Proper gearing for 35" tires on '13 auto wrangler - Page 3 - JeepForum.com

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post #31 of 39 Old 05-03-2013, 10:16 PM
chrisjsmith4
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70 mph is 2400rpm. Speedo is corrected by procal; 6 gear on the manuals is 0.02 difference with new 5 speed. Barely noticable. My buddy has a 2012 2door with 4.56 6 speed 35's mine 2012 4 door 4.10's (factory). His will roast the 35's. He went from 3.21's so def improvement for cost. Spend the money on a cool summer top and other gadgets if your going to go 4.10. 4.88's will be too high rpms on freeway. If you really want to regear go 4.56.


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post #32 of 39 Old 05-04-2013, 09:41 AM
rha600
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Originally Posted by dualtjs View Post
Something is wrong with these numbers. The 5 speed in a 2013 has a 5th gear that's 0.79. If you have 4.10's and 35" tires, at 70 mph, you should be right a little more than 2,200 RPM. 2,500 RPM should be 76 mph.

edit to correct #s
Actually you're close. I forgot my Speedo is off by a little (which hopefully I just fixed with the Procal, need to go test it) but I was probably at more like 74-75. But considering 35" tires are never really 35" you can't be dead on so yeah, you're spot on.
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post #33 of 39 Old 05-05-2013, 06:30 AM
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Originally Posted by RogueStatus View Post
isnt the 6 speed manual trans with gearing gonna be different then my 5 speed auto with gearing?
Yes, but the OD gear is virtually identical in both. 1st & 2nd gear are where you'll see a difference, but it probably won't seem like a big one.
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post #34 of 39 Old 05-05-2013, 06:38 AM
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Remember to not even consider anything you read or hear concerning the 3.8 engine and the auto that went with it (2007-2011). The new Pentastar and new auto are worlds apart. No hate mail please as I’m not saying one Jeep is better than the other.
Not hate mail, nor do I want to go into a full on discussion of the two set ups (it's been flogged thoroughly), but from the actual data that I've seen, the biggest issue is the difference in Auto tranny gearing. Yeah, the 3.8L is a little lower in torque and HP, through 5,000 RPM, but not much. The PS kicks it up several notches after 5,000 RPM, but who drives in that range anyway? On the tranny issue, a 3.8L with with auto running 4.88's is virtually identical to the 3.6L with auto running 4.10. At 2,200 RPM, the 3.8L will travel 16 MPH in 1st and 67 in OD gear, while the 3.6L will travel 15 MPH in 1st and 67 in OD. Slight variations will occur due to actual tire size, etc, but the math works out to be virtually identical.
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post #35 of 39 Old 05-05-2013, 12:01 PM
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^^^ I had a í08 JKU (3.8), I identically set up like my 2012 (3.6) including tires, wheels, auto and even the color was the same. As for gearing it had 5.13s. This 2012 with 4.10s will out run and out pull the í08 by leaps and bounds. Gearing charts (math) donít tell the whole story.
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post #36 of 39 Old 05-05-2013, 12:24 PM
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Originally Posted by dualtjs View Post
Yes, but the OD gear is virtually identical in both. 1st & 2nd gear are where you'll see a difference, but it probably won't seem like a big one.
That table does not take the effect of torque coverters ability to multiply torque. Having said that a None rubi will notice this in low more than a Rubi going down steep hills. I see it all the time in a line of Jeeps heading down a steep trail. None rubis are on the brakes all the way down in low and in first even the sticks.

For a auto the new w580 is light years ahead of the later models 42le. Older autos would need the Rubi crawler add on to be in the same boat.

The Rubis today with 4:10 are the easier to setup with 35"s. Much less pain on the wallet. With cost of lockers and gears then labor. The ability to have deeper gears. slightly better axles. The rubi today is a rather low cost upgrade. Considering that not many have the money to buy a new Jeep then put many thousands in upgrades to get it there. But then again few Jeeps realy see much off road when new. There are exception to this and forums tend to have more of those type. Compared to the many that never would post here. they bought a Jeep for its looks.

The only thing left on the road that still looks like and is better than ever is the Icon of Jeep.

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post #37 of 39 Old 05-05-2013, 01:57 PM
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Originally Posted by 1222 View Post
^^^ I had a ’08 JKU (3.8), I identically set up like my 2012 (3.6) including tires, wheels, auto and even the color was the same. As for gearing it had 5.13s. This 2012 with 4.10s will out run and out pull the ’08 by leaps and bounds. Gearing charts (math) don’t tell the whole story.
Gear charts definitely don't tell the whole story, but math definitely will. The difference in torque is real and will result in what you describe. My point is that you have a major upgrade in gearing, that has to happen before you can get an accurate sense of the difference in engine performance. Said differently, from the dyno charts that I've seen, between the two engines, there's roughly a 13.5% difference in torque @ 2,400 RPM. In looking at the gearing of the 2 transmissions, 4.10 vs 4.88, to get to equivalent MPH at the same RPM, is a 19.0% difference (a difference that can be made up for $2,000 or less). I would be curious to see what the torque at the wheels difference would be with those 2 set ups.
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post #38 of 39 Old 05-05-2013, 02:02 PM
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Originally Posted by 222Doc View Post
That table does not take the effect of torque coverters ability to multiply torque. Having said that a None rubi will notice this in low more than a Rubi going down steep hills. I see it all the time in a line of Jeeps heading down a steep trail. None rubis are on the brakes all the way down in low and in first even the sticks.

For a auto the new w580 is light years ahead of the later models 42le. Older autos would need the Rubi crawler add on to be in the same boat.
My bad, I was strictly thinking of street driving. As you point out, there will be off road situations where the difference in 1st gear will be very real and noticeable, particularly in 4 low.
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post #39 of 39 Old 05-05-2013, 02:20 PM
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So i have 12, 6 spd with 3.21's what you guys are saying is that it will be slightly sluggish on the road but ill be fine. Then when i go offroading in 4 hi or 4 lo it will be noticeably sluggish.
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