On what vehicle? A suburban? A geo? Probably not much bigger than 35s or 36s, especially if its a c-clip dana 44 (versus a bearing retainer style 44). Make sure it's not a gov-lock 10 bolt... get it out of there before you go fourwheeling! If memory serves, an '85 K5 wouldn't have dana 44s, but rather 10 bolts. Same axle really, but the gov-lock is miserable - ask me how I know. The front should do just fine on 35s or 36s if you keep it open, and use the throttle within reason. The rear.... if it's open, it should do fine too, just wheel like you got some sense.