rpm

[shawnxj]

what rpm are y'all turning at 80 and what kind of mileage do you get city/hwy? i put 4.56's in my xj on 37's thinking if i kept my rpms in the 2400 range at 80 that i'd get fairly decent gas mile. well around town i get 12 mpg so now i'm thinking of bumping up to 5.13 which will put my rpms at 2800 at 80 but instead of 2000 rpm at 65 like they are now i'll be closer to 2300

i also didn't think about the rolling mass of 37's when i put the 4.56's in. when i had my original axles i had 4.88's on 35's and i don't remember the mileage being that bad but i never actually checked it

[jeepxj3]

What axles do you have now?

The 4.56 are good for 35s, 4.88 for 37s. is a good start.
You do more off roading and crawling than on road highway, you can go with a bit more gear 4.88 for 35s and 5.13 for 37.

37s are big and heavy.

It's going to be a bit of trial and error for the type of driving that you do. Having said that, the 4.56 and 37s is too high. You need either 4.88 or 5.13s. Tough choice. Which ever you choose, you will want the other.

[shawnxj]

right now i have a hp44 with rcv's and a ford 9". i can spin the 37's with the 4.56's when the tires are cold and i don't have any issues staying in overdrive but i think i'm just oging to do 5.13's and call it done

[jeepman]

I usually play around with this Gear Calculator to find roughly what gears and tires for desired RPM at a given speed...

http://www.grimmjeeper.com/gears.html

[jeepxj3]

5.13s are a very small pinion gear.

[shawnxj]

not on a 9" and for the 44 they're not that bad. i install gears for the jeep club down here all the time and have yet to see a pinion snap. most of the jk's i do get either a 5.13 or 5.38 and granted the ford pinion shaft is slightly smaller then the jk pinion shaft but i don't see either of them breaking. if it does i'll just put dana 50 gears in it. might go ahead and do that anyways