30's and 3.07 workable?

As tire replacement is needed, I am considering moving from 235s to 30 inch tires. The XJ is a 5 speed with 3.07 gearing. A search suggests that 31s are too big for 3.07, but I found nothing relating to 30 inch tires. I typically average between 22 and 25 mpg with 235s where most of my driving is rural -- dirt road, 55 mph secondary roads, and some in-town. For those of you who have moved to 30s, have you sacrificed mileage and 5th gear usability?

I ran 30's with 3.07's for a while. Not the most ideal, but it works, and I could still use 5th gear on the highway (never going uphill though).

Now I'm running 32's and never use 5th gear, just 4th at 2000 rpm's on the highway. 32's and 3.07's suck so much, I can't even see how two of my friends run 33's and 35's with 3.07's... no money to regear I guess (for any of us!)

pec50 said:

As tire replacement is needed, I am considering moving from 235s to 30 inch tires. The XJ is a 5 speed with 3.07 gearing. A search suggests that 31s are too big for 3.07, but I found nothing relating to 30 inch tires. I typically average between 22 and 25 mpg with 235s where most of my driving is rural -- dirt road, 55 mph secondary roads, and some in-town. For those of you who have moved to 30s, have you sacrificed mileage and 5th gear usability?

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If MPG is the major concern you should stick with the 235's until you can regear. I ran 31's with 3.07, lots of stalling, heck I have lots of stalling with my 4.88s and 33's. I never really checked my milleage with the 31's, I had the basic speedo at the time, no odometer.

One thing about the 5 spd's is that you really control your RPM's. You should still be able to use the 5th gear on the flats, but you really need to stay closer to the powerband just above 2k.

I sugest at least looking for some cheap OEM alxe replacements with 3.55 from an auto. There should be plenty of these at local pick-n-pulls, or even better find with a 4 banger, they will most likely have 4.10's.

I wouldn't do it. In fact, I didn't. I re-geared when I went to 235/75x15 tires. The 3.07 gears aren't even deep enough for STOCK size tires, let alone anything larger!

dmillion said:

I wouldn't do it. In fact, I didn't. I re-geared when I went to 235/75x15 tires. The 3.07 gears aren't even deep enough for STOCK size tires, let alone anything larger!

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I have an automatic and think I'm running lower than 3.07. With the 235's, overdrive won't pull even on a gradual slight upgrade unless I start out at 75 or 80. It's to the point now that I leave the lever in "3" instead of "D" for most of my driving.

With the automatic and an I-6 you have 3.55 gears. I never noticed a problem with OD in mine with 235s although it tried to kick out of OD on hills when I ran 30s. Although it was okay with 32s, regearing to 4.56 with those tires made a world of difference. The engine runs in a good powerband and stays in OD when climbing unless I really need to get on it.