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Old 08-24-2011, 02:18 PM   #1
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Please help me understand regearing.

I have a 2011 JKU which "they" say is geared wrong. As I understand regearing is helpful when going to larger diameter tires. However is regearing at all useful for the stock 29" tires? As I understand it will raise the RPM in 4 th gear thereby reducing MPG. Will it have any effect on the lower gears? Will it feel more peppy? I'm willing to sacrifice a little in MPG if it makes it drive better on the highway.

Confused,. help!

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Old 08-24-2011, 02:21 PM   #2
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1) who is "they"?
2) what kind of driving are you doing?
3) there is a world of opinion all based on specifics not clarified in your brief post

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Old 08-24-2011, 02:24 PM   #3
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You dont need to regear at all. Leave it alone. It cost a substantial amount of money to do that you dont need to spend if it doesnt need it.
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Old 08-24-2011, 02:42 PM   #4
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"they " is the people on the internet I do 99% highway. It is a stock JKU Sport.

If it doesn't need it then that's great.
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Old 08-24-2011, 03:04 PM   #5
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Look at these charts. One is for an auto transmission, one is for a manual transmission. Make sure you look at the right one.

If you have an auto transmission, you have 3.73 gears. If you have an manual transmission, you probably have 3.21 gears.

If you regeared so as to put your Jeep in the "blue zone," it would be noticably "peppier." Your RPMs will be higher at a given speed, which translates to power at the wheels. The difference would be substantial.

It may cost some mpg, but some--particularly auto transmission drivers--have noted that their mileage "around town" actually improves. The engine runs more efficiently.
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Old 08-24-2011, 03:17 PM   #6
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Jeeps typically regear when you go up in tire size, to maintain the same driving rpm they had before the tire upgrade. This helps keep the engine in it's factory powerband and makes the Jeep accelerate like it still has the factory tire size on it.
Hotrodders regear to get into their powerband earlier, or to get a quicker holeshot, or to put them at the ideal rpm going through the traps at the end of a dragstrip, or all of the above.
If you regear your Jeep with no other changes, you will turn a higher RPM in all driving scenarios, and will most likely lose some high rpm power, but the gains felt down low will make a nice difference. Power "gains" is actually false, you don't add any power, you simply change the gear multiplication to make better use of the available power. The trade off for better low rpm performance is a loss in top end power and a overall slower top speed, along with decreased highway fuel mileage (though steeper gears can actually IMPROVE stop and go mileage). 3 things of no real concern in a Jeep.
In the case of the 3.8, it doesn't breathe well up top in the rpm band, so you want to be careful about how much gear you add if you don't upsize your tires. The new 3.6 breathes very well up top, so I'm betting a gear swap in one of those will really wake it up.
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Old 08-24-2011, 03:26 PM   #7
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The op got the info in another thread of his. Thought with the AUTO- there was "room" to regear lower?

29" tires are small though and see no benefit with 3.73 already. Do you plan on bigger tires?

Edit: going by the charts, the op can go to
4.56. The 3.73 is very unhappy in the yellow ??
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Old 08-24-2011, 03:58 PM   #8
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yeah I had asked in another thread but I wasn't clear whether staying with stock tires would see an improvement. It seems from the chart I should go to 4.1 or 4.56 gears without sacrificing too much MPG with higher rpm. Are 4.1 or 4.56 gears common? Which would be preferred?
I have no current plans to change tire unless I could sell them and get a larger tire but this would be for looks only. Not a good reason I suspect.
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Old 08-24-2011, 04:26 PM   #9
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Quote:
Originally Posted by kinsale
yeah I had asked in another thread but I wasn't clear whether staying with stock tires would see an improvement. It seems from the chart I should go to 4.1 or 4.56 gears without sacrificing too much MPG with higher rpm. Are 4.1 or 4.56 gears common? Which would be preferred?
I have no current plans to change tire unless I could sell them and get a larger tire but this would be for looks only. Not a good reason I suspect.
Honesty is good

Buy some rubi take offs, 5 rims and tires for cheap, thats what I would do.

From what I read on here, go the lowest (highest number) you can get away with.
You have 3.73 so going to 4.10 would a small but noticeable change. But I have heard that the 4.56 gears are harder to come by, and more expensive-don't know why.

My Rubicon has stock 4.10 but it is stick, don't know how 4.10 works In the auto.

Dunno- see who else answers you.

I would go for the 4.56 if possible
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Old 08-24-2011, 04:31 PM   #10
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If you have an auto I wouldn't do anything less than 4.88. Preferably 5.13. Just get some Rubi take offs like kjeeper said.

This is an expensive change (~$1200). Guys that drive auto pre-2012 Rubis aren't happy with 33s and the stock 4.10s, and I know of at least two guys on this forum with autos and 33s that aren't happy with 4.88s. 5.13s--or nothing, stay as is--gets my vote. If you're going to do it, do it once.

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