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488s or 456s. That is the question

Gremlinsteve

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It’s down to the wire. I want 488 gearing. Just not sure I need them

The Jeep is the automatic eight speed version on 35/12.50s

I do light towing on occasion and will be on light trails

If you have either of these gears can you give me real world data
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Tufelhundin

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your wording of "light" used for both scenarios would lead me to suggest 4.56 only because this is what I did and Im happy with them. Im not here to promote the 4.56 because "I have them so they must be the right gearing", but I do believe that having 4.56 and 35's your end gearing should be very close to the same as a stock Max tow...just a little more geared.

I had 3.73's on 35's and never saw 8th and it would go in 7th only in the perfect conditions...tail wind or down hill. Spent pretty much all its time in 6th.

I can now be in 8th with the cruise set at 45mph and believe it or not I can slow roll it like a diesel and it will actually accelerate from that speed in 8th.


**another reason I went to 4.56 is because 35's is the max size I plan to use.



Are 4.88's better? I have no idea, but the only way I would have chose them is if I was possibly thinking of going to 37's. Just my 2 pennies anyway.
 

DocMike

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Gonna restart this. I am at altitude. I have heavy ass Black Rhino Rims on 35s

Was leaning 4.88. My friends with 37s have 5.13 out here and love it.
Now.... Northridge sells:


https://www.northridge4x4.com/part/...-4-88-front-ring-and-pinion-set-w-d44-upgrade

Front and rear. Would be a bit over $700.

They also sell this:
https://www.northridge4x4.com/part/...e-d44-front-and-rear-ring-and-pinion-kit-4-88

Do I need all this extra stuff? I have 15K on my Jeep.

Finally.... Warranty wise. Should I get Jeep to re flash or install? I mean I can set the new gearing with the Tazer, but then I have to remove the Tazer for dealer visits.

I can't imagine the shenanigans that will happen if I go from 3.73 to 4.88 and pull the taser for the drive to Jeep.
 
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Gremlinsteve

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I chose 35s and 4.88s
It’s my understanding a dealer won’t flash the pcm any longer

I also used a reputable shop and let them source the gear. I figure if there is an issue it’s easier to get them to fix it that way

At 15k I’m sure any shop would want you to replace the bearings for the carrier ect

Mine only has a few hundred miles on it and there not doing it as far as I know
 

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rharr

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You should use http://www.grimmjeeper.com/gears.html to calculate out the ratio that gets you as close to stock for the rpm per speed.

as you increase tire size your rpms go down and your speed goes up, thus requiring the engine to work harder.

You regear to get back closer to stock rpm/speed assuming the manufacturer designed optimal engine performance at a certain rpm and speed.

If you are towing heavy you regear to have the engine's optimal performance come on sooner (700 extra rpms at 55mph over stock), higher rpms, slower speed, the high rpms is where a gas motor builds power.

Generally you don't want to over gear by much more then 500 to 700 rpm at say 55mph. Otherwise you are just revving the motor out for no reason burning gas.

plug in all the stock jeep info into the above site, including stock tires, then do a compare calc by only changing tire size, then go to the bottom page and see how much your rpms dropped per a common speed. then go and play with axle ratios until you get the tables at the bottom to match closely.
 

FLUndertaker

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Plenty of data on this site already about this topic. Survey says:

4.56 for 35s
4.88 for 37s
how many folks have you ever heard say they wish they hadnt gone so deep on their regear?

Survey Says:

None

4.88 for 35”
5.13 for 37”

love my 5.13 with pedal commander. No regrets whatsoever. So thankful I didn’t play it safe and go with 4.88. Acceleration is outstanding, gotta be careful to not spin the tires. Highway cruise is easy 8th gear with plenty of passing power. MPG is who knows, I didn’t buy a brick shaped vehicle and expect to get good fuel economy.
 

rharr

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@DocMike
you should get the full kit with bearings. The pinion will likely need a bearing at least plus the shims will be needed to align the ring and pinion to each other. If you are not doing the work yourself just have the axle shop you select order the gears and kit.

Generally speaking shops have preferred manufactures/parts they like to use, them ordering the parts gives them a consistency that prevents return warranty work caused by a crappy part that failed and now the shop has to eat the labor cost to redo the work. Yukon Gear is a known good manufacturer.
 

DocMike

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Good info to have. Northridge Denver is closed for good. Not sure about shops in the springs.
Heard lots of bad about Predator from people in the know.


@DocMike
you should get the full kit with bearings. The pinion will likely need a bearing at least plus the shims will be needed to align the ring and pinion to each other. If you are not doing the work yourself just have the axle shop you select order the gears and kit.

Generally speaking shops have preferred manufactures/parts they like to use, them ordering the parts gives them a consistency that prevents return warranty work caused by a crappy part that failed and now the shop has to eat the labor cost to redo the work. Yukon Gear is a known good manufacturer.
 

rharr

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WK2JT

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how many folks have you ever heard say they wish they hadnt gone so deep on their regear?

Survey Says:

None

4.88 for 35”
5.13 for 37”

love my 5.13 with pedal commander. No regrets whatsoever. So thankful I didn’t play it safe and go with 4.88. Acceleration is outstanding, gotta be careful to not spin the tires. Highway cruise is easy 8th gear with plenty of passing power. MPG is who knows, I didn’t buy a brick shaped vehicle and expect to get good fuel economy.
Go as deep as possible… let the wildly inappropriate comments begin!
 

spectre6000

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Well... Jeep themselves have pretty well spoken on the topic when they announced the 35" tires on the Recon (or whatever it's called) package trotted out to throw water on Ford's Bronco fire. 4.56 is the standard, but you can option up to 4.88. Exercising that option gets you a 100:1 crawl ratio with the manual.

The question I have about that is whether or not the 4.88 is in any way necessary for 35"s, or if it's purely for the bragging rights (I'm leaning in the latter direction). That said, the JT can do bigger, heavier things, so the 4.88 may make a bit more sense beyond just the crawl ratio number on paper... The above combined with the knowledge that the lower trims come stock with 3.88 or something (I forget, less than the optional 4.10) without any loss of capacity makes me lean in the 4.56 direction. Spinning the engine faster isn't necessarily better, and is likely worse from the perspective of longevity.

Then you mention you're at altitude. Me too. Home base is at 7K', and you know how it goes with everything being some manner of up or down hill, air density losses, etc. I'd still go with the 4.56.
 

DocMike

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Home is about 6,300. The only time the 3.73 felt right was with the Sport S tires. Even then.....
I have had a few trails where I was on a short climb and had to floor it with 33s and felt like I was going to stall. I'd like to do it once and do it right. I wonder what a roof top tent etc would impact or a camper? Will I got to a 37? Probably not. It would take a lot of extra work to do it right, Will I look at @FR33DOM and see his 37s and drool. yes. HE does love his 5:13.


Well... Jeep themselves have pretty well spoken on the topic when they announced the 35" tires on the Recon (or whatever it's called) package trotted out to throw water on Ford's Bronco fire. 4.56 is the standard, but you can option up to 4.88. Exercising that option gets you a 100:1 crawl ratio with the manual.

The question I have about that is whether or not the 4.88 is in any way necessary for 35"s, or if it's purely for the bragging rights (I'm leaning in the latter direction). That said, the JT can do bigger, heavier things, so the 4.88 may make a bit more sense beyond just the crawl ratio number on paper... The above combined with the knowledge that the lower trims come stock with 3.88 or something (I forget, less than the optional 4.10) without any loss of capacity makes me lean in the 4.56 direction. Spinning the engine faster isn't necessarily better, and is likely worse from the perspective of longevity.

Then you mention you're at altitude. Me too. Home base is at 7K', and you know how it goes with everything being some manner of up or down hill, air density losses, etc. I'd still go with the 4.56.
 

spectre6000

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A RTT would only affect things at speed. It doesn't weigh much, just frontal area and drag. Not sure what you mean by "camper". There are a number of colloquial meanings. A topper? Camping trailer? Something else? Topper won't affect much, trailer might.

Rubicons, Mojaves, and Max Tows have 4.10, and I recall seeing a chart not long ago that had RPM on one axis, tire size on another, and R&P at the intersections. Too low or too high were colored somehow to warn away, and there was a range of happiness. 35" tires had a happiness range of 4.10, 4.56, and 4.88. Looking at other ratios and tire sizes that Jeep is known to have used stock, the 4.10 with 35"s corresponded with the stock ratio on the lesser trims. Essentially by their logic, it's the fuel economy oriented choice. If you didn't care for the stock on stock in a non-Rubicon/Mojave/Max Tow, you'll be similarly unhappy with 4.10s on 35s (though you'll not lose your capacities). Accordingly, 4.56 would be your "all rounder", and 4.88 would be for power.

Another meaningful datapoint might be that being able to bolt on 35"s was a design parameter. They assume different trims are to be used differently, and the Rubicon trim is the one most likely to be used that way. 4.10 should work according to that design parameter, but there's always that "how well" element.

When I eventually get my truck (a Rubicon), I'll be putting 35s on it. I'll give the 4.10s a shot, and expect to be happy with them. I've DDd a number of cars over the years with double digit horsepower, and don't drive very fast in trucks (there are other cars for that). If it can't do what I need it to do as a truck, I'll reassess gearing, but otherwise I'll take it easy and enjoy the fuel savings.
 

WK2JT

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37’s with 5.13’s and soooo regretting I didn’t go 5.38’s. MPG actually got better with the 5.13’s over the stock 3.73’s and it’s just getting into the sweet spot power wise when cruising 70ish. Jeep has to make compromises for various regulations, blah, blah, blah… you don’t when you modify. Regearing is not a linear exercise because of additional rotational mass and leverage acting against you with a larger tire radius. Also, RPM’s weren’t even optimal when stock so that shouldn’t be your measuring stick in my opinion. I went for drivability and the 5.13’s w/ 37’s are nice, but I’ve also driven one with 5.38’s and it was even a little better… wish I wouldn’t have driven it now.
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