A 20" Dahon folder was my first gas motorized bike. The Staton friction drive kit w/Subaru 1.35hp 4-stroke was its first transplant. It was a perfect starter MB with excellent manners. Top speed was 27mph. The next step was a 2.2hp Mitsubishi w/Staton rear chain drive. Top speed was 30-something mph. Now the bike had bad manners and became more squirrelly. That, and the fact that it no longer fit in its original carrying case are the reasons I decided to move up to 26" motorized bicycles. Top speed is now 40-something mph, but I like cruising at 32mph.