Won't hold highway speed in 6th gear

Corey6188

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Hey looking to get info on maybe some solutions for my JL to hold about 75mph on the highway. I have a sport altitude unlimited 6 speed with 34 inch KO2s and 3.45 gears. Also just installed a cold air intake. Speedometer reads about 70mph when I am going 75mph but unless I am behind a large vehicle to block wind the jeep will not hold that speed in 6th gear. Barely will hold that speed in 5th gear when climbing small hills. I am in east GA by the ocean and there are no mountains and is mostly flat. Will an axle back exhaust give me any more HP or are they just sound. Also would a programmer solve the problem.





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michail

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How does/did it handle stock wise?

Rubicons are limited to about 97 MPH and non-Rubicons are 110 MPH. Either of which is insane for the given aerodynamics.
 

FJL40

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I feel your pain….I took a trip to Grand Canyon from Phoenix recently and the hill climbs weren’t very fun in my 6spd JLR. You need to be in 4th gear at most when doing these inclines. Adjust as grade gets steeper (kick down to 3rd, 2nd, 3rd, etc…). I don’t know if it’s the tune or what, but a supercharger is on my todo list real soon. I also was told the tire speed rating is programmed in the ecu limiting your top speeds to prevent tire failure, not sure the accuracy of that though.
 

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I have a stock Rubicon and struggle to hold 6th with my 4.1 gears and 285/70r17’s. So your bigger tires and lower gearing aren’t surprising. Flat highway I do ok at around 70. I also have to kick down to 4th when heading up the mountain passes on US-2 or I-90.
Headwinds, forget it. Back to 4th.
 

kkarnage

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Hey looking to get info on maybe some solutions for my JL to hold about 75mph on the highway. I have a sport altitude unlimited 6 speed with 34 inch KO2s and 3.45 gears. Also just installed a cold air intake. Speedometer reads about 70mph when I am going 75mph but unless I am behind a large vehicle to block wind the jeep will not hold that speed in 6th gear. Barely will hold that speed in 5th gear when climbing small hills. I am in east GA by the ocean and there are no mountains and is mostly flat. Will an axle back exhaust give me any more HP or are they just sound. Also would a programmer solve the problem.
Personally I'd want to be on at least 4:10 gears for this kind of configuration. Having regeared a number of Wranglers with various wheel sizes, for a manual on 35's, I found 4.88 to be the sweet spot. Once you hit 37's, I found 5:13 to be optimal for my use cases.
 
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Corey6188

Corey6188

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How does/did it handle stock wise?

Rubicons are limited to about 97 MPH and non-Rubicons are 110 MPH. Either of which is insane for the given aerodynamics.
Not sure how it was stock. Didnt put enough miles on it to tell. But didnt seem to have the power in 6th either.
 

Ehmsea

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Will exhaust add hp to fix your problem - no. Sound only.
Will a tuner fix your problem - no
Your problem is the loss of mechanical advantage in going to bigger tires and aerodynamics. Gear change is your only way to get that back. Or as someone said above, forced induction.
 
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Corey6188

Corey6188

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Will exhaust add hp to fix your problem - no. Sound only.
Will a tuner fix your problem - no
Your problem is the loss of mechanical advantage in going to bigger tires and aerodynamics. Gear change is your only way to get that back. Or as someone said above, forced induction.
ok Thank you for the help.
 

MaineBumpkin

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There are 6 gears? :LOL: With the 35's on my JLUR I never even see 6th gear unless I'm going downhill over 70 Mph.
 

OldGuyNewJeep

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Hey looking to get info on maybe some solutions for my JL to hold about 75mph on the highway. I have a sport altitude unlimited 6 speed with 34 inch KO2s and 3.45 gears. Also just installed a cold air intake. Speedometer reads about 70mph when I am going 75mph but unless I am behind a large vehicle to block wind the jeep will not hold that speed in 6th gear. Barely will hold that speed in 5th gear when climbing small hills. I am in east GA by the ocean and there are no mountains and is mostly flat. Will an axle back exhaust give me any more HP or are they just sound. Also would a programmer solve the problem.
You have two choices: 1) downshift, 2) regear.

I have a Rubi with 4.10 gearing and stock 33’s. I hardly use 6th unless flat and I’m going too fast. I’m happy it’s there, though, since gearing customization might make it useful for some.
 

BuyHold

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Does anybody know how the 8-speed holds 8th gear with the 3.45s or even the 4.10s for that matter? I am wondering if this is an issue with 3.45 MT only or if it is just something that you notice more because it is a manual and shifting is on you rather than a computer.
 

Maverick909

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Hey looking to get info on maybe some solutions for my JL to hold about 75mph on the highway. I have a sport altitude unlimited 6 speed with 34 inch KO2s and 3.45 gears. Also just installed a cold air intake. Speedometer reads about 70mph when I am going 75mph but unless I am behind a large vehicle to block wind the jeep will not hold that speed in 6th gear. Barely will hold that speed in 5th gear when climbing small hills. I am in east GA by the ocean and there are no mountains and is mostly flat. Will an axle back exhaust give me any more HP or are they just sound. Also would a programmer solve the problem.
your problem is your gear ratio!! When I had my sport stock I put on rubicon take off 32.7 wild peaks and I lost my six gear unless going down hill. I added Rubi axles with 4.10’s and that changed everything! Six gear works way better then when my sport was stock.. I even just added Patagonia mt 35’s and it still allows me to use my sixth gear
 

unsavory

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I regeared my manual Rubicon from 4.10 (factory) to 4.88 after changing the tires to 34.4" BFG KO2 (aka 35s).

Made a big difference. I would go to 5.11 if I were to do it over again. Even stock with 33 inch tires, the 4.10 gear ratio was ridiculously high.

Jeep obviously geared these vehicles this high to meet emissions requirements. Which is nothing more than "green theater" since no one can drive in those gears anyway, so everyone downshifts into the gas hogging 4th gear at highway speeds. So blame your government.
 

kkarnage

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Does anybody know how the 8-speed holds 8th gear with the 3.45s or even the 4.10s for that matter? I am wondering if this is an issue with 3.45 MT only or if it is just something that you notice more because it is a manual and shifting is on you rather than a computer.
I can only speak for the 3.6 gas version, but it doesn't hold 8th much, even stock Rubis running 4:10 as standard. The moment you drop bigger tires on it without regearing, the only time you'll see 8th is on a downhill with a tailwind. That said, you don't really notice it on the 8 speed, because it's so damn slick at the gear changing. It really is a remarkably well engineered transmission, and is well matched to the new generation of 3.6 Pentastar.

As someone else already mentioned: these vehicles are geared for theoretical emissions standards. And we all know the EPA numbers are BS anyway, but the manufacturers need to make the numbers work.
 

BDinTX

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We've got a 2.0T with 8speed auto and 315/70r17 tires. I only recently started paying attention to what gear it's in on the freeway and have been noticing it spends very little time in 8th. Headwind, crosswind, slight uphill it's in 7th. I figure after the warranty expires I'll look into 4.88 gears to try and get that gear back.
 

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