The Amasa Back trail is one of the classic rides of Moab. It ascends from Kane Creek on the Colorado River just west of Moab, climbing up onto an outcropping of rock surrounded on three sides by the Colorado.
The Porcupine Rim Trail is the "other" famous classic ride at Moab. At 15.6 miles, requiring expert technical skills, this ride is for advanced bikers who are in good shape. It's one-way with a shuttle car, or a 34-mile loop for the truly insane (10 uphill miles from Moab to the trailhead, 8 flat miles from Jackass Canyon back to the middle of Moab).
This is the world-famous Slickrock Trail near Moab, Utah. This 10.6 mile loop twists and rolls through Navajo sandstone to a breathtaking view over the Colorado River. The Slickrock Trail is rated high technical difficulty and high aerobic requirement. But many MANY "not-very-good" bikers ride this trail, with a few short hikes over the tough spots.
The Poison Spider Mesa trail is one of the "Must Do" rides of Moab. Combining physically demanding biking challenges with great views, this trail is for expert bikers. The trail can be ridden as an out-and-back, but here I describe a 13-mile loop that includes the infamous Portal Trail as the return-route off the mesa. Altitude gain is 1000 feet.