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New gearing???

Ghost1776

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Hi, Y'all. I'm getting ready to install a 2.5" lift on my Rubicon. I was told that 37's would fit just fine. However, I would have to regear the Jeep or it would struggle on the freeway from lack of power because of the size tire. Was I given the correct information? Or, was this person being overly cautious? Any information would be great to clear this up before I order any parts. Thank ya much.
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RodRecket

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This topic has been brought up ad nauseam. You can get by with stock 4.10s and many do, but a regear will be beneficial. Many factors play a role such as type of driving/offroading, weight of set up, and type of terrain you live in to name a few. Do a google search/search on this forum. There's a shit ton of info.
 
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Ghost1776

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Thank you. I have not built up a Jeep in about 30yrs. I'm sure some things have changed since then.
 

kevman65

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Do you have to? No.

Should you? Yes, if you spend a lot of time on the interstates/highways and especially if you have multiple elevation changes.
 

Panthers65

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Riding around on 37's and stock 4.10's will feel like you're pulling around a 2K trailer all the time.

It's also the equivalent of starting in 2nd or 3rd gear if you know how to drive a manual transmission.

Yes the Jeep will move just fine, and lots of people drive for years on larger tires and stock gears. I'd venture to guess 10% of lifted trucks and Jeeps you see on the road are regeared. While you don't know what you are missing if you never experience it, I've never heard anyone say the regret regearing a vehicle with larger tires. Most normally describe it as the best performance bang for the buck that is available.
 

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Zachanadandy

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FINAL DRIVE RATIO! Axle gears dont add power on the freeway. They might change which gear you cruise in at a given load, but the load the engine sees is determined by the final drive ratio period. The Jeep will drive no different in 8th gear with 5.13s than it does in 7th gear with 4.10s because .67x5.13=4.3 and so does .83x4.1. This 8 speed has a 4.7-1 1st gear. You don't need more gearing in 1st either. The early JK autos had a 2.86-1 and yet you still see JKs on 37s? Are they running 6.72 axle gears just to get to the same starting point as this 8 speed with 4.10s? Of course not because they don't exist. The same shops recommended the same gears for the same size tires because math is hard and running your stock gears put $0 in their pockets. You'll still see 8th gear at freeway speeds, you'll still be able to pull a trailer, the 8 speed will downshift a bit more often and that's it. A stock JLU sahara only weighs about 400lbs less than a gladiator, comes with 32" tires, and 3.45 gears. No they don't drive like they are pulling a 2k pound trailer. And yet that's the same ratio as running 4.10s and 38s... are they magic?
 

Vtur

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AT and MT tires are heavier compared to street tires in same sizes. Try it out first then decide whether to regear or not depending on your performance expectation. I decided to regear my diesel to 4.10 after just a few miles on 37s with stock gear.
 

Stan H

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FINAL DRIVE RATIO! Axle gears dont add power on the freeway. They might change which gear you cruise in at a given load, but the load the engine sees is determined by the final drive ratio period. The Jeep will drive no different in 8th gear with 5.13s than it does in 7th gear with 4.10s because .67x5.13=4.3 and so does .83x4.1. This 8 speed has a 4.7-1 1st gear. You don't need more gearing in 1st either. The early JK autos had a 2.86-1 and yet you still see JKs on 37s? Are they running 6.72 axle gears just to get to the same starting point as this 8 speed with 4.10s? Of course not because they don't exist. The same shops recommended the same gears for the same size tires because math is hard and running your stock gears put $0 in their pockets. You'll still see 8th gear at freeway speeds, you'll still be able to pull a trailer, the 8 speed will downshift a bit more often and that's it. A stock JLU sahara only weighs about 400lbs less than a gladiator, comes with 32" tires, and 3.45 gears. No they don't drive like they are pulling a 2k pound trailer. And yet that's the same ratio as running 4.10s and 38s... are they magic?
I have been running 35x12.50x17 on 4.10's for a year , I get 7th all the time and 8th at highway speeds or while cruising at 50mph + with minimal throttle. When you get on the highway the engine/transmission computer will sense the load if more torque is needed it won't go into 8th or 7th at times. So we all know that right. We'll maybe 35's is the cut off for a regear ?? Hard to say but I am completely satisfied with the performance of mine. I get all the gears everyday. I honestly dont understand why alot of people say their trucks never see 7th and 8th. Maybe it's the 37's,38's and 40's
 

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Zachanadandy

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I have been running 35x12.50x17 on 4.10's for a year , I get 7th all the time and 8th at highway speeds or while cruising at 50mph + with minimal throttle. When you get on the highway the engine/transmission computer will sense the load if more torque is needed it won't go into 8th or 7th at times. So we all know that right. We'll maybe 35's is the cut off for a regear ?? Hard to say but I am completely satisfied with the performance of mine. I get all the gears everyday. I honestly dont understand why alot of people say their trucks never see 7th and 8th. Maybe it's the 37's,38's and 40's
I've had 37s on the mojave since it had 1200 miles on it. Over 24k now. Sees 8th even in the dirt in the desert. They either have to be driving slow all the time or somehow only drive uphill?
 

Panthers65

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I've had 37s on the mojave since it had 1200 miles on it. Over 24k now. Sees 8th even in the dirt in the desert. They either have to be driving slow all the time or somehow only drive uphill?
Or people recognize performance and the importance of matching gear ratio to horsepower. Jeep could save money by putting the same ratio in every single vehicle they product, but they don't and there's a reason for that.

I'm not going down the road again, but your last statement is ridiculous. There's a reason Manufacture's' engineers place different gear ratios in different vehicles, and they have forgotten more about vehicle engineering that you or I will ever know. Match your performance mods to your driving style and what you want out of your Jeep.
 

Zachanadandy

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Or people recognize performance and the importance of matching gear ratio to horsepower. Jeep could save money by putting the same ratio in every single vehicle they product, but they don't and there's a reason for that.

I'm not going down the road again, but your last statement is ridiculous. There's a reason Manufacture's' engineers place different gear ratios in different vehicles, and they have forgotten more about vehicle engineering that you or I will ever know. Match your performance mods to your driving style and what you want out of your Jeep.
Again, the JLU sahara is effectively the same vehicle...with 3.45s. Sure if you're towing at the limit regularly you'll want to regear. If you just want to lift your rubicon and wheel it, the 4.10s work great. They wouldn't save any money by selling them all with the same gears, the gears cost them the same and I'd bet they get the axles assembled from Dana anyway.
 

Panthers65

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Again, the JLU sahara is effectively the same vehicle...with 3.45s. Sure if you're towing at the limit regularly you'll want to regear. If you just want to lift your rubicon and wheel it, the 4.10s work great. They wouldn't save any money by selling them all with the same gears, the gears cost them the same and I'd bet they get the axles assembled from Dana anyway.
Economies of Scale would say if Jeep purchased a million identical assemblies vs 250,000 of each A, B, C, and D, the million assemblies would be cheaper. Customization costs money. From the company that would make a switch to save an additional .10 per Jeep sold, if the different gear ratios weren't necessary to put out the numbers Jeep claims they wouldn't do it. Its necessary to advertise different ratings.

I didn't like my Jeep on 37's and 4.10s. It absolutely did feel like I was always pulling a trailer, and when I actually had to pull a trailer my trans temps spiked and it was miserable to keep speed or pull grade. The jeep was slower off the line, it felt like I pulled 15% of the engine power. If you're happy with 37's and 4.10's that's fine for you. I'm perfectly happy with the v6 where others think it sucks and couldn't possibly drive the gladiator without a v8 swap.
 

Stan H

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Or people recognize performance and the importance of matching gear ratio to horsepower. Jeep could save money by putting the same ratio in every single vehicle they product, but they don't and there's a reason for that.

I'm not going down the road again, but your last statement is ridiculous. There's a reason Manufacture's' engineers place different gear ratios in different vehicles, and they have forgotten more about vehicle engineering that you or I will ever know. Match your performance mods to your driving style and what you want out of your Jeep.
Well I personally think my Rubicon has plenty of power . I have pulled my big pop up and the bed of the jeep loaded down with camp gear and firewood up steep terrain dirt road even and it does fine.
Let me ask a question just how high of a gear do you want while ypur towing 3000 pounds up a steep dirt road ? 6th, 7th ,8th.. I will tell you what I think I think everyone just has different views of performance and power and how fast they want to go or how high of a gear they think they need to pull a load in
. Cheers.
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