I don't know about other places in Jax, but you can check this site for other trails in nearby cities.

http://www.dep.state.fl.us/gwt/guide...orth/north.htm

Jax-Balwin is a great trail. So is Gainsville-Hawthorne. They are all worth a visit.

Check out Hanna Park in Jax if you want to go off road--what a great park for bikers! They have miles of trails inside the park, from gavel roads to high-skill level single tracks. You can rent a cabin for $40 a night, rent a boat for the lake, go to the ocean, go mountain biking, and never leave the park. Enjoy.