Ordered a 2023 Rubicon 392 today

Most fun you’ll have with your clothes on! The Mopar engineers knew this was the V8 swan song and they did things that make no sense except that it’s just fun.
 
I'm new to this site but not new to the off road world. I ordered my 392 last month and can’t wait to do a monster build on it. I've seen quite a few nice rigs on this site and really like some of the ideas people have. I like to look around at you all's rigs to get ideas of do's and don'ts for when my time comes but occasionally someone says something that just makes me feel I need to help out.

@JC, my reply is by no means meant to dog you but maybe open your eyes and help others in their Jeep builds. It’s great that you can "squawk" your tires from a dead stop, XR or non-XR, these are some pretty bad ass Jeeps but there is way more factors involved in having a dialed in Jeep. The correct gearing for your vehicle is super important for the performance and engine/tranny life. These drive trains, especially new vehicles, are so engineered and tuned in for fuel economy, emissions and power. The engine is engineered and tuned to run its best during what’s called a "standard day" condition, meaning that the engine preforms better at set veritable’s during standard day conditions and those are sea level, barometric pressure @ 29.92 and temperature @52F.

Now, match that engineering (the 392 was engineered by the old Viper crew) with the rest of the drive train and configure the vehicle (gears and tire size) to operate at its optimum range, usually @ 65mph or 70mph and the correct engine RPM’s. This will ensure the engine is operating at its correct operating temperature, power range, fuel delivery and emissions output and the easiest way is through the gear set. There are several graphs out there that show what your gearing should be using your tire size and RPM range. The graph will show you what gearing is best for you, if you want better mileage, more power or a balance of power and fuel economy. The best gearing choice is one that’s close to your stock configuration. Having an engine powerful enough to light up 37” tires while running 3.73 gears is awesome but is NOT optimal and putting massive stress on the power train which will catch up with you sooner or later. Now 3.73 gears with 33” tires would put your RPM’s around 2207 to 2470, that gearing is more for fuel economy/balanced power but not near high power range setting and is great for the engine and tranny. But go even further with the same gears running a 37” tire and you’re looking for trouble.

So someone ordering a 392 with the XR package (4.56 gears) and going to run a 37” tire is right one the money. Personally, I feel its well worth the extra $4k just for the gear set alone. Swapping gears usually runs the average person $2k per axle anyway and they don’t have the added cost of buying a different Carrier to go from 3.73’s to 4.56 ring and pinions. But if someone is NOT going to run a tire larger then 33”, the non-XR is the way to go.

Sorry for the long reply but your Jeep is going to treat you the way you set it up.
Not her to debate gear ratios, the best is determined by what you want to use your Jeep for, 3.73 right for some and 4.88 right for others. However your RPM estimate is way off, in the 392 with the 8-speed and 3.73s your only about 2100 at 80mph. If I spent more time at 65 I could tell you the exact RPM, it‘ll be much lower of course but that path is only crossed momentarily on excel or decel.
 
You couldn't pay me to run 4.56 gears in this Jeep.
Like I said before it`s all up to what you intend to do with your Jeep, if your thinking about gas mileage get a 4XE.
I have always owned Rubicons and have a 18 that I had put a Ripp supercharger on before E torque was available, that Jeep had 3:73 gears in it and without the supercharger it was a dog with the 3:73 gears, it took the supercharger to make it right with 35" tires.
My first 392 had the 3:73 gears and with the 33"`s it was okay but after putting 35"`s on it you could tell the difference in performance
The 392 XR came with the stock 35" tires and it was a fine combination but after putting 37"`s on it you could feel that it still had the same performance and pulled along nicely. If you look at gearing charts you will see what the optimum gearing for your tire size is and the 4:56 gears are perfect for the 37`s and actually you could go to a taller tire and still be in the right gearing range.
If you don`t want to smoke the tires don`t get on it so hard and as far as the mileage goes I could not notice a difference in my low MPG. It all boils down to what you are looking to do with your Jeep?
All of this is my personal opinion based on owning and working on Jeeps for 40 years.
Gearing charts don`t lie but you can still run what ever you want. I was at the Jeep Invasion in Wildwood NJ this summer and I can tell you I had seen Jeeps (Sport) with 3:23 gears running 37" tires and even 40" tires with 3:73 or 4:10 gears with there being 2500 Jeeps there you could see just about any combination possible
Just my 2 cents


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