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Old 02-24-2012, 10:44 AM   #31
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Im planning to go to duratracs wich are a smaller 35. Guys with rubi's who went to 35s before a regear and took it krawling please let me know your views.[/QUOTE]

a duratrac isnt exactly a rock crawling tire, you may want to look at other options

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Old 02-24-2012, 10:46 AM   #32
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Yep. I get email text alerts at the bare mention of the word combo and I've even got it set up now to do it for gas mileage. I'm thinking of changing the latter however because in inbox is always full.
I told myself a month ago "no more gas mileage threads." Then last night somebody posted one and Bam!

Like a fly to a turd.

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Old 02-24-2012, 11:07 AM   #33
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I hear you on the gas...it's only gonna go up, too. Especially after someone bombs the shit outta Iran.

The thing is, though...regearing can actually improve your mileage if, like me, you're already running 35's and are currently underpowered. Don't get me wrong, I'm not saying everybody should run out and slap 35's on their rigs and get gear changes...THAT won't help.

But with my CURRENT setup I'd expect my mileage to stay the same or improve slightly with lower gears.

If I hit on the right combo.

Maybe.

Wheeee!
I am going to be following your progress pretty closely!

An aside and mostly related:
If you're running higher RPMs though, how do you save MPG? I always thought (hey I've been known to be wrong ) higher RPMs meant more gas being fired into the pistons?
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Old 02-24-2012, 11:08 AM   #34
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Did someone mention "combo"?
Combo burrito.
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Old 02-24-2012, 11:30 AM   #35
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I am going to be following your progress pretty closely!

An aside and mostly related:
If you're running higher RPMs though, how do you save MPG? I always thought (hey I've been known to be wrong ) higher RPMs meant more gas being fired into the pistons?
You're right. But overall, if you're properly geared the engine will operate in much more of the "sweet spot" of the powerband, and won't struggle so much getting the Jeep up to speed.

If I see any gain, it won't be anything earth-shattering.
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Old 02-24-2012, 03:08 PM   #36
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still want the new wheels, anyone running stock tires with a 4.5inch backspace? Pros? Cons?

Im asking because im not set on the rise in tire size, but do want the option. So i'll need to go to a 17x9 with the 4.5 inch backspace. Or 17x9 with 5.25 backspace.

anyone?
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Old 02-25-2012, 12:47 PM   #37
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You're right. But overall, if you're properly geared the engine will operate in much more of the "sweet spot" of the powerband, and won't struggle so much getting the Jeep up to speed.

If I see any gain, it won't be anything earth-shattering.
So more power with less (or at least no more) gas.

This has got to be the best thread I've seen regarding regearing. I had given up wanting to know anymore and thought I was settled into downshifting and going about my business. And now this gear chart shows up. Where the hell has that thing been and how did I not ever see that? Is there a chart more specific for my '08? It looks like my 3.21s were minimal from the gitgo.

$1500 +/-, is that just parts or installed. Now I gotta start saving my money.
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Old 02-25-2012, 12:54 PM   #38
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So more power with less (or at least no more) gas.

This has got to be the best thread I've seen regarding regearing. I had given up wanting to know anymore and thought I was settled into downshifting and going about my business. And now this gear chart shows up. Where the hell has that thing been and how did I not ever see that? Is there a chart more specific for my '08? It looks like my 3.21s were minimal from the gitgo.

$1500 +/-, is that just parts or installed. Now I gotta start saving my money.
The chart has made many appearances here on the boards and it's been updated to show the ratios for the 12s now. If you have an 08 and 3.21s you need either:

4.56s or preferably 4.88s for a manual
5.13 for an auto. Yukon makes very good gears.
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Old 02-25-2012, 05:32 PM   #39
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The chart has made many appearances here on the boards and it's been updated to show the ratios for the 12s now. If you have an 08 and 3.21s you need either:

4.56s or preferably 4.88s for a manual
5.13 for an auto. Yukon makes very good gears.
I do have an 08 with 3.21 and 34" tires. I did find an older chart and it is quite a bit different. And like you said 4.56 puts me in the orange sweet spot. But 2929rpm seems too high for normal driving... maybe I'm not reading that chart right.

What should be the correct rpm driving down the highway at 60mph? Mine is probably 16-1700 rpm in 6th gear. A big bug hit can slow it down. I'm not complaining; I just have to keep an eye out for incoming bugs and downshift appropriately.
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Old 02-25-2012, 05:35 PM   #40
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So more power with less (or at least no more) gas.

This has got to be the best thread I've seen regarding regearing. I had given up wanting to know anymore and thought I was settled into downshifting and going about my business. And now this gear chart shows up. Where the hell has that thing been and how did I not ever see that? Is there a chart more specific for my '08? It looks like my 3.21s were minimal from the gitgo.

$1500 +/-, is that just parts or installed. Now I gotta start saving my money.
I'll dig up the chart for the 3.8L for you...gimme a few mins.

$1500 is for the whole deal...parts & labor.
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Old 02-25-2012, 05:39 PM   #41
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3.8L chart:


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Courtesy of jpoptrix on Flickr (I can't remember his username on here)
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Old 02-25-2012, 05:44 PM   #42
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I do have an 08 with 3.21 and 34" tires. I did find an older chart and it is quite a bit different. And like you said 4.56 puts me in the orange sweet spot. But 2929rpm seems too high for normal driving... maybe I'm not reading that chart right.

What should be the correct rpm driving down the highway at 60mph? Mine is probably 16-1700 rpm in 6th gear. A big bug hit can slow it down. I'm not complaining; I just have to keep an eye out for incoming bugs and downshift appropriately.
Okay, so with a manual, 3.21's and 34" tires, you're currently running at 1866 rpms @ 70 mph, which is pretty horrendous. I can totally understand the bug thing. Mild headwinds probably kill you, too.

If you went to 4.56's you'd be turning 2651 rpms @ 70, and would be good for pretty much all situations, except steeper/long hills, such as driving through the mountains. Since it costs $1500 to regear in the first place, I'd recommend going to 4.88's, UNLESS you think you might ever go to a larger tire size, in which case you should probably max out at 5.13. Then again, until you got the bigger tires, you'd be high on the rpms. Kind've a Catch-22.

With the 4.88's you'd be at 2837 rpms @ 70 mph, which really isn't bad at all. In fact, it would put your rpms @ 60mph pretty close to the optimum of 2700 rpms. As odd as it sounds, you might actually see a small improvement in your mileage, since your Jeep wouldn't be wheezing so hard to get up to speed, and maintain it, in higher gear.


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Old 02-25-2012, 06:07 PM   #43
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Why are you guys with 3.8L v6s even looking in a 2012 thread--

Rics/joe and I have been publishing 4.88/5.13/5.38 data for almost a year--where the hell have you been ???

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Old 02-25-2012, 06:10 PM   #44
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Why are you guys with 3.8L v6s even looking in a 2012 thread--

Rics/joe and I have been publishing 4.88/5.13/5.38 data for almost a year--where the hell have you been ???

--JIMBO
Some folks just gravitate to the winning team.
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Old 02-25-2012, 06:14 PM   #45
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Some folks just gravitate to the winning team.
You won't have to worry about anymore data from me !

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Old 02-25-2012, 06:21 PM   #46
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Good for you--you've got the hammer-
You won't have to worry about anymore data from me !

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Old 02-25-2012, 06:26 PM   #47
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Pretty well tells the story--don'tit !


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Old 02-25-2012, 06:29 PM   #48
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Pretty well tells the story--don'tit !

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Old 02-25-2012, 06:35 PM   #49
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Okay, so with a manual, 3.21's and 34" tires, you're currently running at 1866 rpms @ 70 mph, which is pretty horrendous. I can totally understand the bug thing. Mild headwinds probably kill you, too.

If you went to 4.56's you'd be turning 2651 rpms @ 70, and would be good for pretty much all situations, except steeper/long hills, such as driving through the mountains. Since it costs $1500 to regear in the first place, I'd recommend going to 4.88's, UNLESS you think you might ever go to a larger tire size, in which case you should probably max out at 5.13. Then again, until you got the bigger tires, you'd be high on the rpms. Kind've a Catch-22.

With the 4.88's you'd be at 2837 rpms @ 70 mph, which really isn't bad at all. In fact, it would put your rpms @ 60mph pretty close to the optimum of 2700 rpms. As odd as it sounds, you might actually see a small improvement in your mileage, since your Jeep wouldn't be wheezing so hard to get up to speed, and maintain it, in higher gear.
You guys are great. I found the correct chart and was coming back to say "nevermind". And I find you have already posted the correct chart. You too Chris. I know ya'll keep helping people out over and over and you keep on going over it again and again.

Wolf, I am on the verge of totally getting it but I have a few detail questions left and I will ask at the end here. I hope I'm not hijacking here... I think I'm still on topic. I love my tire size, 315/70R17. That won't ever change. I rarely ever drive over 60. If I do I'm speeding. I travel some hilly terrain but nothing like mountains. I'm a little surprised you suggest 2700 is optimum rpm. I assumed it would be much closer to 2000-2100. Well that goes along with what a mechanic at the dealer told me about shifting at over 4000-4500 to make the valves spin. He said that keeps deposits from building up on them. I can only hit 4000 in the first two gears or I'm speeding. As I was writing this I was thinking 4.10 is what I need but maybe 4.56 would be better like you suggest.

I only have one more question..for now. Is there an easy formula for converting rpm from that chart with different speeds? In other words, how did you figure 2700 @ 60?
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Old 02-25-2012, 06:51 PM   #50
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Why are you guys with 3.8L v6s even looking in a 2012 thread--
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Originally Posted by JIMBOX View Post
Rics/joe and I have been publishing 4.88/5.13/5.38 data for almost a year--where the hell have you been ???
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I don’t know why.
Maybe the 12s need their own section in the Wrangler Model Tech Forums.


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Some folks just gravitate to the winning team.

I might make this my new signature quote: "Some folks just gravitate to the winning team. - kbwwolf"
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Old 02-25-2012, 07:04 PM   #51
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still want the new wheels, anyone running stock tires with a 4.5inch backspace? Pros? Cons?

Im asking because im not set on the rise in tire size, but do want the option. So i'll need to go to a 17x9 with the 4.5 inch backspace. Or 17x9 with 5.25 backspace.

anyone?
You could always go with 33/12.5/17 (or whatever is closest). IIRC you still need 4.5 bs because of the added width.
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Old 02-25-2012, 07:13 PM   #52
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Why are you guys with 3.8L v6s even looking in a 2012 thread--

Rics/joe and I have been publishing 4.88/5.13/5.38 data for almost a year--where the hell have you been ???

--JIMBO
Just like yours, I read every word written next to rics avatar. Absolutely great wealth of knowledge.

You would have to admit last September when I was totally foggy about regearing and hearing things about mountains, 33s, 35s, gas mileage, towing, auto, manual, 4lo, 4hi, rpm, male or female driver etc., this didn't help me so much:

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Well, the 4.88 with 35 will be ok but just ok on older models. So AEV saying 4.10 with new motor will be like older models with 4.88 may be ok but not great. Most will tell you on here that 5.13 or 5.37 is actually were it should be to maximize power which means the new one should be closer to 4.88 to get full power back. Will 4.10 be ok, yes but then again it's just ok. It will not be idea just ok. But then again, ok is a lot less expensive then the true idea of 4.88 and 35's. 4.88 with the 42RLE is idea for 33's an barely idea then but not 35's
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Old 02-25-2012, 07:18 PM   #53
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You guys are great. I found the correct chart and was coming back to say "nevermind". And I find you have already posted the correct chart. You too Chris. I know ya'll keep helping people out over and over and you keep on going over it again and again.

Wolf, I am on the verge of totally getting it but I have a few detail questions left and I will ask at the end here. I hope I'm not hijacking here... I think I'm still on topic. I love my tire size, 315/70R17. That won't ever change. I rarely ever drive over 60. If I do I'm speeding. I travel some hilly terrain but nothing like mountains. I'm a little surprised you suggest 2700 is optimum rpm. I assumed it would be much closer to 2000-2100. Well that goes along with what a mechanic at the dealer told me about shifting at over 4000-4500 to make the valves spin. He said that keeps deposits from building up on them. I can only hit 4000 in the first two gears or I'm speeding. As I was writing this I was thinking 4.10 is what I need but maybe 4.56 would be better like you suggest.

I only have one more question..for now. Is there an easy formula for converting rpm from that chart with different speeds? In other words, how did you figure 2700 @ 60?
You're not hijacking at all, man. This is all on topic. Pie's trying to figure all this out for his rig, too.

As to your question...if there's a formula, I don't know it. That's just a guess, based on the level of rpm increase btw gears and tire sizes, as to where your rpms would be at 60 mph w/4.88's. The chart's not really set in stone, either.

Also, when I said "optimum rpm", I was referring to the blue part of the chart, basically the performance part.

It sounds to me like you'd be happy with the 4.56 gears; I just hesitate to say go in that direction, since one of the cardinal rules of a gear change is to NOT end up undergeared, given the $$ involved.

Then again, you know your driving habits better than anyone else.

Lemme also add that, with my rig (3.73's & 34" tires), I've gone round and round over whether to get 4.56's or 4.88's, and that's with the 3.6L engine.

So far I'm leaning toward the 4.88's...but as I said in an earlier post, I do go through the mountains quite a bit.
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Old 02-25-2012, 07:23 PM   #54
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Just remember when looking at the chart that the tire size is not your tire size but what the tire is on the Jeep[ and compressed. So for the most part you need to subtract one inch. So if you have 33" you should look at the 32's number. You will use the same number you use to program your ECU after tire upgrades to correct speedo
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Old 02-25-2012, 07:26 PM   #55
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You know what...I clean forgot about this gear calculator:

Here's a link: Gear Ratio Calculator

It works like this...the values I currently have plugged in are for a 2012 auto. If you know (or can find out) the gear values for your rig (2008?), then plug em in as in the example below, and it'll calculate your rate of speed and rpm for every gear. Pretty cool little link. I haven't broken this bad boy out for awhile.

Plug-In values for gear calculator (for 2012 manual):
It is much easier with an auto because you can select Dodge NAG1 and it fills out the 1st set of number for you.

For #1 - your ratios are:
1 4.46
2 2.61
3 1.72
4 1.25
5 1.00
6 0.797

For #2
High = 1
Low = 2.72

For #3
Ignore

For #4
I'm assuming 3.73....or 3.21....or put in what you want to play with.

For #5
Put in your tire size.

Calculate
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Old 02-25-2012, 07:32 PM   #56
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Unless I'm mistaken, your '08 manual has an NSG 370 transmission.

Lemme try one other thing, here...

EDIT: Okay, see post below.
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Old 02-25-2012, 07:52 PM   #57
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Okay Yella, here are the values you wanna plug into the link I gave you above:

Gear ratios for 2008 jeep jk manual transmission.: (Put 6 in # of forward gears) then fill out the ratios as follows:
4.4 in first, 2.6 in second, 1.7 in third, 1.2 in fourth, 1.0 in fifth and 0.8 in sixth. (don’t need reverse for the chart)...type these into the boxes.

Transfer case is either NV241 or NV241OR (Apparently Jeep used both that year...I tried both just a minute ago, and it hardly changed a thing in terms of the calculated mph/rpms.)...select either of these from the pull-down menu under 'Transfer Case Values'.

Fill in the gears you have, or are thinking of getting, etc.

Fill in the tire size in inches.

Once you hit the "calculate" button, scroll all the way to the last fields, where it will give you your rpms @ a given speed, etc.

Pretty informative little doohickey, IMO.
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Old 02-25-2012, 07:55 PM   #58
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Man kbwwolf, all I gotta say is: if you get anything greater than 4.10 you better get out of first gear fast
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Old 02-25-2012, 08:02 PM   #59
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Man kbwwolf, all I gotta say is: if you get anything greater than 4.10 you better get out of first gear fast
That manual for the '12 advises you to shift before 15 mph as it is, so...
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Old 02-25-2012, 08:14 PM   #60
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Originally Posted by kbwwolf View Post
That manual for the '12 advises you to shift before 15 mph as it is, so...
Especially when you drive like you just knocked off the President....

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want 35s

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