At Haw Ridge, treat yourself to miles of mountain biking and hiking trails with an added bonus of a paved Greenway that curls around the Clinch River. There are 30-miles of trails at Haw Ridge, ranging from super solid rooted singletracks with tasking climbs and rewarding descents to shoreline trails that are mere feet from the waters of the beautiful Clinch River.
The Knoxville Urban Wilderness Corridor is a really amazing concept created by the Legacy Parks Foundation. Essentially, they've created (and continue to create) a natural connector system that links together some of the most prominent outdoor parks in the Knoxville area. Within its 1,000 acres are tons of trails perfectly designed for mountain biking.
Half an hour from downtown Knoxville is Concord Park, which offers 9-10 miles of solid singletrack trails. The trails are fairly technical with twisty climbing and occasional roots and rocks to watch out for.