I tried to make it through this whole thread and got to page 7 or 8 and I just couldn't take it anymore! Regardless this is a very informative thread and I'm glad I stumbled on it. I'm thinking of purchasing and XJ soon, and I would have been waaay off if I just bought some gears based on personal experience. I have 2 lifted vehicles and neither of them come quite close to the gear ratios/calculations you guys are running on these jeeps. For instance:
1) 4.88s are too low for the XJ project: My 2001 dodge ram 1500, 5.2L V8 auto, 37x12.50MTR - I ran 3.55s for too long waiting on 4.88s to come out, as 4.56s were the lowest you could fit in the 9.25 rear. 4.56 was "optimal" for my situation according to the "calculators" but I figured they weren't taking into account the significantly larger rolling resistance of the bigger tires. I was glad I held out, and 4.88s worked out perfectly, but when it's wet out, it's really hard to make the rear tires stick... borderline dangerous. Naturally I would assume that, for what I'm looking for in this XJ project, 4.88s would be to low. I guess I underestimated the effect of a 5.2L v8 vs. the 4.0L 6...?
2)4.10s are too tall for the XJ project: My 1994 YJ, 4.0L, manual tranny, 37x12.50 SSR - This setup works just fine on the road, a little more gearing would be nice, but definately not necessary. I was happy with the 12 or so MPGs I was getting, but that's because I was used to the dodge getting around 8 or so. Off road, it was painfully obvious that 4.10s weren't enough. I went pretty much everywhere I wanted to go, but the stress on the drivetrain due to lack of gearing led to way too many broken parts.
Point being, I'm going to run 33s or 35s on my XJ project, and based on previous experience I would have chosen 4.10s with 33s or 4.56 with 35s. I was pretty far off with this "educated guess" if you can call it that. My main concern with this XJ will be fuel mileage and based on what I've read here, I'm thinking 4.88s. I still need to do a little more research before I go buyin' gears, but it seems to me the solution to good gas mileage is finding the gear ratio that will put you in the right RPM range and (again, from what I've read here...) this should be just under 3000 RPM. I live in south louisiana, so hills are rare and this thing will see the majority of it's time on the highway, so off road performance isn't as much of a concern.
Am I on target here?
It may very well be that running 4.56s with no OD has negatively skewed my perception (I often wished I'd got 4.10s). I certainly respect your opinion--it is a decision that would be very costly to change, were one unhappy with the gearing choice one made!
