The type of offroad tire you choose depends on the type and condition of the terrain you’ll be riding on.  Hard packed terrain requires a softer compound rubber with shorter more closely spaced knobs for optimum traction.  Conversely, sand and loamy soil requires a harder compound with taller knobs more widely spaced to dig into the soil and to self clean.  Popular choices include an intermediate terrain tire which has medium compound rubber with moderately spaced medium height knobs.  These tires are a compromise in traction on very loamy and hard packed terrain, but have improved wear characteristics overall.  Moto MD carries all the top name tires at great prices, with “FREE TIRE MOUNTING” for offroad bikes (wheel off bike).