North of Aspen, the Sunnyside Loop is a popular local mountain bike ride that links several local trails. It combines a section of the level Rio Grande Trail and the Smuggler Mountain Road to access the 7 mile Sunnyside Trail system. This 16 mile loop rolls over singletrack, dirt road and bike path with an elevation gain of 3,500 feet.
There is a good trailhead at the start of Smuggler Mountain Road. Start riding up the steep Smuggler Mountain Road to the Iowa Shaft Trail that leads down into the Hunter Valley. Then, climb up Four Corners Road to the Sunnyside Trail. The Sunnyside Trail heads west for 7 miles back down to the Rio Grande Trail bike path that can be followed east back to Aspen.
Overall, Sunnyside Loop is the 115th most popular mountain bike trail of all 175 mountain biking rides in Colorado.