Do I need to regear?

[CarbonSteel]

I have 5.13’s and with 37” KO2’s my Jeep spins exactly 2,000 RPM at 60 MPH, ideal in my opinion.

3.6L x ZF8 x 5.13 x 37 = most capable combination of those parts (especially if heavy, towing, or at altitude).

The 3.6L does not like to be lugged and lesser gearing with any of the aforementioned will result in exactly that. With a 6500 redline, even driving it like as race car, which it most certainly is not, will not even see 50% of the RPM range.

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[Gmanjeeper]

They'll run all day at 4k too, both of which are options with a simple downshift and the point of an 8spd in my opinion. The point of 2 overdrives is not to drive around at moderate loads in 8th gear though. Low load, low rpm, 8th gear, maximum efficiency. Increase in Ioad, auto downshifts up to 7 times as needed to get the necessary gearing/rpm to meet the load. I think the stock Rubicon gearing is the sweet spot at about 2350rpm at 85mph. The sahara we rented in Hawaii felt like it could use a bit more gearing with the 3.45s and 32s. Our xr felt overgeared with the 4.56s and 35s in my opinion. Granted the massive selection of gearing in the 8spd minimizes the downsides of under or overgearing. Add in the crawl ratio with the 4-1 tcase and you can pretty much run any gearing you chose until you get into the extremes on either end. That being said, as someone who tends to drive faster than most, I'd pick 4.56s for 37s and save 5.13s for 40s but they are definitely liveable on 37s especially if you don't tend to drive 80+mph.

I have a 2022 two door JLR turbo, 8 speed AT on Rubicon X take offs (BFG KO2 315 70 17s with the OEM bead lock capable wheels), 4:10 stock gearing, and a 1” spacer lift. I drive mostly around town, but 4 or 5 times a year will drive on the highway from Arkansas to Texas and, probably, once a year drive to Colorado for easy to moderate trails. I am very happy with the way it drives and, although I have only had my BFG 315s for a short period of time, I think I will average, around town, 20 mpg, give or take. With this set up, will I be able to see 8th gear at 75 - 80 mph? If not, does it matter? If I were to re gear, I would not want to go past 4:56. I will not go to 37s. Thanks.

 

[Zandcwhite]

I have a 2022 two door JLR turbo, 8 speed AT on Rubicon X take offs (BFG KO2 315 70 17s with the OEM bead lock capable wheels), 4:10 stock gearing, and a 1” spacer lift. I drive mostly around town, but 4 or 5 times a year will drive on the highway from Arkansas to Texas and, probably, once a year drive to Colorado for easy to moderate trails. I am very happy with the way it drives and, although I have only had my BFG 315s for a short period of time, I think I will average, around town, 20 mpg, give or take. With this set up, will I be able to see 8th gear at 75 - 80 mph? If not, does it matter? If I were to re gear, I would not want to go past 4:56. I will not go to 37s. Thanks.

You should still see 8th regularly in my experience. It will downshift for hills or heavy headwinds but that's nothing to worry about.

 

[Gmanjeeper]

You should still see 8th regularly in my experience. It will downshift for hills or heavy headwinds but that's nothing to worry about.

Thanks very much for your response. It is a little frustrating as info on the internet is pretty much all over the map and even different shops do not seem to agree as to whether it is necessary and, if they say it is necessary,they do not always agree as to the proper ratio. I do not mind spending the money, certainly if it would be helpful, but I do not want to go through the hassle, especially if it not make any difference or it would be something I would regret. Thanks again.

 

[grimmjeeper]

Thanks very much for your response. It is a little frustrating as info on the internet is pretty much all over the map and even different shops do not seem to agree as to whether it is necessary and, if they say it is necessary,they do not always agree as to the proper ratio. I do not mind spending the money, certainly if it would be helpful, but I do not want to go through the hassle, especially if it not make any difference or it would be something I would regret. Thanks again.

Part of it is that shops make money only when you buy something. So they have a vested interest in telling you to buy something whether you need it or not.

The bigger part of it is that the 8 speed transmission is very forgiving if your gears and tires aren't a perfect match. Back in the day the 3 and 4 speed transmissions needed a more exact ratio to perform well.

Best bet is to drive with the 315s for a while. If you think it is good enough for you, stick with it. If not, then think about regearing.

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