What diff gears for 99 XJ with 4L engine, AT, and 30 vs 31 inch tires?
I have D30 front, C8.25 rear diffs.
I live in a semi mountainous area with level (or near level) freeway in valleys and steep freeway in mountains (with 7% grades common, and the occasional 14% grade).
Want to be able to cruise at 70 mph on level freeway and get decent gas mileage doing it. Also want to be able to pull moderate hills (4% or 5% grade) in 4th gear at 70 mph.
Also, need gearing low enough to back up easily on steep hills. i.e. - need low enough reverse. Not worried about 1st because it's lower than reverse. So need diff gears to work for that too.
What diff gears for:
30 x 9.5 R15 tires? Actual tire height manufacturer claims is 29.5". I'm thinking 3.73 diff gears?
31 x 9.5 R16 tires (245/75R16)? Actual tire height manufacturer claims is 30.5". I'm thinking 3.73 or 4.10 diff gears?
Are there gear choices between 3.73 and 4.10 ?
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