20"  Designed for children at least 50 to 56 inches tall. Minimum inseam: 23.5 inches (boys frame). 16"  Designed for children at least 41 to 49 inches tall. Minimum inseam: 18 inches (boys frame). 12"  Designed for children at least 36 to 40 inches tall. Minimum inseam: 18 inches (boys frame).