Tire Sizes & Gear Ratios

CarbonSteel

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Like many of you, I have started playing with adding larger tires and lower gears. Using @AnnDee4444's awesome gearing calculator, I can see that 4.88 gears and 37" tires will be about the same (more or less) as the OEM 4.10 gears and 33" tires.

I am leaning really hard towards 35" tires because the 4.88 gears will give me a little more response and torque, but then I am wondering what a 2.5" MC GC lift will look like with 35" tires.

Opinions welcome (help me with my paralysis by analysis)

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CarbonSteel

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oldcjguy

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Like many of you, I have started playing with adding larger tires and lower gears. Using @AnnDee4444's awesome gearing calculator, I can see that 4.88 gears and 37" tires will be about the same (more or less) as the OEM 4.10 gears and 33" tires.

I am leaning really hard towards 35" tires because the 4.88 gears will give me a little more response and torque, but then I am wondering what a 2.5" MC GC lift will look like with 35" tires.

Opinions welcome (help me with my paralysis by analysis)
Stick or auto? 3.6 or 2.0T? Daily driver? What kind of off-roading do you do? More sand, more mud, more rock crawling?
 

mskillen

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It had the Milestar Patagonias on it, now it has the Falken Wildpeak AT3's for the winter.
The Falkens are very nice tires I like them so far, I'm going wheelin next weekend so I will be able to see the difference on the trail between the MT and the AT
The milestars were worn out in about 18000 miles, I wont get them again.
I'm looking at trying the Yokohama Geolander MT G003 in 37s next.
Wheels are KMC XD231 RG's
 
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CarbonSteel

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Stick or auto? 3.6 or 2.0T? Daily driver? What kind of off-roading do you do? More sand, more mud, more rock crawling?
3.6/Auto/Daily Driver. Offroading includes mostly sand, but some rocks. Really just getting into rocks, but more from a trail perspective like Red Cone in CO.
 

oldcjguy

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3.6/Auto/Daily Driver. Offroading includes mostly sand, but some rocks. Really just getting into rocks, but more from a trail perspective like Red Cone in CO.
With 35s and the auto I'd stick with the 4.10 for now. Between the advantage of having a torque converter and the gear ranges in the auto I think you're in good shape with 35. Especially as a daily driver. Personally I think the 4.88 are a bit too much for a 35, and our 8 speed is different world. It's a lot different than the jk days with the 5 spd auto. On the plus side it keeps your axles under warranty. If you go up to 37s maybe change to 4.88 then.

Since you have a rubi you already have the extra craw 4:1 gearing of rubi's transfer case in 4lo vs 2.72 in a non-rubi. Your final drive in 4lo is still lower (numerically higher) than a non-rubi with 5.13s even. So the rocks shouldn't be an issue for you at all.

Have you considered a tuner like a SuperChips? That could put some pep and throttle response in your jeep. A lot of the time that missing response and torque is actually the computer doing "torque management" and not giving you what you ask for when you ask for it. Just because you floor it doesn't mean the computer gives you full throttle. Drivability on tuned jeeps goes way up. Bonus... you'd be able to adjust for tire size and gear changes any time you wanted.

I'd try keeping the 4.10 and 35s with a tune and see how you like it. You can always gear later.

I'm going to be doing tires and a lift too. My Jeep is still new and I'm waiting to put some miles on it first and get the steering tsb done. Make sure there are no issues. I have the 2.0T and plan on doing 35s, a lift, and a tune. I'm keeping the 4.10s. I drove a lifted 2.0T JLUR with 35s and big heavy 20" or 22" rims (I forget which) with a SuperChips tune in it. That jeep felt much peppier than my JLUR with stock rims and tires and it had no gearing changes.
 
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With 35s and the auto I'd stick with the 4.10 for now. Between the advantage of having a torque converter and the gear ranges in the auto I think you're in good shape with 35. Especially as a daily driver. Personally I think the 4.88 are a bit too much for a 35, and our 8 speed is different world. It's a lot different than the jk days with the 5 spd auto. On the plus side it keeps your axles under warranty. If you go up to 37s maybe change to 4.88 then.

Since you have a rubi you already have the extra craw 4:1 gearing of rubi's transfer case in 4lo vs 2.72 in a non-rubi. Your final drive in 4lo is still lower (numerically higher) than a non-rubi with 5.13s even. So the rocks shouldn't be an issue for you at all.

Have you considered a tuner like a SuperChips? That could put some pep and throttle response in your jeep. A lot of the time that missing response and torque is actually the computer doing "torque management" and not giving you what you ask for when you ask for it. Just because you floor it doesn't mean the computer gives you full throttle. Drivability on tuned jeeps goes way up. Bonus... you'd be able to adjust for tire size and gear changes any time you wanted.

I'd try keeping the 4.10 and 35s with a tune and see how you like it. You can always gear later.

I'm going to be doing tires and a lift too. My Jeep is still new and I'm waiting to put some miles on it first and get the steering tsb done. Make sure there are no issues. I have the 2.0T and plan on doing 35s, a lift, and a tune. I'm keeping the 4.10s. I drove a lifted 2.0T JLUR with 35s and big heavy 20" or 22" rims (I forget which) with a SuperChips tune in it. That jeep felt much peppier than my JLUR with stock rims and tires and it had no gearing changes.
Super chips do not "write" to the ECM such that FCA can those programming edits if I take it in for repairs?
 

oldcjguy

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Super chips do not "write" to the ECM such that FCA can those programming edits if I take it in for repairs?
You can return it to stock, so the factory tune is in there when you bring it in for service. If they plug in their tools it reports stock. Technically, if they removed your ecm and sent it somewhere to be analyzed they could tell. Never heard of anyone doing that, but I'm sure it's technically possible. Dealerships do not have the tools to be able to tell though. Any of the companies that unlock the ecm for non-jeep tunes needs to make changes to the ecm to allow it to be custom programmed. I guess you could buy a second pcm and keep your stock one unmodified. I don't think dealerships worry about that with jeeps. I think they worry about Mustangs, Corvettes, and Challengers etc... being tuned. Now if they open your hood and see replaced bolts or new gaskets, or signs of nitrous plumbing, or it looks like you swapped out the turbo for a big turbo and put it all back to stock after blowing the motor, that might raise an eyebrow.

But it that's a concern then don't do it.

My last car was a hellcat and I modified it. Honestly, if something went wrong with the engine I could have loaded a stock tune back in it and returned it back to stock, but at that point I wouldn't. If I broke something that's on me. but I never did, it ran great and whoever bought it from the dealer I traded it in to got a great car. I never removed the tune when bringing it in for service and they never said anything either. I'm not worried about a 93 octane Jeep tune that comes from SuperChips. Those companies do their homework and know how to tune. It's their reputation on the line. I'm not hunting for peak power or worried about really overstressing parts in a jeep I'm looking for improved drivability on and off road. I'm just more of a fan of the handheld tuner. I think they get finer control to do things correctly and better.

If you're concerned about it, there are inline units. A device that sits between the ecm and the engine. Edge makes a Pulsar that just bolts to the factory ecm. If you need to take it in for service you can remove it. They can't give you as much as an actual tune, but they can make a noticeable difference. There's probably some threads on here about people who have used them. Maybe check them out?
 
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You can return it to stock, so the factory tune is in there when you bring it in for service. If they plug in their tools it reports stock. Technically, if they removed your ecm and sent it somewhere to be analyzed they could tell. Never heard of anyone doing that, but I'm sure it's technically possible. Dealerships do not have the tools to be able to tell though. Any of the companies that unlock the ecm for non-jeep tunes needs to make changes to the ecm to allow it to be custom programmed. I guess you could buy a second pcm and keep your stock one unmodified. I don't think dealerships worry about that with jeeps. I think they worry about Mustangs, Corvettes, and Challengers etc... being tuned. Now if they open your hood and see replaced bolts or new gaskets, or signs of nitrous plumbing, or it looks like you swapped out the turbo for a big turbo and put it all back to stock after blowing the motor, that might raise an eyebrow.

My last car was a hellcat and I modified it. Honestly, if something went wrong with the engine I could have loaded a stock tune back in it and returned it back to stock, but at that point I wouldn't. If I broke something that's on me. but I never did, it ran great and whoever bought it from the dealer I traded it in to got a great car. I never removed the tune when bringing it in for service and they never said anything either. I'm not worried about a 93 octane Jeep tune that comes from SuperChips. Those companies do their homework. It's their reputation on the line. I'm not hunting for peak power or worried about really overstressing parts. I'm just more of a fan of the handheld tuner. I think they get finer control to do things correctly and better.

If you're concerned about it, there are inline units. A device that sits between the ecm and the engine. Edge makes a Pulsar that just bolts to the factory ecm. If you need to take it in for service you can remove it. They can't give you as much as an actual tune, but they can make a noticeable difference. There's probably some threads on here about people who have used them. Maybe check them out?
I could have sworn that I read the ECM was also encrypted (or perhaps part of it)? I see for Livernois you have to send the ECM to them to have it unlocked. For me that is a non-starter, because I am sure that FCA can detect that and void your warranty.

I will continue to ponder about the re-gear and I think after MC GC lift is installed, I will have a better idea of which tire size I want, which will then dictate any gear changes.
 

oldcjguy

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I could have sworn that I read the ECM was also encrypted (or perhaps part of it)? I see for Livernois you have to send the ECM to them to have it unlocked. For me that is a non-starter, because I am sure that FCA can detect that and void your warranty.

I will continue to ponder about the re-gear and I think after MC GC lift is installed, I will have a better idea of which tire size I want, which will then dictate any gear changes.
Yup with all of the companies you must send in your ecm. You may want to consider an inline module.

Keep in mind the lift and gear changes are going to void portions of your warranty too. I'd try the tires without the gears first. Why void the warranty on your axles if you don't need to?
 
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CarbonSteel

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Yup with all of the companies you must send in your ecm. You may want to consider an inline module.

Keep in mind the lift and gear changes are going to void portions of your warranty too. I'd try the tires without the gears first. Why void the warranty on your axles if you don't need to?
Honestly, there is not much to an axle versus the electronics of the vehicle. Re-gearing replaces all but a few bearings and not that it would make any difference, but I would use Dana/Spicer parts in the re-gear. Losing the warranty on the axle is not really a concern versus losing it on the electronic systems, but I like your thinking! :clap:

I have less paralysis now.
 

oldcjguy

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Honestly, there is not much to an axle versus the electronics of the vehicle. Re-gearing replaces all but a few bearings and not that it would make any difference, but I would use Dana/Spicer parts in the re-gear. Losing the warranty on the axle is not really a concern versus losing it on the electronic systems, but I like your thinking! :clap:

I have less paralysis now.
The locker position sensor in the axles is not a replaceable part. If it goes bad the dealer will replace the entire axle assembly. If you're not under warranty the bill is on you. At that point you could replace the locker with an aftermarket unit or use one of those wiring fixes to mask it and manually control the lockers. Super dumb that the sensor can not be replaced, but plenty of threads on it. Something to think about. That's one reason I'd consider not changing gears right away.
 
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CarbonSteel

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The locker position sensor in the axles is not a replaceable part. If it goes bad the dealer will replace the entire axle assembly. If you're not under warranty the bill is on you. At that point you could replace the locker with an aftermarket unit or use one of those wiring fixes to mask it and manually control the lockers. Super dumb that the sensor can not be replaced, but plenty of threads on it. Something to think about. That's one reason I'd consider not changing gears right away.
Yep; typical OEM that does not sell the part separately which only costs them a buttload in the end by replacing the entire axle assembly. I see some chatter about the part becoming available separately so that would be nice. I also see that @chevymitchell has a "how to guide" on how to pot the PCM within the sensor to prevent oil from entering. I thought that it was a strange setup when I initially dumped the oil in mine at 5K. Electronic sensors submerged in oil--what could possibly go wrong with that?

Z Automotive also has a fix:

https://www.zautomotive.com/product/z-locker-oem/
 

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