4.88, 4.56, or 4.1 gears for 285 75 17

TyRoosevelt

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Hello everyone,

I put on some 285 75 17 Toyo AT3s and I am not quite happy with the performance. I am definitely not getting 8th and I recalibrated with jscan. The actual tire size is 32.75 high and I am a little surprised it is not hitting 8th since my willys tires were pretty tall themselves.

Essentially, will the shift points eventually get better or do I need to regear?

I have called 3 shops and each one of them recommended either 4.1, 4.56, or 4.88.

Which one should I go with? Is the regear worth it? How does it impact performance compared to stock? Better? Smoother?

I don't want to spend the money unless it actually has substantial benefits. Are there any negatives to the regear? Any thoughts would be appreciated.
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Imo- Of you dont plan on going any bigger, 4.33. 4.56 if you plan to tow. If youre going to 35’s; 4.56 or 4.88 respectively.

but yes. Regearing is a big benefit. My jeep came with those tires and 4.1, and i would have regeared it even if I hadnt gone to 37’s.
 
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TyRoosevelt

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Imo- Of you dont plan on going any bigger, 4.33. 4.56 if you plan to tow. If youre going to 35’s; 4.56 or 4.88 respectively.

but yes. Regearing is a big benefit. My jeep came with those tires and 4.1, and i would have regeared it even if I hadnt gone to 37’s.
I guess I am confused about what are the benefits? Is it faster? Does it shift smoother? Does it drive better than stock? Thanks
 

Whaler27

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Hello everyone,

I put on some 285 75 17 Toyo AT3s and I am not quite happy with the performance. I am definitely not getting 8th and I recalibrated with jscan. The actual tire size is 32.75 high and I am a little surprised it is not hitting 8th since my willys tires were pretty tall themselves.

Essentially, will the shift points eventually get better or do I need to regear?

I have called 3 shops and each one of them recommended either 4.1, 4.56, or 4.88.

Which one should I go with? Is the regear worth it? How does it impact performance compared to stock? Better? Smoother?

I don't want to spend the money unless it actually has substantial benefits. Are there any negatives to the regear? Any thoughts would be appreciated.
I’m surprised.

I wouldn’t regear.

I have a Rubicon, so it came with 410s. It performed great with true 34s, and it still drives well with fake 37s now (37” BFG KO2s, which are really about 35.5”). If I was feeling rich, and I’d already bought new Alcon brakes, I’d probable install 456s now. They’d be better, but they really aren’t necessary. My brother feels the same way. (I have the 6 & he has the 4, and we’re both running the same tires.) Unless you plan on going taller than a true 34“ tire, the 410s are plenty-plenty. You can tow more than I’d ever want to tow with a wrangler with that set up (terrible tow vehicles).

I had 456 gearing in my last TJ with 33” tires, and it was just right, but I had a six speed and the old 6 was gutless by comparison. My JL with 37s and stock 410 gearing lugs along nicely, and it climbs, crawls, and jumps off the line better than the TJ did with 456 gearing. 488s would be overkill for 33s on a JL. And a bad plan unless you live off road and never drive on the highway.
 
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TyRoosevelt

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I’m surprised.

I wouldn’t regear.

I have a Rubicon, so it came with 410s. It performed great with true 34s, and it still drives well with fake 37s now (37” BFG KO2s, which are really about 35.5”). If I was feeling rich, and I’d already bought new Alcon brakes, I’d probable install 456s now. They’d be better, but they really aren’t necessary. My brother feels the same way. (I have the 6 & he has the 4, and we’re both running the same tires.) Unless you plan on going taller than a true 34“ tire, the 410s are plenty-plenty. You can tow more than I’d ever want to tow with a wrangler with that set up (terrible tow vehicles).

I had 456 gearing in my last TJ with 33” tires, and it was just right, but I had a six speed and the old 6 was gutless by comparison. My JL with 37s and stock 410 gearing lugs along nicely, and it climbs, crawls, and jumps off the line better than the TJ did with 456 gearing. 488s would be overkill for 33s on a JL. And a bad plan unless you live off road and never drive on the highway.
Maybe I didn't mention it but I have the 3.45. My tires are only 61 lbs as well. I don't get it. That's why I was hoping the shift points would adjust. I don't know how long that takes though.

Others have said they haven't had a problem. I guess is not running 8th not a problem?

37s on your 4.1 should run similar to my 34s on a 3.45. Are you running 8th gear?

I wonder if anything over a 4.1 is overkill. I am getting over 21 mpg so if the only benefit is 8th, is it even worth it?
 

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I guess I am confused about what are the benefits? Is it faster? Does it shift smoother? Does it drive better than stock? Thanks
its faster because of the tq multiplication effect of the gearing

the transmission doesnt have to work as hard vis a vis leas shifting

youll generally get better mileage on account of not having to load the engine as much and down shift as much.
 

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Lower gears are quicker, and can improve mpg around town. Taller gears are faster and can improve mpg on the freeway. Your current setup would only be turning 1,371 rpm at 60mph in 8th gear, at 80mph it would be turning 1,828 rpm. If you don't do much freeway driving and/or never drive over 65mph re-gearing could benefit you. Our jlur on 37's is turning 1,499 at 60 and 1,996 at 80 on the factory 4.10's which is about perfect for us as we do a lot of roadtrips in the western states where freeway speed limits are generally between 70-80mph. Coming back from moab I had the cruise control set at 85, held 8th no problem, and got 14 mpg average. It would have been worse with lower gears. The beauty of our 8 speed autos is they have so many gears we have much more leeway in gearing choice. In a TJ or early JK where the auto had a ~2.8 to 1 1st gear you had to go low on axle gears to be drivable. Our 4.7 to 1 1st gear makes almost any axle gearing doable. Gone are the days of having to gear so low in a lifted jeep that you couldn't drive over 65mph because the engine was screaming. Our 8th gear over drive is so tall that you can choose deep axle gears and still maintain freeway speed. With this trans it truly is personal preference.
 

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Lower gears are quicker, and can improve mpg around town. Taller gears are faster and can improve mpg on the freeway. Your current setup would only be turning 1,371 rpm at 60mph in 8th gear, at 80mph it would be turning 1,828 rpm. If you don't do much freeway driving and/or never drive over 65mph re-gearing could benefit you. Our jlur on 37's is turning 1,499 at 60 and 1,996 at 80 on the factory 4.10's which is about perfect for us as we do a lot of roadtrips in the western states where freeway speed limits are generally between 70-80mph. Coming back from moab I had the cruise control set at 85, held 8th no problem, and got 14 mpg average. It would have been worse with lower gears. The beauty of our 8 speed autos is they have so many gears we have much more leeway in gearing choice. In a TJ or early JK where the auto had a ~2.8 to 1 1st gear you had to go low on axle gears to be drivable. Our 4.7 to 1 1st gear makes almost any axle gearing doable. Gone are the days of having to gear so low in a lifted jeep that you couldn't drive over 65mph because the engine was screaming. Our 8th gear over drive is so tall that you can choose deep axle gears and still maintain freeway speed. With this trans it truly is personal preference.
That’s interesting to me that your 4.10 gears hold 8th going 80 mph with 37’s. I wonder if there is something wrong with my Jeep since on my 3.45 gears and stock 245/75 r17 wheels it always drops to 7th going 80 mph. I loose 8th gear right about 77mph. That’s going across Nebraska on I-80 so really flat ha!
 

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I think you should look at the cost of regearing and then ask yourself if you’re not happy with the way your Jeep drives. That’s the bottom line.

Having an 8th gear you use infrequently is like having an overdrive you use infrequently... it’s in the who cares department. If you’re not happy with the amount of grunt you have down low, and the cost is no big deal, 410s would be great. Gearing lower than that would be a mistake unless you’re considering much taller tires.
 

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I think you should look at the cost of regearing and then ask yourself if you’re not happy with the way your Jeep drives. That’s the bottom line.

Having an 8th gear you use infrequently is like having an overdrive you use infrequently... it’s in the who cares department. If you’re not happy with the amount of grunt you have down low, and the cost is no big deal, 410s would be great. Gearing lower than that would be a mistake unless you’re considering much taller tires.
I’m considering a regear as well. 2.0 with 3.45’s and plan to run 34’s, never more than a 35 because I will need new axles eventually and that is a bridge too far. I’m thinking 4.10 gears because I drive a lot of highway and it seems like the jump to 456 would be excessive. I also plan to stick with Spicer parts. The Advantek rear diff, the factory gears have some special attributes apparently to help efficiency. Shrug
 
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Whaler27

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I’m considering a regear as well. 2.0 with 3.45’s and plan to run 34’s, never more than a 35 because I will need new axles eventually and that is a bridge too far. I’m thinking for 10 years because I drive a lot of highway and it seems like the jump to 456 would be excessive. I also plan to stick with Spicer parts. The Advantek rear diff, the factory gears have some special attributes apparently to help efficiency. Shrug
410s are the perfect balance for the scenario you describe.

The fact that there are shops out there that will recommend 488s for a JL running 32.75” tires and wanting highway drivability proves, again, that many people in the business give awfully lousy advice.
 

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I’ve regeared a couple of vehicles before of the performance variety. Too much gear is worse than not enough....1000%. It sucks the fun out a perfectly good vehicle and makes it an utter nuisance.
 
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TyRoosevelt

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I’ve regeared a couple of vehicles before of the performance variety. Too much gear is worse than not enough....1000%. It sucks the fun out a perfectly good vehicle and makes it an utter nuisance.
That is what I have been worried about. Each shop is giving me different advice and different prices. I had a 4.88 on my JK and I hated it. I am trying to avoid that.

Starting to wonder if I should just forget about 8th gear.

Anyone near the Denver area that can recommend a good shop with a good price? One shop told me $4000 and then 4 wheel parts told me $1700. Crazy that there is such a huge discrepancy.
 

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That is what I have been worried about. Each shop is giving me different advice and different prices. I had a 4.88 on my JK and I hated it. I am trying to avoid that.

Starting to wonder if I should just forget about 8th gear.

Anyone near the Denver area that can recommend a good shop with a good price? One shop told me $4000 and then 4 wheel parts told me $1700. Crazy that there is such a huge discrepancy.
Not in the Denver area, but typically the going rate is $800-1,000 per axle. If I were dropping the money on gears, I'd save a little more and add lockers. Easier in my mind to justify the expenditure when it's a massive improvement in off road capability and a slight improvement in driveability. I think the extra ~200 rpms makes all the difference in holding 8th, but our 7th gear is an over drive as well. Not holding 8th wouldn't be enough of a reason to drop $2k in my opinion.
 
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TyRoosevelt

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Not in the Denver area, but typically the going rate is $800-1,000 per axle. If I were dropping the money on gears, I'd save a little more and add lockers. Easier in my mind to justify the expenditure when it's a massive improvement in off road capability and a slight improvement in driveability. I think the extra ~200 rpms makes all the difference in holding 8th, but our 7th gear is an over drive as well. Not holding 8th wouldn't be enough of a reason to drop $2k in my opinion.
That's been my dilemma. And here is the thing, I held 8th without doing anything for a over 5 minutes after I first calibrated it. Then I haven't seen it since.

Any brand for gears that you guys like? One shop said I could choose whatever brand I wanted.
 
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