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how much gear for 30" tires?

moparjim1987

NAXJA Forum User
Location
pennsylvania
my 97 cherokee has 166,000 miles on it and it currently has a 2 in. BB and L78-15 trailbreakers. now it seems like when it is loaded down, it really slows down on hills, downshifting into 2nd gear sometimes. do i need 3.73's or 4.10's? u am eventually building a stroker of some sort, so i don't want to have a ton of gear in it, but stock performance would be nice.... thanks for your help.
 
For 31's most people recommend 4.10's, so I would plan ahead of time and get 4.10's. Right now I have 31's & 4.10's (but will be going to 33's soon) and it is nice having more power (ran 31 w/ 3.55's for 2 years).
 
I ran 30's, 4.10's and with an AW4 for a long time. I loved it. I miss it. I'm seriously thinking of dropping back down.


If you're 100% sure you'll go with 31's; My recommendation is to wait to regear until then. Then, after you have the 31's, regear to 4.56's.
 
moparjim1987 said:
my 97 cherokee has 166,000 miles on it and it currently has a 2 in. BB and L78-15 trailbreakers. now it seems like when it is loaded down, it really slows down on hills, downshifting into 2nd gear sometimes. do i need 3.73's or 4.10's? u am eventually building a stroker of some sort, so i don't want to have a ton of gear in it, but stock performance would be nice.... thanks for your help.

dont even touch it, its not worth the $1200 for a reagear job. and 30" tires come on buddy step it up. haah just kiddin, but if your gonna have tires that small dont reagear it its not worth it at alllllll
 
moparjim1987 said:
i heard that the libertys have a dana 30 ifs differential up front. will these gears work in the soild axle dana 30?

Wouldn't it be easier to swap in the whole front axle from a 4cyl XJ with 4.10 gears? You could probably pick up the whole axle for cheaper than the bearings and seals you would need to re-gear yours.
 
moparjim1987 said:
i heard that the libertys have a dana 30 ifs differential up front. will these gears work in the soild axle dana 30?

Nope basically the same as a low pinion XJ with a crush sleeve.. from what Ive been told.. They have issues with them as well..

To the Original Poster of the thread. Don't bother changing your gears till after you get the 31's & lift on there, and even after you get the stroke in and running.. I have been running 4.56's with 33's and with the stroker it has sooooo much grunt I am going back to 4.10's for better mileage.. Since I don't own no trailer queen..14mpg sucks right now...
 
i just lifted 2 inches and 30" bighorns.
i have not noticed any change at all.

but since this is on topic, how do i find my gear ratio?
it is a 92 xj larado 4.0 dana 30 front 8.25 rear.
i got near 20 mpg before the lift. i have not ran a full tank out since the lift.

forgive my dumb question,
thanks
 
chances are it is 3.55 if you have a auto and 3.07 with a stick

Really the difference between stock and a 30 inch tire is minimal and unless you do heavy loads or towing you most likely wont get much gain out of changing ratio. at 31's you start to see a bigger gain by re-gearing to 4:10

a auto trans 4:10 gears and a 30 inch tire is pretty damn nice for towing in my opinon
 
I have been wondering about this myself. 31" tires and 3.55 gears are killing me right now. I am averaging about 12.5 mpg (adjusting for odometer being off due to larger tires). I don't plan to go to bigger tires (at least for another 4+ years) and I do highway driving at 75. I am really looking towards 4.10s because I don't like the sound of 3500rpm while going 75 with 4.56 gears.
 
XJBlackPDX said:
I have been wondering about this myself. 31" tires and 3.55 gears are killing me right now. I am averaging about 12.5 mpg (adjusting for odometer being off due to larger tires). I don't plan to go to bigger tires (at least for another 4+ years) and I do highway driving at 75. I am really looking towards 4.10s because I don't like the sound of 3500rpm while going 75 with 4.56 gears.

So you're currently on 31"s and 3.55s, and your mileage went in the tank? Many people run that combination with little to no real change in power or mileage, but I also noticed a drop in both just going to 30"s with the stock 3.55s. If it's a huge deal, switch back to stock-ish size tires until you're ready to lift, re-gear and throw bigger tires on. That's what I'd do if I knew I wasn't going to address it for 4 years. Sell the 31"s, chalk it up to a lesson learned.
 
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