Just keep the overall diameter of the tires at or under 32" and you'll be fine. 275/65/18 and 275/55/20 will fit. This all applies to a non lifted WK2.
I'm not sure how much bigger of a tire you could get with the RR 2.5" lift.
'11 Laredo / Bright Silver Metallic / V6 / QT1 / 17" Wheels / Tow
3M 20% tint up front, GY Wrangler Silent Armors, 5000k LED interior and reverse lights
Audio: Pioneer AVH-X1500, Alpine MRX-M55, JL 12W3V3