With the Mark II you will enjoy features such as fast rolling 20 inch alloy wheels, a universal coupler attaches quickly and easily to most bikes, and the outrigger frame stabilizes and protects the wheels. the Mark II quickly converts to a stroller without using tools which makes it easy for you to switch back and forth between trailer mode and stroller mode whenever you want. The extra-wide aluminum frame design provides more space for each child and the zippered weather shield provides extra protection in poor weather.