I have the 245/75/R16's on mine and have not yet regeared. There is a definite loss of power there as the engine and transmission need to work harder in hilly terrain, and MPG's have gone down by about 3-4. I want to regear eventually and am saving up for that. That said, I think I could get along alright without regearing, but it would just be better if I did. Now with 265's I couldn't imagine not regearing, as you wouldn't be able to use overdrive at all! So, in my experience, I would say regearing with 245/75/16's is optional but recommended, where as it would be required with 265/75/16's. Stock gears are 3.73's for 225/75/16's, and Tom recommends 4.10's for 245/75/16 and 4.56's for 265/75/16's. Also keep in mind that to run 245/75/16's you'll need 2 inches of lift, and to run 265/75/16's you'll need 4 inches of lift.
2008 Liberty Sport 4x4 Automatic