from work at about 62 mph. Otherwise, I am around 2200 rpm or so, and the power for hills and such just isn't there without a down shift. Using cruise control, I actually see better economy running about 57 mph and 2500 or so RPM in 5th gear than I do at the same speed, 2000 RPM in 6th gear. Every time I hit a hill, I can bury the pedal...and still struggle to maintain speed. 62 MPH is really where I want to cruise anyway, so I end up doing a lot of gear box rowing to keep the JK moving forward without wasting fuel. The Jeep makes noticeably better power at around 2500 rpm...so, a tire choice that lets me run the speed and RPM combo I want the whole way to work might just balance out the extra weight/friction. Muah.
 

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I have found that many specialty shops are still not familiar with the 3.6L so they are basing recommendations off earlier models that had lower power and worse trannies. The new auto is also head and shoulders better then the pre 12 autos so that makes a big difference too. Test drive a 4.10 Rubi and you will get an idea of what it is like. On a modern engine using good oil I doubt the long term effect of 2500 rpms vs 2000 rpms amount to much as far as wear goes.
Agreed...
I think there /wasis a bit of a learning curve on the 3.6 and especially the W5A580 tranny. Sometimes people focus on the axle ratio, and forget the drive ratio.
4.10's on the 3.6/W5A580 are a lot different than 4.10's on the 3.8/42RLE
 

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I have found that many specialty shops are still not familiar with the 3.6L so they are basing recommendations off earlier models that had lower power and worse trannies. The new auto is also head and shoulders better then the pre 12 autos so that makes a big difference too. Test drive a 4.10 Rubi and you will get an idea of what it is like. On a modern engine using good oil I doubt the long term effect of 2500 rpms vs 2000 rpms amount to much as far as wear goes.
I think there are too many "specialty" shops that just get too much credit for stuff they just don't know about. They have the tools and the know how to install, but that doesn't mean they have the knowledge to know "what" to install.

4.56's on 35's is pretty aggressive, makes a nice crawler, not so nice on the highway. On 33's it just seems like a bad idea.

I have the 3.73 gears with 35's and a 6 sp tranny. Overall, I'd say that I'm very satisfied. I get 18 mpg over all, and 70 mph is 2050 rpm. If I had $$ to blow, I might be tempted to go to 4.10's but the cost would outweigh any benefit, I think. If you're re-gearing from 3.21, then I'd probably go to the 4.10, especially if you're going to run 35's. But if you're not going any larger than 33 (right! ;)) then the 3.73 will be good.
 

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This is what I'm worried about, 2800 rpms just seems excessive for this engine. 600 extra rpms will cause premature and excessive wear IMO.

I still think 3.73 is way to go, I was just a little shocked they recommended 4.56. This is a jeep specialty shop too. I plan to stay on 33 duratracs for the life of vehicle, so not going bigger on tires.

I think 4.10 would be way to go if the Rubi people Seem to like that setup, seeing I have to pay the $1500.
That sounds good (albeit expensive), but I totally disagree with your statement about 600 extra RPMs being excessive for the engine.

This engine was made to rev. It ain't even awake yet at 2K.

In fact, the same engine is sold in a vehicle that runs on 3.21 and 4.10 from the factory. The difference at speed in those gear ratios is around 600 RPM.
 

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I have a 2013 JKU 6 speed and went from 3.21s to 4.56s on 33" Duratracs. It was a great setup off road but a little aggressive on the highway. About 2750 RPMs at 70. Now I'm running 35" KM2s and its very nice on the highway and still a beast off road.


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