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Optimum Gears?

CarbonSteel

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I have had my Rubicon for a bit over a year now and have about 20K on the clock. Overall, there have not been any major issues, only minor ones—wandering steering and disconnected rear window defogger being the main items that come to mind, but there is one thing that really annoys me and that is on hills/inclines and high winds, it will not remain in 8th gear.

This leads me to ask the question (or pose) the thought as to why FCA did not gear the Rubicon (OEM 33” tires) with 4.56 gears as a minimum. I get that CAFE plays a role here, but based upon my driving experience, 4.56 gears would be a help not a hindrance. Based upon the inability for 33" and 4.10 gears to remain in 8th gear, I wanted to pose these questions:

-- Is 4.56 the optimum gear for up to 34” (true OD) tires?

-- Is 4.88 the optimum gear for up to 36” (true OD) tires?
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rubileon

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Are you running stock rims and tires? Which engine?

Mine even accelerates on inclines in 8th when going 60+ mph (low rpm).

What octane fuel are you running? Maybe the ecu downshifts to avoid detonation.
 
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CarbonSteel

CarbonSteel

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Are you running stock rims and tires? Which engine?

Mine even accelerates on inclines in 8th when going 60+ mph (low rpm).

What octane fuel are you running? Maybe the engine downshifts to avoid detonation.
Stock tires (33") with 3.6L, 4.10 gears and 8 speed transmission. I have used regular and premium unleaded and that makes no difference. I am not alone in this, many others have posted the same.
 

rubileon

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Stock tires (33") with 3.6L, 4.10 gears and 8 speed transmission. I have used regular and premium unleaded and that makes no difference. I am not alone in this, many others have posted the same.
So you don't like it when the vehicle downshifts from 8th to 7th but would rather have all of your gear ratios lowered by re-gearing?
 
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CarbonSteel

CarbonSteel

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So you don't like it when the vehicle downshifts from 8th to 7th but would rather have all of your gear ratios lowered by re-gearing?
You are missing the point. It downshifts into 7th with a head wind or a small hill-- it should not do that and it does it far more often than it should. I believe that 4.56 gears instead of 4.10 would minimize these instances with 33" tires.
 

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rubileon

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You are missing the point. It downshifts into 7th with a head wind or a small hill-- it should not do that and it does it far more often than it should. I believe that 4.56 gears instead of 4.10 would minimize these instances with 33" tires.
So you don't like the 7th because the engine stays at a higher rpm... and to get around that, you want the engine to stay at a higher rpm in all gears?
 

beaups

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So you don't like the 7th because the engine stays at a higher rpm... and to get around that, you want the engine to stay at a higher rpm in all gears?
People just want to see an 8 in the cluster for some reason. Even if it's the equivalent of what used to be 6th.
 
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CarbonSteel

CarbonSteel

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So you don't like the 7th because the engine stays at a higher rpm... and to get around that, you want the engine to stay at a higher rpm in all gears?
Still missing the point. It is not about the RPMs, it is the fact that a head wind can impact the vehicle enough to cause it to downshift. Lower gears would mean this would happen less frequently. I have never owned a vehicle where a headwind would cause it to downshift or never upshift. From my point of view, it seems like the gearing is suboptimal in conjunction with the tire size. Larger tires would make the condition even worse. Lower gears also mean more acceleration and torque.
 
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CarbonSteel

CarbonSteel

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Take it to the dealer. Sounds broken. Like I said, my 3.6 JLUR even accelerates on inclines in 8th gear. If a Sahara or Sport owner said, maybe it's normal.
Many have reported this issue so unless they are all broken...
 

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freddiegs

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Still missing the point. It is not about the RPMs, it is the fact that a head wind can impact the vehicle enough to cause it to downshift. Lower gears would mean this would happen less frequently. I have never owned a vehicle where a headwind would cause it to downshift or never upshift. From my point of view, it seems like the gearing is suboptimal in conjunction with the tire size. Larger tires would make the condition even worse. Lower gears also mean more acceleration and torque.
Take the top and doors off the wind wont have as much resistance :like:. But 8th gear was never intended to be a "passing gear". I totally understand what you mean that sometimes the wind will cause it to downshift but what do you expect to happen when your driving something that resembles a UPS truck. Also as you stated before CAFE probably plays a big role here also. Let the hair blow in the wind and tell your OCD to screw off! :LOL: I mean that in the joking way hopefully you don't get offended.
 

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I don’t like the fact that mine won’t stay in 8th as well. I’m running 35s and 2” inch lift. If it makes you feel better (it did me), 6th gear is direct 1:1 and 7th and 8th are both overdrive gears. So even in 7th you’re still in overdrive.
 
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CarbonSteel

CarbonSteel

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Take the top and doors off the wind wont have as much resistance :like:. But 8th gear was never intended to be a "passing gear". I totally understand what you mean that sometimes the wind will cause it to downshift but what do you expect to happen when your driving something that resembles a UPS truck. Also as you stated before CAFE probably plays a big role here also. Let the hair blow in the wind and tell your OCD to screw off! :LOL: I mean that in the joking way hopefully you don't get offended.
Well, on a 5,000 mile road trip, that would get as old as the 7th and 8th gear changeups. Just a little nuts to have a headwind effect a vehicle to the point of downshifting. I have owned many trucks in my time (which are also not very aerodynamic and they never downshifted (or would not upshift) in response to a headwind. :giggle:
 

oldcjguy

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Not sure how bad yours is, but I have the 2.0 and I don't think it's too bad. I look at it like this...
8th gear is enough for a steady cruising speed and to conserve fuel. The trans has 2 over drives AND the lower gears are very low. First gear in the auto is way lower than first in the manual or the old 5 speed. I don't have a problem with a second overdrive not being able to pull up a hill or go into a strong headwind. I'm driving a 4800 pound brick at 70mph with less than 300hp. I think with the combination of all the other gears and the torque converter that 4.10 is a good choice for 33s. Even if 8th is only used cruising flat and steady and squeaking out a little more mileage.

Now if 1, 2, 3, and 4 weren't so low and it effected low end performance I'd be singing a different tune. But with this trans we don't even hit 1:1 until 6th gear. But, like I said, I don't find it that bad on mine. It's not constantly hunting on the highway.
 

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First gear in the auto is way lower than first in the manual or the old 5 speed.
First gear on the JL's 6MT is lower than first gear on the 8AT.
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