Current road double cranksets are typically 53/39 rings on a 130 or 135BBCD crank. Compacts use a 110 bcd and typically 50/34 rings or sometimes a 36 to get lower gearing wthout going to a triple,and without giving up much on the top end. A triple will give lower gearing if that is what one really needs, due to the use of an even smaller granny ring.