Not only is this an outstanding design which performs perfectly, the company REALLY stands behind it.  I've had mine nearly three years and it has gone enough miles that I wore out the tires (actually had a blowout on one).  The one time when I called for a new part, they not only supplied the item (knob) they asked if I needed anything else and when I responded that the bag straps were getting a little frayed, they replaced them also.  All this at NO COST, they even paid the shipping.  SunMountain's service makes them the best buy on the market.