31's with 4.56 gears???

I have 31'' BFG MT's on my jeep and plan on going bigger but I still have alot of tread on them. This is my DD so there is about 60-70 miles a day put on her, over half of it being highway miles. I dont want to gear to 4.10 then regear to 4.56 after. Anyone run this setup? How high does the rpm's get on the interstate? By the way I have an auto tranny in it. Thanks for any help.

rkates said:

I have 31'' BFG MT's on my jeep and plan on going bigger but I still have alot of tread on them. This is my DD so there is about 60-70 miles a day put on her, over half of it being highway miles. I dont want to gear to 4.10 then regear to 4.56 after. Anyone run this setup? How high does the rpm's get on the interstate? By the way I have an auto tranny in it. Thanks for any help.

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With an AW-4 that is going to be a high revving sonofagun. It will probably be around 3000 at 65mph roughly. However as long as you can deal with the rpms, go for it.

sell the 31's and get 33's and regear to 4.56

ive read that some are doing 4.56 with 31's and like it. the 4.0 can handle 3000rpms all day long. i have 4.10, 5spd, and 31's and 3000rpms is not bad. only problems is the driveshaft is spinning faster so you may get driveshaft vibs.

its been covered here many times before. but i will chime in anyway.

right now i have 31s and 4.56s on my 95 xj 4.0 aw4. it does rev high on the freeway but not quite 3000 rpm. i am about 2500 at approx 65 mph. its great having the power i lost with larger tires.

i had to downgrade when i got new tires due to money issues. when i regeared, i knew i would be going bigger tires so i went for the 4.56. sometime in the future i will be going up to 33s when i can aford it.

do the swap to 4.56s and you will be happy. especially when you go to a larger tire

I have 4.56's with 32s, runs about 2700rpm at 70mph. The extra power is alot of fun and mpg is about the same.

SEARCH,but first scroll down about ten threads,then 20,then 30.Theres like 4+ active threads less than a day old on this as we speak!

stewie said:

do the swap to 4.56s and you will be happy. especially when you go to a larger tire

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No you won't be happy. You will miss the fuel mileage & low end torque you had with 31's. JIM.

Do it and don't look back... 4.1's are a waste of $$ (unless you P&P a set already stuffed)

I ran 31's and 4.56's for a year.
your low end tq will be the exact same (gears do not alter the motors power), however, the deeper gearing and increased tq multiplication will make your rig feel like someone removed 1000lbs from it when you were not looking. This in turn actually makes the rig "feel" like it has more power.
all the math in the world will point to 2500rpm at 65mph... the math is not wrong... 4.56's, 31" tire and 2500rpm is about as close to 56mph as you are going to get.
With 31's and 4.56's I got 18.8 - 19.2mpg (running 2500rpm/65mph and at 2750rpm/70mph)... and that is running super swampers... a nice set of all terrains and it would have been noticably better on gas.

A wheeling pal is running 4.10's and 32's... he wishes he had gone 4.56.

I still have 31's and just dropped a boat load of cash on 4.88 and lockers. I have yet to drive it but I knew that I wanted less speed on the top end and more grunt on the lower end.

There are a few other guys that run 31's and 4.88s and love it around town. With your DD and so many miles I think4.56 would be just about perfect for you with the 31-33 tires

Thanks guys. Input helped make up my mind.

i run 31" bfg a/t's, 4.56, aw4, on my dd.
it is slightly high reving, in that, when you punch it, the engine gets up high in the revs.
i love it, its got pep., sounds mean at the high end with a glasspack, mileage aint terrible, not that i care. and you can use your engine as a horn!


dont be scared of mileage, be scared of doing gears twice.