A 1.5" lift accommodates 31" tires. As a compromise for daily driving and occasional offroading, I put on 29.5" on my stock rims, size 245/70R16. All is right with the world. The Grabber AT2's 8" tread width gives my Liberty a nice solid footing on the ground. They're good on pavement, snow, rocks, dirt/sand, and shallow mud. (Get a real mud-terrain tire of you plan to frequent mud bogs!) The tires are annoying in gravel, however, because the grooves are just small enough to collect 1/4" stones, which fly out like bullets once you're on pavement.
Which 1.5" lift are you considering? OME coil springs would give you 1.5" of lift, but since you're going with spacers, I don't know of what else is out there other than Daystar's KJ09123. That's the kit I have, and I'm happy with it. I got a great deal from All J Products (
http://www.boulderbars.com)
If you don't go offroad much, a less-expensive lift leaves you money to buy underbody armor, which is just as important -- if not more -- than offroad tires and ground clearance.
T.J.