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Gearing

PSoffe

NAXJA Forum User
Location
So Cal
I have a 2001 with a 4" lift, I am currently running 265/75R16 tires. With the manual trans i get the ever popular 3:07 gear package, it's not bad around town but is a little difficult on the trail.

What would be a good starting point for new gear 3:73, 4:11?

It's an in town daily driver so no freeway but i don't want give too much top end speed either.
 
I'm running 4.11s on 245/75/16. Right now your Xj is set up to do 200mph, lol. You are actually putting a lot of pressure on the engine and transmission with the 3.07s. It takes more pedal and effort to get the tires moving. Matching tires and gears is what you want to do, even if it means giving up doing 95mph at 1500 rpm down the road. With 265s id be looking at least 4.11s maybe pushing 4.56s.
 
The easiest option would be to swap in a 3.55 axle from an automatic XJ and see how you like it. I have 265/75-16 tires and 3.73 gears in my '06 TJ with a manual and it's a sweet spot for it.
 
You can use my gear ratio calculator to see how changes in tire sizes match up with changes in gear ratio. http://www.grimmjeeper.com/gears.html

You should have the AX15 transmission and the NP231 transfer case.

Ratios you can choose from are 3.07, 3.55, 3.73, 4.10, 4.56, and 4.88. More than that in either direction is probably too much.

Keep in mind that advertised tire size is always off a little so the actual numbers won't match 100%. But they should be close.
 
All other things being equal, you can cross-multiply to get yourself into the ball park without giving up too much top-end-

Original tire diameter Original gear ratio
---------------------------------- X -----------------------------
New tire diameter New gear ratio

IIRC, factory tire size was something like 215/75/15 or 225/75/15 on most XJ's. Also, bear in mind this formula only takes into account tire diameter/circumference, not the added weight from running a wider tire.
 
I have a similar size tires (235/85-16) and with the 3.55 gears it really struggles. 4.56 or 4.10/11 would be about perfect for it. 3.73 isn't enough of a jump.
 
I have a similar size tires (235/85-16) and with the 3.55 gears it really struggles. 4.56 or 4.10/11 would be about perfect for it. 3.73 isn't enough of a jump.

A 265/75R16 tire runs between 31" and 32".
I have run 29", 30", 31" and 33" diameter tires over the past 13 years, along with 3.55, 4.11 and 4.56 gears.

For the 265/75R16s, I would run either 4.11 or, even better, 4.56 gears.
Presently I have two sets of wheel and tires, one 31"s and the other 33"s.
It is a blast to drive around town on the 31"s but still has plenty of go to pull the 33"s.
Adjusting the ratio so the engine spins at the same speed as stock, at 60-MPH, may be disappointing since the weight and rolling resistance are greatly increased, along with added wind resistance.

Living and traveling in the West, we have many long, steep grades and having a little lower gear ratio makes driving uphill, and down, more enjoyable.
If you plan on actually wheeling your XJ, 4.56s will be much more fun to drive.
 
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