For those of us who live in hilly or mountainous terrain, the number of miles is almost irrelevant. It's the number of feet of climbing that matters. Around here, every 10 miles horizontally results in about 1,000 feet of climbing. My typical ride is around 4,000 feet of climbing so that generally equals about 40 miles. There are a very few somewhat flat routes that we do and the relative effort is so low that I can ride much farther on those routes if I don't get bored.