FATMAP difficulty grade
Radio Flyer is one of the newer trails at Vail, providing "dozens of banked turns and rollers wind from Eagle's Nest down through Vail's lodgepole pine forests." Radio Flyer leads naturally into Lower Radio Flyer.
From the end of Lower Radio Flyer you can easily hop on Big Mamba to keep the flow train rolling! Source: https://www.vail.com/explore-the-resort/activities-and-events/summer-activities/mountain-biking.aspx