knobby

Are there tyres available that have decent offroad grip for the 3.5*17 front and 4.25*17 rear rim? I would like to do some offroading sometimes but do'nt want to buy ANOTHER (already have 2) wheelset... Intermediate/rain tyres are ok for offroad but I want something more knobby :mrgreen:

I run a 19'' tire and am looking to see what everyones opinion is on the best knobby tire for shale, rockys, hard packed trails. I ride nothing but major rocky mountainy trails and keep tearing up tires. i dont ride on any pavement just straight trail. what would you suggest for a tire?