What's the difference between a 20" small and a 20" large?
The 20 inch small vs 20 inch large is based on the size of the frame design. As you can see below, the 20 inch small bike has a lower seat height so it fits a smaller child. The rest of the frame geometry is then engineered to fit a child that size.
Seat Height Range (MIn - Max)
20 inch (small) = 20.8 - 26.8 in
20 inch (large) = 22.5 - 28.5 in
Height Range (MIn - Max)
20 inch (small) = 43 - 51 in
20 inch (large) = 45 - 53 in